Showing papers in "Fems Microbiology Reviews in 1993"
TL;DR: The biochemical and genetic characteristics of these antimicrobial proteins are reviewed and common elements are discussed between the different classes of bacteriocins produced by these Gram-positive bacteria.
Abstract: Lactic acid bacteria produce a variety of bacteriocins that have recently come under detailed investigation. The biochemical and genetic characteristics of these antimicrobial proteins are reviewed and common elements are discussed between the different classes of bacteriocins produced by these Gram-positive bacteria.
2,013 citations
TL;DR: The following review will discuss the successful application of several of the metabolic products produced by lactic acid bacteria in food systems.
Abstract: Lactic acid bacteria produce a variety of metabolic products that are capable of interfering with the growth of other microbes. These bacterial end products have been applied to food systems to prevent the growth of certain undesirable bacteria. The following review will discuss the successful application of several of the metabolic products produced by lactic acid bacteria in food systems.
490 citations
TL;DR: While direct evidence that high affinity mechanisms for iron acquisition function as bacterial virulence determinants has been provided in only a small number of cases, it is likely that many if not all such systems play a central role in the pathogenesis of infection.
Abstract: Most of the iron in a mammalian body is complexed with various proteins. Moreover, in response to infection, iron availability is reduced in both extracellular and intracellular compartments. Bacteria need iron for growth and successful bacterial pathogens have therefore evolved to compete successfully for iron in the highly iron-stressed environment of the host's tissues and body fluids. Several strategies have been identified among pathogenic bacteria, including reduction of ferric to ferrous iron, occupation of intracellular niches, utilisation of host iron compounds, and production of siderophores. While direct evidence that high affinity mechanisms for iron acquisition function as bacterial virulence determinants has been provided in only a small number of cases, it is likely that many if not all such systems play a central role in the pathogenesis of infection.
419 citations
TL;DR: Chitinase induction in plants is not considered solely as an antifungal resistance mechanism, but there is some circumstantial evidence to suggest a morphogenetic role despite the apparent absence of the substrate in plant cells.
Abstract: There has been a considerable amount of recent research aimed at elucidating the roles of chitinase in fungi and plants. In filamentous fungi and yeasts, chitinase is involved integrally in cell wall morphogenesis. Chitinase is also involved in the early events of host-parasite interactions of biotrophic and necrotrophic mycoparasites, entomopathogenic fungi and vesicular arbuscular mycorrhizal fungi. In plants, induction of chitinase and other hydrolytic enzymes is one of a coordinated, often complex and multifaceted defense mechanism triggered in response to phytopathogen attack. Chitinase induction in plants is not considered solely as an antifungal resistance mechanism. Plant chitinases can be induced by various abiotic factors as well and there is some circumstantial evidence to suggest a morphogenetic role despite the apparent absence of the substrate in plant cells. Finally, some chitinases and other chitin-binding proteins including some plant lectins share chitin-binding domains as part of their molecular structure and provide fuel for the so-called ‘lectin-chitinase’ debate and speculation for the origin of chitinase in plants.
390 citations
TL;DR: In this review the metabolic pathways involved in product formation from citrate are described, the bioenergetic consequences of this metabolism for the lactic acid bacteria are discussed and detailed information on some key enzymes in the citrate metabolism is presented.
Abstract: Citrate metabolism plays an important role in many food fermentations involving lactic acid bacteria. Since citrate is a highly oxidized substrate, no reducing equivalents are produced during its degradation, resulting in the formation of metabolic end products other than lactic acid. Some of these end products, such as diacetyl and acetaldehyde, have very distinct aroma properties and contribute significantly to the quality of the fermented foods. In this review the metabolic pathways involved in product formation from citrate are described, the bioenergetic consequences of this metabolism for the lactic acid bacteria are discussed and detailed information on some key enzymes in the citrate metabolism is presented. The combined knowledge is used for devising strategies to avoid, control or improve product formation from citrate.
