Showing papers on "Growth medium published in 2013"

Antifungal activity of ZnO nanoparticles and their interactive effect with a biocontrol bacterium on growth antagonism of the plant pathogen Fusarium graminearum

Abstract: Fungal plant pathogens such as Fusarium graminearum cause severe global economic losses in cereals crops, and current control measures are limited. This work addresses the potential for ZnO nanoparticles (NPs) and biocontrol bacteria to be used in plant fungal control strategies. Growth of F. graminearum was significantly (p = 0.05) inhibited by inclusion of the NPs in a mung bean broth agar and in sand. Suspension in mung bean broth medium modified the surface charge, dissolution, and aggregation state of the ZnO NPs, in comparison to processes occurring in water suspension. The ZnO NPs were significantly more inhibitory to fungal growth than micro-sized particles of ZnO, although both types of particles released similar levels of soluble Zn, indicating size-dependent toxicity of the particles. Zn ions produced dose-dependent inhibition, noticeable at the level of soluble Zn released from NPs after seven-day suspension in medium; inhibitory levels caused acidification of the growth medium. Transfer of fungal inoculum after exposure to the ZnO NPs to fresh medium did not indicate adaptation to the stress because growth was still inhibited by the NPs. The ZnO NPs did not prevent metabolites from a biocontrol bacterium, Pseudomonas chlororaphis O6, from inhibiting Fusarium growth: no synergism was observed in the mung bean agar. Because other studies find that soil amendment with ZnO NPs required high doses for inhibition of plant growth, the findings of pathogen growth control reported in this paper open the possibility of using ZnO NP-based formulations to complement existing strategies for improving crop health in field settings.

The metabolic flux phenotype of heterotrophic Arabidopsis cells reveals a complex response to changes in nitrogen supply.

Abstract: The extent to which individual plants utilise nitrate and ammonium, the two principal nitrogen sources in the rhizosphere, is variable and many species require a balance between the two forms for optimal growth. The effects of nitrate and ammonium on gene expression, enzyme activity and metabolite composition have been documented extensively with the aim of understanding the way in which plant cells respond to the different forms of nitrogen, but ultimately the impact of these changes on the organisation and operation of the central metabolic network can only be addressed by analysing the fluxes supported by the network. Accordingly steady-state metabolic flux analysis was used to define the metabolic phenotype of a heterotrophic Arabidopsis thaliana cell culture grown in Murashige and Skoog and ammonium-free media, treatments that influenced growth and biomass composition. Fluxes through the central metabolic network were deduced from the redistribution of label into metabolic intermediates and end products observed when cells were labelled with [1-(13) C]-, [2-(13) C]- or [(13) C6 ]glucose, in tandem with (14) C-measurements of the net accumulation of biomass. Analysis of the flux maps showed that: (i) flux through the oxidative pentose phosphate pathway varied independently of the reductant demand for biosynthesis, (ii) non-plastidic processes made a significant and variable contribution to the provision of reducing power for the plastid, and (iii) the inclusion of ammonium in the growth medium increased cell maintenance costs, in agreement with the futile cycling model of ammonium toxicity. These conclusions highlight the complexity of the metabolic response to a change in nitrogen nutrition.

Tetracycline resistance gene maintenance under varying bacterial growth rate, substrate and oxygen availability, and tetracycline concentration

Abstract: Neither amplification nor attenuation of antibiotic resistance genes (ARG) in the environment are well understood processes. Here, we report on continuous culture and batch experiments to determine how tetracycline (TC), aerobic vs anaerobic conditions, bacterial growth rate, and medium richness affect the maintenance of plasmid-borne TC resistance (Tet(R)) genes. The response of E. coli (a model resistant strain excreted by farm animals) versus Pseudomonas aeruginosa (a model bacterium that could serve as a reservoir for ARGs in the environment) were compared to gain insight into response variability. Complete loss of the Tet(R) RP1 plasmid (56 kb) occurred for P. aeruginosa in the absence of TC, and faster loss was observed in continuous culture at higher growth rates. In contrast, E. coli retained its smaller pSC101 plasmid (9.3 kb) after 500 generations without TC (albeit at lower levels, with ratios of resistance to 16S rDNA genes decreasing by about 2-fold). A higher rate of ARG loss was observed in P. aeruginosa when grown in minimal growth medium (M9) than in richer Luria broth. Faster ARG loss occurred in E. coli under anaerobic (fermentative) conditions than under aerobic conditions. Thus, in these two model strains it was observed that conditions that ease the metabolic burden of plasmid reproduction (e.g., higher substrate and O2 availability) enhanced resistance plasmid maintenance; such conditions (in the presence of residual antibiotics) may be conducive to the establishment and preservation of ARG reservoirs in the environment. These results underscore the need to consider antibiotic concentrations, redox conditions, and substrate availability in efforts to evaluate ARG propagation and natural attenuation.

