Showing papers in "International Microbiology in 2001"

Screening of antimicrobial activities in red, green and brown macroalgae from Gran Canaria (Canary Islands, Spain).

Abstract: Extracts from 44 species of seaweed from Gran Canaria (Canary Islands, Spain) were screened for the production of antibacterial and antifungal compounds against a panel of Gram-negative and Gram-positive bacteria, mycobacteria, yeasts and fungi. A total of 28 species displayed antibacterial activity, of which six also showed antifungal activity. Asparagopsis taxiformis and Cymopolia barbata were the species with the strongest activities against the broadest spectrum of target microorganisms. All the species with antibacterial activity were active against Gram-positive bacteria, whereas only two species, A. taxiformis and Osmundea hybrida, were active against mycobacteria. The production of secondary metabolites with antimicrobial activities by the macroalgae was also studied under different conditions, although no common trend for bioactivity was observed.

Classification and mode of action of membrane-active bacteriocins produced by gram-positive bacteria.

Abstract: Bacteriocins are ribosomally synthesized antimicrobial peptides produced by microorganisms belonging to different eubacterial taxonomic branches. Most of them are small cationic membrane-active compounds that form pores in the target cells, disrupting membrane potentials and causing cell death. The production of small cationic peptides with antibacterial activity is a defense strategy found not only in bacteria, but also in plants and animals. Bacteriocins are classified according to different criteria by different authors; in this review, we will summarize the principal bacteriocin classifications, highlight their main physical and chemical characteristics, and describe the mechanism of some selected bacteriocins that act at the membrane level.

The branching order and phylogenetic placement of species from completed bacterial genomes, based on conserved indels found in various proteins

Abstract: The presence of shared conserved inserts and deletions (indels or signature sequences) in proteins provides a powerful means for understanding the evolutionary relationships among the Bacteria. Using such indels, all of the main groups within the Bacteria can be defined in clear molecular terms and it has become possible to deduce that they branched from a common ancestor in the following order: Low G + C gram-positive --> High G+C gram-positive --> Deinococcus Thermus --> Cyanobacteria --> Spirochetes --> Aquifex-Chlamydia-Cytophaga --> Proteobacteria-1 (epsilon, delta) --> Proteobacteria-2 (alpha) --> Proteobacteria-3 (beta) --> Proteobacteria -4 (gamma). The usefulness of this approach for understanding bacterial phylogeny was examined here using sequence data from various completed bacterial genomes. By using 12 indels in highly conserved and widely represented proteins, the species from all 41 completed bacterial genomes were assigned to different groups; and the observed distribution of these indels in different species was then compared with that predicted by the signature sequence model. The presence or absence of these indels in various proteins in different bacteria followed the pattern exactly as predicted: and, in more than 450 observations, no exceptions or contradictions in the placement of indels were observed. These results provide strong evidence that lateral gene transfer events have not affected the genes containing these indels to any significant extent. The phylogenetic placement of bacteria into different groups based on signature sequences also showed an excellent correlation with the 16 S rRNA with 39 of the 41 species assigned to the same group by both methods. These results strongly vindicate the usefulness of the signature sequence approach to understanding phylogeny within the Bacteria and show that it provides a reliable and internally consistent means for the placement of bacterial species into different groups and for determining the relative branching order of the groups.

Ciliate cryptobiosis: a microbial strategy against environmental starvation

Abstract: This review outlines the main features of ciliate resting-cyst formation or encystment. It represents a strategy against several environmental stresses (such as starvation), which involves a highly gene-regulated cell differentiation process and originates a more resistant, differentiated form or resting cyst. This process is mainly characterized by drastic cytoplasmic dehydration that induces a general metabolic rate decrease, intense autophagic activity, the formation of a permeable cyst wall protecting the cell against the adverse environmental conditions, and a gene-silencing mechanism after opening the specific encystment genes.

Potential of Burkholderia cepacia RQ1 in the biodegradation of heavy crude oil

Abstract: The potential of Burkholderia cepacia strain RQ1 in the biodegradation of heavy crude oil (Maya) was assessed to develop an active indigenous bacterial consortium for the bioremediation of crude oil-polluted systems in Nigeria. The heavy crude oil (Maya) was utilized as sole source of carbon, attaining maximum cell densities of 10(8) cfu ml(-1) from an initial 10(5) cfu ml(-1) in 15 days. Biomass also increased with oil concentrations up to 0.8% (w/v). Growth rates ranged from 0.028 h(-1) to 0.036 h(-1) and degradation rates decreased with increasing concentrations of oil from 0.009 day(-1) to 0.004 day(-1). The quantity of oil metabolized increased significantly (P < 0.05) with increasing concentrations of oil. However, the growth of the bacterium was inhibited at crude oil concentrations beyond 6% (w/v). The pH of the culture media also dropped significantly (P < 0.05) during the 15-day test period, while the non-asphaltic fractions of the oil were significantly reduced (by about 89%) during the same period. The bacterium harbours a plasmid of about 10 kb that lacks restriction sites for the endonucleases Asp718, BamHI and PstI.