377 citations
TL;DR: "All stood amazed, until an old woman, tottering out from among the crowd, put her hand to her brow, and peering under it in his face for a moment exclaimed, 'Sure enough! it is Rip Van Winkle-it is himself!'
Abstract: \"All stood amazed, until an old woman, tottering out from among the crowd, put her hand to her brow, and peering under it in his face for a moment exclaimed , 'Sure enough! it is Rip Van Winkle-it is himself. Welcome home again, old neighbour-Why, where have you been these twenty long years?\"' lrving, W. An analogical \"field\" construct in cellular biophysics: history and present status. \"These germs-these bacilli-are transparent bodies. Like glass. Like water. To make them visible you must stain them. Well, my dear Paddy, do what you will, some of them won't stain; they won't take cochineal, they won't take any methylene blue, they won't take gentian violet, they won't take any colouring matter. Consequently, though we know as scientific men that they exist, we cannot see them.\" Sir Ralph Bloomfield-Bonington. The Doctor's Dilemma.
321 citations
297 citations
TL;DR: It is concluded that pursuit of research on beneficial effects of lactic acid bacteria could be promising for ecological therapy of mucosal diseases, and for development of original and flexible vectors for targeting in the gastrointestinal tract.
Abstract: There is in 1993 no proven medical indication of lactic acid bacteria (LAB) for therapy or immunomodulation in man. However, within the bulk of publications, rigorous trials have now opened rational fields of research on beneficial effects of LAB. These include lactose digestion, cholesterol metabolism, diarrheal disorders, prophylaxis of intestinal or urogenital infections, immunomodulation or even oral vaccination. We try here to analyse these studies, considering LAB as pharmacological agents, and conclude that pursuit of research could be promising for ecological therapy of mucosal diseases, and for development of original and flexible vectors for targeting in the gastrointestinal tract.
296 citations
TL;DR: This review will examine current knowledge and outstanding problems regarding the proteolytic system in lactococci and also the extent to which the lactococcal system provides a model for understanding proteolysis in other groups of lactic acid bacteria.
Abstract: The inability of lactic acid bacteria to synthesize many of the amino acids required for protein synthesis necessitates the active functioning of a proteolytic system in those environments where protein constitutes the main nitrogen source. Biochemical and genetic analysis of the pathway by which exogenous proteins supply essential amino acids for growth has been one of the most actively investigated aspects of the metabolism of lactic acid bacteria especially in those species which are of importance in the dairy industry, such as the lactococci. Much information has now been accumulated on individual components of the proteolytic pathway in lactococci, namely, the cell envelope proteinase(s), a range of peptidases and the amino acid and peptide transport systems of the cell membrane. Possible models of the proteolytic system in lactococci can be proposed but there are still many unresolved questions concerning the operation of the pathway in vivo. This review will examine current knowledge and outstanding problems regarding the proteolytic system in lactococci and also the extent to which the lactococcal system provides a model for understanding proteolysis in other groups of lactic acid bacteria.
289 citations
TL;DR: Special selection criteria for LAB for use in the fermentation of sausages and vegetables as well as for the malolactic fermentation in wine are discussed.
Abstract: Lactic acid bacteria (LAB) are the most important bacteria used in food fermentations. Apart from general demands for starter cultures from the view of safety, technological effectiveness and economics, numerous specific aspects have to be considered when selecting strains for the different food fermentations. Therefore selection criteria for LAB depend on the type and the desired characteristics of the final product, the desired metabolic activities, the characteristics of the raw materials and the applied technology. Special selection criteria for LAB for use in the fermentation of sausages and vegetables as well as for the malolactic fermentation in wine are discussed.
272 citations
TL;DR: This work not only includes the biochemistry of the enzymes and the bioenergetics of the processes, but also the genetics of the genes encoding the energy transducing proteins.