Influence of resveratrol on oxidative stress resistance and life span in Caenorhabditis elegans.

Abstract: Objectives Resveratrol (3,5,4′-trihydroxy-trans-stilbene), a polyphenol from red wine, has been reported to be beneficial in cases of ageing-related cardiovascular and neurodegenerative diseases owing to its property to reduce oxidative stress. Previous studies on the longevity promoting effect of resveratrol have been partly inconclusive, therefore we set out to investigate whether resveratrol at least promoted longevity in Caenorhabditis elegans under acute oxidative stress conditions. Methods C. elegans was cultured under standard conditions with or without resveratrol. After exposure to juglone-induced acute oxidative stress, the survival rate and hsp-16.2::GFP expression were measured. The influence of resveratrol on life span was recorded also under oxidative stress induced by high glucose concentrations in the growth medium. Key findings No extension of the normal life span of C. elegans was observed either in liquid or solid growth media containing different concentrations of resveratrol. However, resveratrol alleviated juglone-induced lethal oxidative stress, and significantly prolonged the life span of C. elegans under conditions of acute oxidative damage and oxidative stress caused by high concentrations of glucose. Conclusions Resveratrol, as an antioxidant, ameliorated oxidative stress in vivo but did not extend the life span of C. elegans under normal conditions. However, resveratrol did extend life span under conditions of oxidative stress.

Improved growth media and culture techniques for genetic analysis and assessment of biomass utilization by Caldicellulosiruptor bescii

Abstract: Methods for efficient growth and manipulation of relatively uncharacterized bacteria facilitate their study and are essential for genetic manipulation. We report new growth media and culture techniques for Caldicellulosiruptor bescii, the most thermophilic cellulolytic bacterium known. A low osmolarity defined growth medium (LOD) was developed that avoids problems associated with precipitates that form in previously reported media allowing the monitoring of culture density by optical density at 680 nm (OD680) and more efficient DNA transformation by electroporation. This is a defined minimal medium and does not support growth when a carbon source is omitted, making it suitable for selection of nutritional markers as well as the study of biomass utilization by C. bescii. A low osmolarity complex growth medium (LOC) was developed that dramatically improves growth and culture viability during storage, making it a better medium for routine growth and passaging of C. bescii. Both media contain significantly lower solute concentration than previously published media, allowing for flexibility in developing more specialized media types while avoiding the issues of growth inhibition and cell lysis due to osmotic stress. Plating on LOD medium solidified by agar results in ~1,000-fold greater plating efficiency than previously reported and allows the isolation of discrete colonies. These new media represent a significant advance for both genetic manipulation and the study of biomass utilization in C. bescii, and may be applied broadly across the Caldicellulosiruptor genus.

Effect of Growth Media, pH and Temperature on Yeast to Hyphal Transition in Candida albicans

Abstract: The transition of C. albicans from unicellular yeast form to filamentous form i.e., pseudohyphae and hyphae is referred to as morphogenesis. C. albicans has the ability to respond to environmental conditions and accordingly changing its cell morphology. Three main morphological forms of C. albicans are unicellular yeast, pseudohyphae and hyphae. The effect of different growth media (Horse serum medium, RPMI-1640, MSGB), incubation temperatures (34°C, 37°C, 40°C) and pH values (5.4, 6.4, 7.4) on germ tube production by C. albicans was evaluated. Horse serum medium noticeably promotes filamentation while RPMI-1640 medium shows moderate filamentation and MSGB media shows moderately low filamentation. The germ tube of C. albicans developed early in 1.5 hr at high temperature i.e., 40°C. Incubation temperature of 37°C was associated with highest germ tube formation while 34°C shows low filamentation. A pH of 5.4 also induces low filamentation, pH 6.4 gives moderately lower than pH 7.4. A pH of 7.4 was best suited for germ tube induction. The peak of mycelium production appears between 1.5 and 6 hr after inoculation of C. albicans culture. These results suggested that environmental factors are important in selectively favoring yeast or hyphal form, most important being the growth medium, incubation temperature and external pH value.

Isolation and identification of phosphate solubilizer Azospirillum, Bacillus and Enterobacter strains by 16SrRNA sequence analysis and their effect on growth of wheat (Triticum aestivum L.)