ABC transporters in the protozoan parasite Leishmania.

Abstract: ATP-binding cassette (ABC) transporters constitute one of the biggest and most conserved protein families in the evolutionary scale. Many of them are of enormous clinical relevance, due to their relationship with genetic diseases and drug resistance during the treatment of cancer and infectious diseases. Leishmaniasis is a major and globally widespread group of parasitic diseases, whose treatment has been complicated by the expansion of resistance to conventional drugs. Here, we review the current knowledge about ABC transporters in Leishmania spp, with special attention to their relationship with the drug-resistance phenotype.

Changes in the photosynthetic apparatus of diatoms in response to low and high light intensities.

Abstract: The centric diatom Cyclotella cryptica and two strains of the pennate diatom Phaeodactylum tricornutum were grown under low and high light intensities (300 lux and 3,000 lux) over 4–6 weeks. Growth was monitored by repetitive cell count. The culture media were replaced weekly to avoid morphological and biochemical alterations caused by nutrient depletion. The ultrastructure of the cells was examined by transmission electron microscopy. Alterations in the light-harvesting antenna systems were investigated by Western immunoblotting. Both diatoms reduced the plastid area, i.e. decreased the amount of thylakoid lamellae, under high light intensity. The thylakoids still ran in groups of three with parallel orientation within the chloroplasts. The girdle band lamellae were not affected. The amounts of storage compounds and vacuoles increased. SDS-PAGE of total cell protein followed by Western immunoblotting with antisera directed against subunits of the light-harvesting antenna systems of C. cryptica (cc-antiserum) and the cryptophyte Cryptomonas maculata (cmac-antiserum) revealed that both diatoms reduced the amount of antenna polypeptides under increased light intensity. The cc-antiserum immunodecorated two bands with relative molecular masses (M r) of 18,000 and 22,000 in C. cryptica. Both decreased under high light conditions to 67.2±6.1%. Five to seven bands in the M r range of 14,000–27,000 were recognized in P. tricornutum. They decreased to 83±5.3%. Furthermore, the immunolabeling pattern for both strains differed under the two light regimes. The cmac-antiserum immunodecorated two polypeptides with M r of 24,000 and 23,000 in C. cryptica, while both strains of P. tricornutum had five polypeptides in the M r range of 14,000–24,000 that showed some differences in staining intensities between the two strains and in response to the light intensity applied.

Speciation of termite gut protists: the role of bacterial symbionts

Abstract: At least 12 termite gut protists have been named because of their bacterial symbionts. Dozens more species are diagnosed by epi- and endosymbionts and more still have regular bacterial associations referred to in their species description. Molecular systematic studies have begun to identify these bacteria, but the ecological relations with their protist bionts are still unknown. Recent findings of acetogenic spirochetes in termite guts may explain the peculiar arrangement of spirochetes on some of these protists. Other bacteria function as motility or chemotactic symbionts of these protists. The size and shape of the parabasal body, a Golgi complex, are morphological characters of the Parabasalia (trichomonads, hypermastigids) that may be influenced by regular, heritable epi- and endosymbiotic bacteria.

Cyanobacterial diversity in extreme environments in Baja California, Mexico: a polyphasic study

Abstract: Cyanobacterial diversity from two geographical areas of Baja California Sur, Mexico, were studied: Bahia Concepcion, and Ensenada de Aripez. The sites included hypersaline ecosystems, sea bottom, hydrothermal springs, and a shrimp farm. In this report we describe four new morphotypes, two are marine epilithic from Bahia Concepcion, Dermocarpa sp. and Hyella sp. The third, Geitlerinema sp., occurs in thermal springs and in shrimp ponds, and the fourth, Tychonema sp., is from a shrimp pond. The partial sequences of the 16S rRNA genes and the phylogenetic relationship of four cyanobacterial strains (Synechococcus cf. elongatus, Leptolyngbya cf. thermalis, Leptolyngbya sp., and Geitlerinema sp.) are also presented. Polyphasic studies that include the combination of light microscopy, cultures and the comparative analysis of 16S rRNA gene sequences provide the most powerful approach currently available to establish the diversity of these oxygenic photosynthetic microorganisms in culture and in nature.

Arundifungin, a novel antifungal compound produced by fungi: biological activity and taxonomy of the producing organisms.