Abstract: In the discovery of some general principles of energy transduction, lactic acid bacteria have played an important role. In this review, the energy transducing processes of lactic acid bacteria are discussed with the emphasis on the major developments of the past 5 years. This work not only includes the biochemistry of the enzymes and the bioenergetics of the processes, but also the genetics of the genes encoding the energy transducing proteins. The progress in the area of carbohydrate transport and metabolism is presented first. Sugar translocation involving ATP-driven transport, ion-linked cotransport, heterologous exchange and group translocation are discussed. The coupling of precursor uptake to product product excretion and the linkage of antiport mechanisms to the deiminase pathways of lactic acid bacteria is dealt with in the second section. The third topic relates to metabolic energy conservation by chemiosmotic processes. There is increasing evidence that precursor/product exchange in combination with precursor decarboxylation allows bacteria to generate additional metabolic energy. In the final section transport of nutrients and ions as well as mechanisms to excrete undesirable (toxic) compounds from the cells are discussed.
TL;DR: Analysis of heat shock protein function in Saccharomyces cerevisiae by molecular genetic techniques has revealed only a minority of the heat shock proteins of this organism having appreciable influences on thermotolerance, suggesting physiological perturbations and the accumulation of trehalose with heat stress may be more important in the development of thermot tolerance during a preconditioning heat shock.
Abstract: The heat shock response is an inducible protective system of all living cells. It simultaneously induces both heat shock proteins and an increased capacity for the cell to wisthstand potentially lethal temperatures (an increased thermotolerance). This has lead to the suspicion that these two phenomena must be inexorably linked. However, analysis of heat shock protein function in Saccharomyces cerevisiae by molecular genetic techniques has revealed only a minority of the heat shock proteins of this organism having appreciable influences on thermotolerance. Instead, physiological perturbations and the accumulation of trehalose with heat stress may be more important in the development of thermotolerance during a preconditioning heat shock. Vegetative S. cerevisiae also acquires thermotolerance through osmotic dehydration, through treatment with certain chemical agents and when, due to nutrient limitation, it arrests growth in the GI phase of the cell cycle. There is evidence for the activities of the cAMP-dependent protein kinase and plasma membrane ATPase being very important in thermotolerance determination. Also, intracellular water activity and trehalose probably exert a strong influence over thermotolerance through their effects on stabilisation of membranes and intracellular assemblies. Future investigations should address the unresolved issue of whether the different routes to thermotolerance induction cause a common change to the physical state of the intracellular environment, a change that may result in an increased stabilisation of cellular structures through more stable hydrogen bonding and hydrophobic interactions.
TL;DR: Analyses of motif compositions indicate that all hydrogenases, except those of class VI, must contain some common motifs probably participating in the formation of hydrogen activation domains and electron transfer domains, and that the 30 hydrogenases have evolved from at least three different ancestors.
Abstract: Thirty sequenced microbial hydrogenases are classified into six classes according to sequence homologies, metal content and physiological function. The first class contains nine H2-uptake membrane-bound NiFe-hydrogenases from eight aerobic, facultative anaerobic and anaerobic bacteria. The second comprises four periplasmic and two membrane-bound H2 -uptake NiFe(Se)-hydrogenases from sulphate-reducing bacteria. The third consists of four periplasmic Fe-hydrogenases from strict anaerobic bacteria. The fourth contains eight methyl-viologen- (MV), factor F420- (F420) or NAD-reducing soluble hydrogenases from methanobacteria and Alcaligenes eutrophus H16. The fifth is the H2-producing labile hydrogenase isoenzyme 3 of Escherichia coli. The sixth class contains two soluble tritium-exchange hydrogenases of cyanobacteria. The results of sequence comparison reveal that the 30 hydrogenases have evolved from at least three different ancestors. While those of class I, II, IV and V hydrogenases are homologous, i.e. sharing the same evolutionary origin, both class III and VI hydrogenases are neither related to each other nor to the other classes. Sequence comparison scores, hierarchical cluster structures and phylogenetic trees show that class II falls into two distinct clusters composed of NiFe- and