Abstract: The aim of the present study was to isolate phosphate solubilizing bacteria from wheat rhizosphere and investigate their potential for plant growth promotion. Three phosphate solubilizing bacterial strains were isolated by serial dilution method from the rhizosphere of wheat grown under wheat-cotton and wheat-rice crop rotation. 16S rRNA gene sequence of the isolates WS-1, T-34 and T-41 showed 98% similarity to those of Azospirillum, Bacillus and Enterobacter sequences in NCBI data base, respectively. The bacterial strain WS-1 clustered with Azospirillum brasilense strains in the phylogenetic tree constructed using NCBI data base sequences of the genus Azospirillum. The bacterial isolate T-34 formed cluster with Bacillus licheniformis strains in the phylogenetic tree constructed using 16S rRNA sequences of the genera Bacillus and Paenibacillus. In the phylogenetic tree constructed using 16S rRNA gene sequences of genus Enterobacter, the isolate T-41 clustered with Enterobacter amnigenus strains. Phosphate solubilizing activity of the bacterial strains in Pikovskaya medium was investigated by molybdate blue color method using spectrophotometer while organic acids produced in the medium were detected on HPLC. In a growth medium containing insoluble tri-calcium phosphate and supplemented with sucrose, maltose, glucose or galactose as single C-source, all the three isolates produced organic acids like acetic acid, citric acid and gluconic acid for phosphate solubilization. Among the organic acids detected, acetic acid was produced in highest amounts by all strains tested in the media containing different sugars. Maximum acetic acid (56.7 mug/ml) was produced by Bacillus strain T-34 in medium supplemented with sucrose and citric acid (36.2 mug/ml) by the same strain on glucose supplemented medium. Oxalic acid was produced by Bacillus strain T-34 (2.89 mug/ml) and Enterobacter strain T-41 (5.93 mug/ml) only in the medium containing galactose as C-source. Maximum amount of gluconic acid (25.4 mug/ml) was produced by Azospirillum strain WS-1 in the medium containing glucose as C-source. Highest P solubilization activity (298.3 mug/ml) was observed in Bacillus strain T-34 grown on sucrose supplemented medium. Maximum P solubilization was detected in Enterobacter strain T-41 (292.2 mug/ml) in medium containing maltose. Azospirillum strain WS-1 showed maximum P solubilization (218.1 mug/ml) in medium containing glucose as single C-source. All the three bacterial strains produced growth hormone IAA in the growth medium supplemented with tryptophan. Quantification on HPLC indicated maximum IAA production (31.15 mug/ml) by Bacillus strain T-34. A pot experiment conducted to study the effect of bacterial isolates on growth of wheat showed that inoculation with Azospirillum, Bacillus and Enterobacter strains increased the grain yield of wheat by 9.3%, 14.8%, 13.1%, respectively over non-inoculated control. Under field conditions, increase in grain yield of plants inoculated with Azospirillum, Bacillus and Enterobacter was 11.2%, 15.7% and 5.6%, respectively compared with non-inoculated plants.These results indicated that bacterial isolates having plant-beneficial traits like phosphate solubilization and IAA production and capable of improving growth of wheat when used as inoculants qualify for production of biofertilizer for wheat crop.

Optimization and partial characterization of culture conditions for the production of alkaline protease from Bacillus licheniformis P003

Abstract: Proteolytic enzymes have occupied a pivotal position for their practical applications. The present study was carried out under shake flask conditions for the production of alkaline protease from Bacillus licheniformis P003 in basal medium containing glucose, peptone, K2HPO4, MgSO4 and Na2CO3 at pH 10. The effect of culture conditions and medium components for maximum production of alkaline protease was investigated using one factor constant at a time method along with its characterization. Maximum level of enzyme production was obtained after 48h of incubation with 2% inoculum size at 42°C, under continuous agitation at 150 rpm, in growth medium of pH 9. Highest enzyme production was obtained using 1% rice flour as carbon source and 0.8% beef extract as organic nitrogen source. Results indicated that single organic nitrogen source alone was more suitable than using in combinations and there was no significant positive effect of adding inorganic nitrogen sources in basal medium. After optimization of the parameters, enzyme production was increased about 20 fold than that of in basal medium. The crude enzyme was highly active at pH 10 and stable from pH 7–11. The enzyme showed highest activity (100%) at 50°C, and retained 78% relative activity at 70°C. Stability studies showed that the enzyme retained 75% of its initial activity after heating at 60°C for 1h. The enzyme retained about 66% and 46% of its initial activity after 28 days of storage at 4°C and room temperature (25°C) respectively. Mn2+ and Mg2+ increased the residual activity of the enzyme, whereas Fe2+ moderately inhibited its residual activity. When pre-incubated with Tween-20, Tween-80, SDS and H2O2, each at 0.5% concentration, the enzyme showed increased residual activity. These characteristics may make the enzyme suitable for several industrial applications, especially in leather industries.

Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica

Abstract: The effects of several physiological parameters on H2 production rate in the unicellular halotolerant cyanobacterium Aphanothece halophytica were investigated. Under nitrogen deprivation, the growth of cells was inhibited, but H2 production rate was enhanced approximately fourfold. Interestingly, cells grown under sulfur deprivation exhibited a decrease in cell growth, H2 production rate, and bidirectional hydrogenase activity. Glucose was the preferred sugar source for H2 production by A. halophytica, but H2 production decreased at high glucose concentrations. H2 production rate was optimum when cells were grown in the presence of 0.75 M NaCl, or 0.4 μM Fe3+, or 1 μM Ni2+. The optimum light intensity and temperature for H2 production were 30 μmol photons m−2 s−1 and 35 °C, respectively. A two-stage culture of A. halophytica was performed in order to overcome the reduction of cell growth in N-free medium. In the first stage, cells were grown in normal medium to accumulate biomass, and in the second stage, H2 production by the obtained biomass was induced by growing cells in N-free medium supplemented with various chemicals for 24 h. A. halophytica grown in N-free medium containing various MgSO4 concentrations had a high H2 production rate between 11.432 and 12.767 μmol H2 mg chlorophyll a (chl a)−1 h−1, a 30-fold increase compared to cells grown in normal medium. The highest rate of 13.804 μmol H2 mg chl a −1 h−1 was obtained when the N-free growth medium contained 0.4 μM Fe3+. These results suggested the possibility of using A. halophytica and some other halotolerant cyanobacteria thriving under extreme environmental conditions in the sea as potential sources for H2 production in the future.

A defined, glucose-limited mineral medium for the cultivation of Listeria spp.

Abstract: Members of the genus Listeria are fastidious bacteria with respect to their nutritional requirements, and several minimal media described in the literature fail to support growth of all Listeria spp. Furthermore, strict limitation by a single nutrient, e.g., the carbon source, has not been demonstrated for any of the published minimal media. This is an important prerequisite for defined studies of growth and physiology, including "omics." Based on a theoretical analysis of previously published mineral media for Listeria, an improved, well-balanced growth medium was designed. It supports the growth, not only of all tested Listeria monocytogenes strains, but of all other Listeria species, with the exception of L. ivanovii. The growth performance of L. monocytogenes strain Scott A was tested in the newly designed medium; glucose served as the only carbon and energy source for growth, whereas neither the supplied amino acids nor the buffering and complexing components (MOPS [morpholinepropanesulfonic acid] and EDTA) supported growth. Omission of amino acids, trace elements, or vitamins, alone or in combination, resulted in considerably reduced biomass yields. Furthermore, we monitored the specific growth rates of various Listeria strains cultivated in the designed mineral medium and compared them to growth in complex medium (brain heart infusion broth [BHI]). The novel mineral medium was optimized for the commonly used strain L. monocytogenes Scott A to achieve optimum cell yields and maximum specific growth rates. This mineral medium is the first published synthetic medium for Listeria that has been shown to be strictly carbon (glucose) limited.

Contribution of hydrogenase 2 to stationary phase H2 production by Escherichia coli during fermentation of glycerol

Abstract: Escherichia coli has four hydrogenases (Hyd), three genes of which are encoded by the hya, hyb, and hyc operons. The proton-reducing and hydrogen-oxidizing activities of Hyd-2 (hyb) were analyzed in whole cells grown to stationary phase and cell extracts, respectively, during glycerol fermentation using novel double mutants. H2 production rate at pH 7.5 was decreased by ~3.5- and ~7-fold in hya and hyc (HDK 103) or hyb and hyc (HDK 203) operon double mutants, respectively, compared with the wild type. At pH 6.5, H2 production decreased by ~2- and ~5-fold in HDK103 and HDK203, respectively, compared with the wild type. At pH 5.5, H2 production was reduced by ~4.5-fold in the mutants compared with the wild type. The total hydrogen-oxidizing activity was shown to depend on the pH of the growth medium in agreement with previous findings and was significantly reduced in the HDK103 or HDK203 mutants. At pH 7.5, Hyd-2 activity was 0.26 U (mg protein)(-1) and Hyd-1 activity was 0.1 U (mg protein)(-1). As the pH of the growth medium decreased to 6.5, Hyd-2 activity was 0.16 U (mg protein)(-1), and Hyd-1 was absent. Surprisingly, at pH 5.5, there was an increase in Hyd-2 activity (0.33 U mg protein)(-1) but not in that of Hyd-1. These findings show a major contribution of Hyd-2 to H2 production during glycerol fermentation that resulted from altered metabolism which surprisingly influenced proton reduction.