NiFeSe-hydrogenases, respectively. These results also reveal that class IV comprises three distinct clusters: MV-reducing, F420-reducing and NAD-reducing hydrogenases. Specific signatures of the six classes of hydrogenases as well as some subclusters have been detected. Analyses of motif compositions indicate that all hydrogenases, except those of class VI, must contain some common motifs probably participating in the formation of hydrogen activation domains and electron transfer domains. The regions of hydrogen activation domains are highly conserved and can be divided into two categories. One corresponds to the ‘nickel active center’ of NiFe(Se)-hydrogenases. It consists of two possible specific nickel-binding motifs, RxCGxCxxxH and DPCxxCxxH, located at the N- and C-termini of so-called large subunits in the dimeric hydrogenases, respectively. The other is the H-cluster of the Fe-hydrogenases. It might comprise three motifs on the C-terminal half of the large subunits. However, the motifs corresponding to the putative electron transfer domains, as well as their polypeptides chains, are poorly or even not at all conserved. They are present essentially on the small subunits in NiFe-hydrogenases. Some of these motifs resemble the typical ferredoxin-like Fe-S cluster binding site. The variation of the sequences in these regions might determine the specific interaction between the external electron transfer domains of hydrogenases and their electron carriers. For example, the C-terminal cysteine-histidine rich region of the small subunits are distinguishable between those of H2-uptake, H2-producing, MV-reducing, F420-reducing and NAD-reducing NiFe(Se)-hydrogenases.
TL;DR: Several systems controlling gene expression have been identified and transcription attenuation seems frequent, and among the attenuation mechanisms identified, one resembles that controlling amino acid biosynthesis in many bacteria by ribosome stalling at codons corresponding to limiting amino acid.
Abstract: The recent description of large clusters of biosynthetic genes in the chromosome of Lactococcus lactis and, to a lesser extent, of Lactobacillus, has brought some information on gene organization and control of gene expression in these organisms. The genes involved in a given amino acid biosynthetic pathway are clustered at a single chromosomal location and form an operon. Additional genes which are not required for the biosynthesis are present within some operons. Genetic signals are, in general, similar to those found in other prokaryotes. Several systems controlling gene expression have been identified and transcription attenuation seems frequent. Among the attenuation mechanisms identified, one resembles that controlling amino acid biosynthesis in many bacteria by ribosome stalling at codons corresponding to limiting amino acid. The others are different and might be related to a new class of attenuation mechanism. Preliminary evidence for a new type of regulatory mechanism, involving a metabolic shunt, is also reviewed.
TL;DR: The major microbial methylating agents are methylcobalamin (CH 3 CoB 12 ), involved in the methylation of mercury, lead and tin and the metalloids arsenic, selenium, tellurium and germanium as mentioned in this paper.
Abstract: Microbial formation and transformation of organometallic and organometalloid compounds comprise significant components of biogeochemical cycles for the metals mercury, lead and tin and the metalloids arsenic, selenium, tellurium and germanium. Methylated derivatives of such elements can arise as a result of chemical and biological mechanisms and this frequently results in altered volatility, solubility, toxicity and mobility. The major microbial methylating agents are methylcobalamin (CH 3 CoB 12 ), involved in the methylation of mercury, tin and lead, and S -adenosylmethionine (SAM), involved in the methylation of arsenic and selenium. Evidence for the methylation of other toxic metal(loid)s is sparse. Biomethylation may result in metal(loid) detoxification since methylated derivatives may be excreted readily from cells, are often volatile and may be less toxic, e.g. organoarsenicals. However, for mercury, low yields of methylated derivatives and the existence of more efficient resistance mechanisms, e.g. reduction of Hg 2+ to Hg 0 , suggest a lower significance in detoxification. Bioalkylation has only been characterised in detail for arsenic. Microorganisms can accumulate organometal(loid)s, a phenomenon relevant to toxicant transfer to higher organisms. As well as bioaccumulation, many microorganisms are capable of the degradation and detoxification of organometal(loid) compounds by, e.g. demethylation and dealkylation. Several organometal(loid) transformations have potential for environmental bioremediation.
TL;DR: It is argued that there are several additional transporters for glucose that have not yet been identified that act by a facilitated diffusion mechanism and are unknown at present.