Isolation and characterization of high salt tolerant bacteria from agricultural soil

Abstract: Adaptation characteristic of microorganisms in different extreme conditions seeks discoveries in field of pharma, food, & bioenergy sectors. In the present study, new experimental approach was proposed to prove adaptation ability in extreme conditions with growth and development of agricultural soil bacterial species in stepwise adaptation in high salt (NaCl) conditions. Six different bacterial species were isolated from agricultural soil surrounding the Rajkot region. Out of six isolates, two showed salt tolerance up to 10% NaCl concentration. Biochemical and molecular (16S rDNA sequencing) characterization revealed the strains to be Exiguobacterium sp. and Serratia sp. designated as GSD1 and GSD 2 strains. Species were able to adapt upto 10% of NaCl in nutrient broth growth medium. Primary screening for extracellular enzymes (protease, amylase, lipase) secretion unveiled activity of enzymes in nutrient agar plates containing skim milk or starch or mineral oil for protease, amylase and lipase production respectively. This experiment provides the base to link the adaptation capabilities of agricultural soil microorganisms in high salty environment and vice a versa.

EXO modifies sucrose and trehalose responses and connects the extracellular carbon status to growth.

Abstract: Plants have the capacity to adapt growth to changing environmental conditions. This implies the modulation of metabolism according to the availability of carbon (C). Particular interest in the response to the C availability is based on the increasing atmospheric levels of CO2. Several regulatory pathways that link the C status to growth have emerged. The extracellular EXO protein is essential for cell expansion and promotes shoot and root growth. Homologous proteins were identified in evolutionarily distant green plants. We show here that the EXO protein connects growth with C responses. The exo mutant displayed altered responses to exogenous sucrose supplemented to the growth medium. Impaired growth of the mutant in synthetic medium was associated with the accumulation of starch and anthocyanins, altered expression of sugar-responsive genes, and increased abscisic acid levels. Thus, EXO modulates several responses related to the C availability. Growth retardation on medium supplemented with 2-deoxy-glucose, mannose, and palatinose was similar to the wild type. Trehalose feeding stimulated root growth and shoot biomass production of exo plants whereas it inhibited growth of the wild type. The phenotypic features of the exo mutant suggest that apoplastic processes coordinate growth and C responses.

Characterization of residual medium peptides from Yersinia pestis cultures.

Abstract: Here we demonstrate that when Yersinia pesitis is grown in laboratory media, peptides from the medium remain associated with cellular biomass even after washing and inactivation of the bacteria by different methods. These peptides are characteristic of the type of growth medium and of the manufacturer of the medium, reflecting the specific composition of the medium. We analyzed biomass-associated peptides from cultures of two attenuated strains of Yersinia pestis [KIM D27 (pgm-) and KIM D1 (lcr-)] grown in several formulations of 4 different media (tryptic soy broth (TSB), brain–heart infusion (BHI), Luria–Bertani broth (LB), and glucose (G) medium) made from components purchased from different suppliers. Despite the range of growth medium sources and the associated manufacturing processes used in their production, a high degree of peptide similarity was observed for a given medium recipe; however, notable differences in the termination points of select peptides were observed in media formulated using pro...

Effect of bacteria containing acc deaminase on growth of wheat seedlings grown with chromium contaminated water

Abstract: Chromium (Cr) is considered as toxic environmental pollutant and causes harmful effects on growth and development of plants and human health. Usually, high level of ethylene (a plant hormone) is produced in plants in response to any biotic or abiotic stress. Negative effect of Cr-imposed stress on plants may be minimized by using bacteria possessing an enzyme 1-amino-cyclopropane-1- carboxylic acid (ACC)-deaminase. The aim of this study was to investigate the effect of plant growth-promoting bacteria containing ACC-deaminase on wheat under different levels of Cr applied to growth medium. Experiments were conducted under laboratory and lath house conditions. Results of this study demonstrated that inoculation of wheat seeds with two strains of bacteria Pseudomonas fluorescens (Q14) and Bacillus thuringiensis (KAP5) significantly increased the root length (up to 208%), shoot length (up to 67%), root dry weight (up to 140%) and shoot dry weight (up to 71%) respectively as compared to uninoculated control plants. Strain KAP5 possessing both ACC-deaminase as well as phosphate solubilizing activity was found to be the most effective in improving the plant growth compared to uninoculated control in both sand and soil experiments. Inoculation also significantly increased the accumulation of Cr in root and shoots compared to uninoculated control, where the Cr uptake 80.8µg/g dry mass and 69.9µg/g dry mass in root and shoot respectively, was observed. These findings indicated that ACC-deaminase producing bacterial strains could play vital role in improving the plant growth under metal-stress condition and they may enhance bioremediation process in Cr-contaminated environment. Moreover, presence of dual plant growth promoting trait such as ACC-deaminase and phosphate solubilizing activity could have more promising effect on plant growth and Cr removal than the single trait bacterium.

An in vitro study of Lactobacillus plantarum strains for the presence of plantaricin genes and their potential control of the table olive microbiota

Abstract: Sixteen Lactobacillus plantarum strains, isolated from fermented table olives, were studied for the presence and expression of genes involved in the production of bacteriocins, pheromones and other peptides. The presence of 13 genes that belong to pln locus was monitored, while for the study of gene expression, producer strains were cultured in growth medium with variant salinity (0, 4, 6, and 8 % NaCl) and pH (3.5, 4.0, 4.5, and 6.4). The effect of producer strain on the growth of indicator microorganisms was evaluated using a well diffusion assay. In parallel, Real-Time PCR was employed to monitor the genetic expression of plnE/F and plnJ/K genes for strains that revealed the highest antimicrobial activity. The well diffusion assay showed that the growth of Lactobacillus pentosus was inhibited by six L. plantarum strains when cultured on control medium (0 % NaCl, pH 6.4). Moreover, when the same growth medium was supplemented with 4 and 6 % NaCl, the growth of L. pentosus was inhibited by three and two L. plantarum strains, respectively. Growth of L. pentosus was favoured when L. plantarum strains were cultured on a growth medium with lowered pH (3.5, 4.0, and 4.5). No inhibition of pathogens was observed, but in a few cases, inhibition of Aureobasidium pullulans was detected. The Real-Time PCR assay revealed that the expression of genes was dependent on producer strains and growth phase, whereas inhibition of indicator strains was enhanced in earlier stages of the growth curve in the presence of NaCl, although similar counts were obtained.

Quorum sensing influences growth and photosynthetic membrane production in high-cell-density cultivations of Rhodospirillum rubrum.

Abstract: The facultative anoxygenic photosynthetic bacterium Rhodospirillum rubrum exhibits versatile metabolic activity allowing the adaptation to rapidly changing growth conditions in its natural habitat, the microaerobic and anoxic zones of stagnant waters. The microaerobic growth mode is of special interest as it allows the high-level expression of photosynthetic membranes when grown on succinate and fructose in the dark, which could significantly simplify the industrial production of compounds associated with PM formation. However, recently we showed that PM synthesis is no longer inducible when R. rubrum cultures are grown to high cell densities under aerobic conditions. In addition a reduction of the growth rate and the continued accumulation of precursor molecules for bacteriochlorophyll synthesis were observed under high cell densities conditions. In the present work, we demonstrate that the cell density-dependent effects are reversible if the culture supernatant is replaced by fresh medium. We identified six N-acylhomoserine lactones and show that four of them are produced in varying amounts according to the growth phase and the applied growth conditions. Further, we demonstrate that N-acylhomoserine lactones and tetrapyrrole compounds released into the growth medium affect the growth rate and PM expression in high cell density cultures. In summary, we provide evidence that R. rubrum possesses a Lux-type quorum sensing system which influences the biosynthesis of PM and the growth rate and is thus likely to be involved in the phenotypes of high cell density cultures and the rapid adaptation to changing environmental conditions.

Growth Medium Optimization for Biomass Production of a Probiotic Bacterium, Lactobacillus rhamnosus ATCC 7469

Abstract: This study was undertaken to determine the glucose, yeast extract, tryptone and Tween 80 concentrations in a cultivation medium for optimal biomass production of a probiotic bacterium, Lactobacillus rhamnosus ATCC 7469 Using response surface methodology, a central composite rotatable design was applied to allocate treatment combinations A polynomial regression model containing linear, quadratic, cubic and quartic terms was used for analysis of the experimental data Effects involving all four factors evaluated were found to be significant and the strongest effect was given by tryptone concentration Estimated optimum conditions of the factors for the growth of L rhamnosus were as follows: glucose = 44% (w/v), yeast extract = 60% (w/v), tryptone = 60% (w/v) and Tween 80 = 11 mL/L The optimum-point medium gave higher counts of viable cells, specific growth rate and biomass productivity than de Man, Rogosa and Sharpe and the center-point media Practical Applications With increasing demand for food products containing probiotic microorganisms from health-conscious consumers, there arises a need to establish effective fermentation techniques for probiotic biomass production Medium formulation, fermentation parameters and fermentor design play important roles to ensure optimal results This study highlights a statistical approach to optimizing medium formulation for a probiotic lactic acid bacteria strain, which is known for its high nutritional demands The optimal medium formulation obtained from this study can be used for improving Lactobacillus rhamnosus fermentation as it is capable of producing more viable cells than de Man, Rogosa and Sharpe medium, which is generally recognized and used as a suitable medium for lactic acid bacteria cultivation

Escherichia coli Growth Changes by the Mediated Effects After Low-Intensity Electromagnetic Irradiation of Extremely High Frequencies