Abstract: The yeast Saccharomyces cerevisiae consumes mono- and disaccharides preferentially to any other carbon source. Since sugars do not freely permeate biological membranes, cellular uptake of these compounds requires the action of ‘transporters’. The purpose of this review is to summarize the present knowledge on sugar transport in this organism. Yeast cells show two transporters for monosaccharides, the so-called glucose and galactose transporters that act by a facilitated diffusion mechanism. In the case of glucose transport, which also acts upon d-fructose and d-mannose, two components with high- and low-affinity constants have been identified kinetically. Activity of the high-affinity component is dependent on the presence of active kinases whereas activity of the low-affinity component is independent of the presence of these enzymes. Three genes, SNF3, HXT1 and HXT2, encode three different glucose transporters with a high affinity for the substrates and are repressed by high concentrations of glucose in the medium. Kinetic studies suggest that at least one additional gene exists that encodes a transporter with a low affinity and is expressed constituently. The present view is that there are several additional transporters for glucose that have not yet been identified. Galactose transport has only one natural substrate, d-galactose, and is encoded by the gene GAL2. Expression of this gene is induced by galactose and repressed by glucose. Two transporters for disaccharides have been identified in S. cerevisiae: maltose and α-methylglucoside transporters. These transporters are H+-symports that depend on the electrochemical proton gradient and are independent of the ATP level. The gene that encodes the maltose transporter is clustered with the other two genes required for maltose utilization in a locus that is found repeated at different chromosomal locations. Its expression is induced by maltose and repressed by glucose. The rate of sugar uptake in yeast cells is controlled by changes in affinity of the corresponding transporters as well as by an irreversible inactivation that affects their Vmax. The mechanisms involved in these regulatory processes are unknown at present.
TL;DR: This review outlines the recent progress in the molecular analysis of bacteriophage, bacteriophile resistance and counter resistance, and the construction of novel resistance mechanisms based on the phage genome itself.
Abstract: The study of bacteriophage-host interactions has been instrumental in the development of genetic systems in many genera, and laid many of the foundations of modern molecular genetics. Research into bacteriophage and bacteriophage resistance in the lactic acid bacteria has moved into a new and exciting dimension in recent years. Mechanisms such as adsorption inhibition, restriction and modification, and abortive infection which have been detected and described phenotypically over the past decade are now being subjected to molecular analysis, and this has led to a better understanding of the nature and variety of resistance systems employed by lactic acid bacteria to combat phage attack. In addition, analysis of different bacteriophage has increased our knowledge of these ubiquitous particles to the point where it is possible to construct novel phage resistances based on the phage genome itself. This review outlines the recent progress in the molecular analysis of bacteriophage, bacteriophage resistance and counter resistance, and the construction of novel resistance mechanisms.
TL;DR: This review focuses on the functions of nodulation (nod) genes in the interaction between rhizobia and legumes, the key bacterial determinants of the signal exchange between the two symbiotic partners.
Abstract: This review focuses on the functions of nodulation (nod) genes in the interaction between rhizobia and legumes. The nod genes are the key bacterial determinants of the signal exchange between the two symbiotic partners. The product of the nodD gene is a transcriptional activator protein that functions as receptor for a flavonoid plant compound. This signaling induces the expression of a set of nod genes that produces several related Nod factors, substituted lipooligosaccharides. The Nod factors are then excreted and serve as signals sent from the bacterium to the plant. The plant responds with the development of a root nodule. The plant-derived flavonoid, as well as the rhizobial signal, must have distinct chemical structures which guarantee that only matching partners are brought together.
TL;DR: Comparative spectroscopic analyses revealed that phylogenetically distinct organisms expressed copious quantities of spectrally distinct redox-active biomolecules during autotrophic growth on soluble iron.
Abstract: Bacteria capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Comparative spectroscopic analyses revealed that phylogenetically distinct organisms expressed copious quantities of spectrally distinct redox-active biomolecules during autotrophic growth on soluble iron. Thiobacillus ferroxidans, Leptospirillum ferrooxidans, Sulfobacillus thermosulfidooxidans, and Metallosphaera sedula possessed iron respiratory chains dominated by a blue copper protein, a novel red cytochrome, a novel yellow protein, and a novel yellow cytochrome, respectively. Further investigation of each type of respiratory chain will be necessary to deduce the advantages and disadvantages of each.
TL;DR: Bacterial dissimilatory reduction of iron and sulphur in extremely acidic environments is described and evidence for reduction at two disused mine sites is presented, within stratified 'acid streamers' growths and in sediments from an acid mine drainage stream.
Abstract: Bacterial dissimilatory reduction of iron and sulphur in extremely acidic environments is described. Evidence for reduction at two disused mine sites is presented, within stratified 'acid streamers' growths and in sediments from an acid mine drainage stream. A high proportion (approx. 40%) of mesophilic heterotrophic acidophiles were found to be capable of reducing ferric iron (soluble and insoluble forms) under microaerophilic and anoxic conditions. Mixed cultures of Thiobacillus ferrooxidans and Acidiphilium-like isolate SJH displayed cycling of iron in shake flask and fermenter cultures. Oxido-reduction of iron in mixed cultures was determined by oxygen concentration and availability of organic substrates. Some moderately thermophilic iron-oxidis- ing bacteria were also shown to be capable of reducing ferric iron under conditions of limiting oxygen when grown in glycerol/yeast extract or elemental sulphur media. Cycling of iron was observed in pure cultures of these acidophiles. Sulphate-reducing bacteria isolated from acid streamers could be grown in acidified glycerol/yeast extract media (as low as pH 2.9), but not in media used conventionally for their laboratory culture. An endospore-forming, non-motile rod resembling Desulfotomaculum has been isolated. This bacterium has a wide pH spectrum, and appears to be acid-tolerant rather than acidophilic.
TL;DR: This review gives an overview about the mechanisms used by pathogenic bacteria to accomplish the difficult task of regulation of their virulence potential in response to environmental changes.
Abstract: Pathogens have developed many strategies for survival in animals and humans which possess very effective defense mechanisms. Although there are many different ways, in which pathogenic bacteria solved the problem to overcome the host defense, some common features of virulence mechanisms can be detected even in phylogenetically very distant bacteria (Finlay and Falkow (1989) Microb. Rev. 6 1375–1383). One important feature is that the regulation of expression of virulence factors and the exact timing of their expression is very important for many of the pathogenic bacteria, as most of them have to encounter different growth situations during an infection cycle, which require a fast adaptation to the new situation by the expression of different factors. This review gives an overview about the mechanisms used by pathogenic bacteria to accomplish the difficult task of regulation of their virulence potential in response to environmental changes. In addition, the relationship of these virulence regulatory systems with other signal transduction mechanisms not involved in pathogenicity is discussed.
TL;DR: This review describes the different strategies where lactic acid bacteria or their enzymes were used to reduce the ripening time of cheese.
Abstract: The ripening of cheese is a slow and consequently an expensive process. The economic advantage of rapid development of more intense cheese flavour in shorter periods of time would be substantial. Lactic acid bacteria play a key role during ripening and can therefore be used as accelerating agents. This review describes the different strategies where lactic acid bacteria or their enzymes were used to reduce the ripening time of cheese. The advantages, limitations and technical feasibility as well as the commercial potential of the different approaches are also considered.
TL;DR: In this article, the mechanism of bio-leaching or in situ leaching is discussed in terms of close physical and chemical association between the fungal hyphae and mineral phases in the ore.