Abstract: Water is the major constituent of environmental medium and biological systems. The effects occurring in water as a result of low-intensity electromagnetic irradiation (EMI) in extremely high frequencies are supposed to be the primary mechanism to create conditions for biological responses. The EMI effects on Escherichia coli, after irradiation of their suspension, are most probably water-mediated. Indirect effects of EMI at 51.8, 53, 70.6, and 73 GHz frequencies on bacteria, through water, assay buffer (Tris-phosphate buffer with inorganic salts at low or moderate concentrations), or peptone growth medium were studied. The mediated effects of 70.6 and 73 GHz irradiated water, assay buffer, and growth medium on E. coli growth characteristics were insignificant. But the results were different for 51.8 and 53 GHz. EMI mediated effects on bacterial growth were clearly demonstrated. The effects were more strongly expressed with 53 GHz. Moreover, it was shown that 70.6 and 73 GHz similarly suppressed the cell growth after direct irradiation of E. coli in water or on solid medium. Interestingly, for 51.8 and 53 GHz the bacterial growth decreases after suspension irradiation was less, compared to the direct irradiation of bacteria on solid medium. Especially, it was also more expressed in case of 53 GHz. Also with electron microscopy, EMI-induced bacterial cell sizes and structure different changes were detected. In addition, the distinguished changes in surface tension, oxidation-reduction potential and pH of water, assay buffer, growth medium, and bacterial suspension were determined. They depended on EMI frequency used. The differences could be associated with the partial absorbance of EMI energy by the surrounding medium, which depends on a specific frequency. The results are crucial to understand biophysical mechanisms of EMI effects on bacteria.

Enhanced production of cell-bound cholesterol oxidase from Rhodococcus sp. NCIM 2891 by the statistical method

Abstract: Classical (one-variable-at-a-time) and statistical methods (Plackett-Burman and Central composite design) were used to optimise growth medium for the production of cholesterol oxidase (COX) from Rhodococcus sp. NCIM 2891. COX activities from the classically and statistically optimised media were 0.75 and 3.25 U/ml, respectively. The statistically optimised medium had 4.33- and 9.7-fold higher enzymatic activity than the classically optimised and un-optimised basal medium, respectively. The ratio of enzyme production to cell growth rate was 29-fold higher in our statistically optimised medium than in the basal medium, indicating that the enzyme production could be classified as mixed type of growth. Cell-bound COX accounted for 90.68 ± 2 % of the total enzymatic activity of the growth medium. Interactions between the COX-inducing substrate cholesterol and medium growth substrates yeast extract and (NH4)2HPO4 significantly enhanced the production of cell-bound COX. Our results validate the statistical approach as a potential technique for achieving the large-scale production of cell-bound COX from Rhodococcus sp. NCIM 2891.

A low-cost Lactobacillus salivarius L29 growth medium containing molasses and corn steep liquor allows the attainment of high levels of cell mass and lactic acid production

Abstract: The aim of the present work was to formulate a Lactobacillus salivarius L29 industrial fermentation medium High cell numbers and good levels of lactic acid by a L salivarius L29 were obtained after shake flask fermentation using molasses as the sole carbon source and corn steep liquor (CSL (industrial grade); an organic source of N) as the principal nitrogen source The optimum concentrations of molasses and CSL facilitating good cell growth and high-level lactic acid production were found to be 6 and 6% (both v/v), respectively The maximum cell yield was 202 × 10 9 CFU/mL, thus about 15% lower than that obtained when MRS broth was employed for 5-L fermenters culture Lactic acid production upon growth in industrial broth was 105 g/L; the total sugar content of the medium was 118 g/L (sucrose: glucose: fructose 68:14:18; w/w/w) Upon growth in De Man, Rogosa and Sharpe (MRS) broth (the total sugar content of which was 127 g/L, all of which was glucose), the lactic acid yield was 120 g/L The optimized industrial growth medium was significantly more economical than were conventional broths Keywords : Lactobacillus salivarius L29, molasses, corn steep liquor, culture medium optimization, lactic acid African Journal of Biotechnology Vol 12(16), pp 2013-2018

Effect of environmental conditions on the growth of Cryptosporiopsis spp. causing leaf and nut blight on cashew (Anacardium occidentale Linn.)