Abstract: Leaching of silicate ores, particularly nickel laterites, with the aid of heterotrophic organisms has been briefly reviewed. Samples of laterite ores from Greece were characterised mineralogically and a number of microorganisms isolated from them. One of these organisms (code FI) was successfully acclimatized to 6400 ppm nickel. Samples of the high-grade Greek Kastoria nickel laterite were leached with sulphuric acid and a number of organic acids. Sulphuric and citric acids extracted over 60 and 40% of the contained nickel, respectively, but the other acids employed were less efficient leachants. Oxalic acid precipitated nickel oxalate. Roughly the same extraction of iron was observed. The main leaching parameter was confirmed to be hydrogen ion concentration, although complexation with organic anions was a contributor. Organism FI (a strain of Penicillium) was used in comparison with organisms from various culture collections to bioleach nickel from samples of the low-grade Greek Litharakia nickel laterite. The organisms were cultivated in a mixture of a sugar-based nutrient mineral medium and finely ground ore. Several penicillia and aspergilli leached 55–60% of the contained nickel and cobalt, and 25–35% of the iron when sucrose was the carbon source, but FI was not efficient. However, in molasses medium, Fl extracted nearly 40% of the nickel. Biosorption and bioprecipitation reactions were observed. The mechanism of bioleaching or in situ leaching is discussed in terms of close physical and chemical association between the fungal hyphae and mineral phases in the ore. This accounted for the low overall hydrogen ion concentration observed during bioleaching.
TL;DR: The microorganisms used for the mercury retention experiments were natural isolate and genetically engineered bacteria that contained the merA gene and batch experiments were carried out under different conditions to obtain kinetic data of the reductase activity for whole cells and the crude extract.
Abstract: The microorganisms used for the mercury retention experiments were natural isolates and genetically engineered bacteria. All mercury-resistant strains contained the merA gene. Column experiments with these strains were carried out by immobilizing them on different support materials. To obtain kinetic data of the reductase activity for whole cells and the crude extract, batch experiments were carried out under different conditions.
TL;DR: Several hypotheses for the possible mode of action of choline in affecting fungal morphology are discussedHere, choline influences mycelial morphology, apparently by controlling branch initiation over a wide range of concentrations.
Abstract: Choline is an essential metabolite for the growth of filamentous fungi. It occurs most notably as a component of the major membrane phospholipid, phosphatidyl choline (lecithin), and fulfills a major role in sulphate metabolism in the form of choline-o-sulphate in many species. Choline is usually synthesised endogenously, but exogenous choline can also be taken up, either to compensate for metabolic deficiencies in choline-requiring mutants such as those of Aspergillus nidulans and Neurospora crassa, or as a normal function by species such as Fusarium graminearum which do not require added choline for growth. F. graminearum has a highly specific constitutive uptake system for this purpose. Recent studies have begun to indicate that choline also plays an important role in hyphal and mycelial morphology. Over a wide range of concentrations, choline influences mycelial morphology, apparently influences mycelial morphology, apparently by controlling branch initiation. At high concentrations of added choline, branching is inhibited but specific growth rate is unaffected, leading to the production of rapidly extending, sparsely branched mycelia. Reduction of choline concentration allows a progressive increase in branching. Additionally, in choline-requiring mutants which have a very reduced content of choline, multiple tip-formation and apical branching occurs. Just prior to cessation of growth in choline-starved cultures of A. nidulans choline-requiring mutants, hyphal morphology changes due to a brief phase of unpolarised growth to produce spherical swellings called ballons, at or near hyphal apices. The precise mechanism by which choline affects fungal morphology is not yet known, although in A. nidulans it appears to be at least partially due to the influence of membrane composition on the synthesis of the hyphal wall polymer chitin. Several hypotheses for the possible mode of action of choline in affecting fungal morphology are discussed here.
TL;DR: In this article, an enrichment culture of hot spring water samples with pyrite as substrate has provided acidophiles with novel growth characteristics: with these bacteria, the range of conditions under which rapid microbial oxidation of mineral sulphides has been demonstrated has been extended.
Abstract: Enrichment culture of hot spring water samples with pyrite as substrate has provided acidophiles with novel growth characteristics: with these bacteria, the range of conditions under which rapid microbial oxidation of mineral sulphides has been demonstrated has been extended. The upper temperature limit for bacterial mineral oxidation in reactors has been raised. The dissolution of pyrite occurred during growth of Sulfolobus-like thermophiles up to almost 90C. The most efficient extraction of copper from chalcopyrite occurred at 80–85C. With moderate thermophiles, rapid oxidation of minerals was obtained during autotrophic growth in the absence of supplemental CO2: a mixed enrichment culture was active in pyrite dissolution at 45–50C in reactors gassed only with air which contrasted with poor growth by well-studied moderate thermophiles in the absence of enhanced CO2 concentrations.