Abstract: A new disease (cashew leaf and nut blight) in Tanzania caused by a fungus related to the genus Cryptosporiopsis was identified in 2006 The present work investigated the effects of environmental factors on the growth of Cryptosporiopsis spp causing blight on cashew The mycelial growth, colony character and sporulation pattern of 10 fungal isolates, grown on seven different culture media namely, corn meal agar (CMA), malt extract agar (MEA), tryptone dextrose agar (TDA), potato carrot agar (PCA), water agar (WA), potato dextrose agar (PDA) and host leaf agar were observed after 10 days of incubation at 25±2°C The colony diameter, culture characteristics and sporulation of the 10 isolates were greatly influenced by the type of growth medium used The best mycelial extension was recorded in 12 h alternating light/dark followed by total light and total dark conditions, respectively Seven media were evaluated for best growth of the fungi that is, Cryptosporiopsis spp grew maximum on WA followed by host leaf extract media and PDA, respectively but least grew on the TDA medium The growth ofCryptosporiopsis spp was maximum in temperature range of 25 to 30°C The most suitable pH level for growth of fungus was 70 and 60 These results will be useful for fungal taxonomic studies Key words: Cryptosporiopsis spp, culture media, light, temperature

Physiological, biochemical and molecular responses of the halophilic cyanobacterium Aphanothece halophytica to Pi-deficiency

Abstract: We studied the responses of a halophilic cyanobacterium Aphanothece halophytica at surplus (normal composition of growth medium containing 125 µM PO43−), sufficient (the minimum concentration supporting optimal growth, 22 µM PO43−) and deficient (no external supply of Pi) concentrations of inorganic phosphate (Pi). The cyanobacterium was able to grow well in Pi-deficient conditions until the end of incubation (14 days), though at a marginally reduced rate. The cellular P-quota in Pi-surplus cells at the end of incubation was 2.7 times that of their initial P-quota (0.75 µmol mg protein−1), and remained fairly high (0.442 µmol mg protein−1) even in Pi-deficient medium. However, cultures growing in Pi-sufficient medium (22 µM PO43−), upon transfer to Pi-deficient medium, exhibited a rapid decline in cellular P level. Furthermore, cells growing in Pi-surplus medium showed a rapid efflux of P into the external medium. Aphanothece halophytica exhibited a biphasic phosphate transport system involving both high-...

Glucose-induced activation of H+-ATPase in Dunaliella salina and its role in hygromycin resistance

Abstract: Dunaliella salina, a eukaryotic microalga, is known for its highly halophilic nature. The high level of salts in growth medium for this alga has made its genetic transformation a comparatively difficult procedure, particularly during the selection stage. The high salt content decreases the efficiency of most antibiotics which are being used as selection markers. Studies pertaining to the interrelationship between salt concentration and antibiotic sensitivity are scarce in Dunaliella. During our previous experiment at genetic transformation of Dunaliella, an inverse relationship between the amount of antibiotic hygromycin and sodium chloride in the medium was revealed. A possible link between plasma membrane activity and the hygromycin sensitivity was investigated in the present study by modulating plasma membrane H+-ATPase activity using glucose. Glucose-induced activation of H+-ATPase, reduced the tolerance of D. salina to the antibiotic hygromycin. Hygromycin concentration required for selection during genetic transformation of Dunaliella was lowered from 100 to 25 mg L−1 in the presence of 10 mM glucose. Conversely, the inhibitors of the plasma membrane H+-ATPase, orthovanadate and diethylstilbestrol were found to inhibit the glucose activation at concentrations of 10 and 15 μM, respectively. The activation of H+-ATPase by glucose was further confirmed through H+-ATPase assay and medium acidification experiments. The results indicated that the sensitivity of Dunaliella to antibiotic is related to H+-ATPase and the possible involvement of pH gradient, created through H+-ATPase activation during drug transport.

Molecular identification and biodegradation of 3-chloropropionic acid (3CP) by filamentous fungi-Mucor and Trichoderma species isolated from UTM agricultural land

Abstract: Aims: This study was carried out to further characterize fungal species that could degrade 3-chloropropionic acid (3CP)as sole source of carbon and energy. Methodology and Results: Both fungi were able to grow on 3CP after 10 days on solid minimal media. Based on sequencing of its segment of 18S rRNA these isolates were identified as Mucor sp. SP1 and Trichoderma sp. SP2. The isolated strains were not able to grow on media plates containing 10 mM of 2,2-dichloropropionate (2,2DCP) as sole source of carbon. 3CP degradation was observed in liquid minimal medium containing 10 mM 3CP after 18 days culture period. The chloride ion released was detected in both growth medium containing Mucor sp. SP1 and Trichoderma sp. SP2. At least 80% of 10 mM 3CP was utilized in the growth medium. Conclusion, significance and impact of study: Dehalogenase enzyme that can degrade α-chloro-substituted haloalkanoic acids for example 2,2DCP is well studied up to protein crystallization. Very few reports on the degradation of β-chloro-substituted haloalkanoic acids such as 3CP and none from fungi. This study is considered important because it can be compared to that of well-documented α-chloro-substituted haloalkanoic acids degradation. This is the first study to indicate fungal growth on 3CP as sole carbon and energy sources.