TL;DR: Data will be presented that characterize two restriction-/modification systems, the codon usage and the promoter sequences of Paracoccus, and details will be given about the extrachromosomal localization of a duplicated cytochrome oxidase subunit I gene on one of the ParacOCcus megaplasmids.
Abstract: In bioenergetic research Paracoccus denitrificans has been used as an interesting model to elucidate the mechanisms of bacterial energy transduction. Genes for protein complexes of the respiratory chain and for proteins which are involved in periplasmic electron transport have been cloned and sequenced. Conjugational gene transfer has allowed the construction of site-specific mutant strains. Complementation experiments did not only open the field for site-directed mutagenesis and investigation of the structure/function relationship of the various electron-transport proteins, but also allowed first insights into processes like oxygen-dependent gene regulation or the assembly of electron-transport complexes. Also data will be presented that characterize two restriction-/modification systems, the codon usage and the promoter sequences of Paracoccus. Details will be given about the extrachromosomal localization of a duplicated cytochrome oxidase subunit I gene on one of the Paracoccus megaplasmids.
TL;DR: An overview of carbon and nitrogen metabolism in the photosynthetic bacteria is given, with particular emphasis on work carried out with mutants, and areas in which the biochemical genetics approach could be applied successfully are indicated.
Abstract: The biochemical genetics approach is defined as the use of mutants, in comparative studies with the wild-type, to obtain information about biochemical and physiological processes in complex metabolic systems. This approach has been used extensively, for example in studies on the bioenergetics of the photosynthetic bacteria, but has been applied less frequently to studies of intermediary carbon and nitrogen metabolism in phototrophic organisms. Several important processes in photosynthetic bacteria — the regulation of nitrogenase synthesis and activity, the control of intracellular redox balance during photoheterotrophic growth, and chemotaxis — have been shown to involve metabolism. However, current understanding of carbon and nitrogen metabolism in these organisms is insufficient to allow a complete understanding of these phenomena. The purpose of the present review is to give an overview of carbon and nitrogen metabolism in the photosynthetic bacteria, with particular emphasis on work carried out with mutants, and to indicate areas in which the biochemical genetics approach could be applied successfully. In particular, it will be argued that, in the case of Rhodobacter capsulatus and Rb. sphaeroides, two species which are fast-growing, possess a versatile metabolism, and have been extensively studied genetically, it should be possible to obtain a complete, integrated description of carbon and nitrogen metabolism, and to undertake a qualitative and quantitative analysis of the flow of carbon and reducing equivalents during photoheterotrophic growth. This would require a systematic biochemical genetic study employing techniques such as HPLC, NMR, and mass spectrometry, which are briefly discussed. The review is concerned mainly with Rb. capsulatus and Rb. sphaeroides, since most studies with mutants have been carried out with these organisms. However, where possible, a comparison is made with other species of purple non-sulphur bacteria and with purple and green sulphur bacteria, and recent literature relevant to these organisms has been cited.
TL;DR: The structure of glutamine synthetase (GS) enzymes from diverse bacterial groups fall into three distinct classes, and different regulatory mechanisms, to ensure optimal utilization of nitrogen substrates, control the GS enzyme in each class.
Abstract: The structure of glutamine synthetase (GS) enzymes from diverse bacterial groups fall into three distinct classes. GSI is the typical bacterial GS, GSII is similar to the eukaryotic GS and is found together with GSI in plant symbionts and Streptomyces, while GSIII has been found in two unrelated anaerobic rumen bacteria. In most cases, the structural gene for GS enzyme is regulated in response to nitrogen. However, different regulatory mechanisms, to ensure optimal utilization of nitrogen substrates, control the GS enzyme in each class.