Abstract: Echinocandins, the lipopeptide class of glucan synthase inhibitors, are an alternative to ergosterol-synthesis inhibitors to treat candidiasis and aspergillosis. Their oral absorption, however, is low and they can only be used parenterally. During a natural product screening program for novel types of glucan synthesis inhibitors with improved bioavailability, a fungal extract was found that inhibited the growth of both a wild-type Saccharomyces cerevisiae strain and the null mutant of the FKS1 gene (fks1::HIS). The mutant strain was more sensitive to growth inhibition, suggesting that the fungal extract could contain an inhibitor of glucan synthesis. A novel acidic steroid, named arundifungin, was purified from a fungal extract obtained from a liquid culture of Arthrinium arundinis collected in Costa Rica. Arundifungin caused the same pattern of hallmark morphological alterations in Aspergillus fumigatus hyphae as echinocandins, further supporting the idea that arundifungin belongs to a new class of glucan synthesis inhibitors. Moreover, its antifungal spectrum was comparable to those of echinocandins and papulacandins, preferentially inhibiting the growth of Candida and Aspergillus strains, with very poor activity against Cryptococcus. Arundifungin was also detected in nine other fungal isolates which were ecologically and taxonomically unrelated, as assessed by sequencing of the ITS1 region. Further, it was also found in two more Arthrinium spp from tropical and temperate regions, in five psychrotolerant conspecific isolates collected on Macquarie Island (South Pacific) and belonging to the Leotiales, and in two endophytes collected in central Spain (a sterile fungus belonging to the Leotiales and an undetermined coelomycete).

Enzymatic systems of inorganic pyrophosphate bioenergetics in photosynthetic and heterotrophic protists: remnants or metabolic cornerstones?

Abstract: An increasing body of biochemical and genetic evidence suggests that inorganic pyrophosphate (PPi) plays an important role in protist bioenergetics. In these organisms, two types of inorganic pyrophosphatases [EC 3.6.1.1, namely soluble PPases (sPPases) and proton-translocating PPases (H+-PPases)] that hydrolyse the PPi generated by cell anabolism, thereby replenishing the orthophosphate pool needed for phosphorylation reactions, are present in different cellular compartments. Photosynthetic and heterotrophic protists possess sPPases located in cellular organelles (plastids and mitochondria), where many anabolic and biosynthetic reactions take place, in addition to H+-PPases, which are integral membrane proteins of the vacuolysosomal membranes and use the chemical energy of PPi to generate an electrochemical proton gradient useful in cell bioenergetics. This last category of proton pumps was considered to be restricted to higher plants and some primitive photosynthetic bacteria, but it has been found recently in many protists (microalgae and protozoa) and bacteria, thus indicating that H+-PPases are much more widespread than previously thought. No cytosolic sPPase (in bacteria, fungi and animal cells) has been shown to occur in these lower eukaryotes. The widespread occurrence of these key enzymes of PPi metabolism among evolutionarily divergent protists strongly supports the ancestral character of the bioenergetics based on this simple energy-rich compound, which may play an important role in survival under different biotic and abiotic stress conditions.

Recent findings in the modern RNA world

Abstract: It is assumed that modern life forms arose from a molecular ancestor in which RNA molecules both stored genetic information and catalyzed biochemical reactions. In modern cells, these functions are carried out, respectively, by DNA and proteins, but diverse cellular RNAs are also involved in key cellular functions. In this paper, we review the cellular RNAs that are ubiquitous and/or that perform essential biological functions, and we discuss the evolutionary relationships of such RNAs with a prebiotic RNA world. This unexpected biological diversity of cellular RNAs and the crucial functions they perform in cellular metabolism demonstrate the complexity of an RNA-driven metabolism in an ancient RNA world and in modern life. Cellular RNAs are involved in translation (tRNA and rRNA) but also in ribosome maturation (snoRNA) and more generally in RNA processing (snRNA and snoRNA), replication (telomerase RNA), editing, protein translocation (SRP RNA), cellular transport (vRNA) and translation quality control (tmRNA). In addition, the function of many other cellular RNAs has not yet been determined. Future investigations of RNA function will allow us to better understand not only early evolutionary biological processes but also the central metabolism of modern cells.

Intracellular bacteria in ciliates.

Abstract: Ciliates are frequently colonized by other micro-organisms. The large size of ciliate cells offers habitats for hundreds to thousands of bacteria in different compartments, such as cytoplasm, nuclei and even perinuclear spaces. Size, phagocytic feeding habit and other features appear to be favorable pre-adaptations of ciliates for symbiosis with bacteria. Certain intracellular bacteria are permanent symbionts that are not infectious, whereas others are highly infectious. Both types show specific adaptations. With their wide spectrum of phylogenetic positions, intracellular bacteria in ciliates show relationships to different taxa of free-living bacteria and even archaea. Certain symbionts may be deleterious for their host ciliates, whereas others may provide a selective advantage under appropriate conditions or even be essential for the host cells. Depending on the nature of a symbiont, its prevalence in a host population may be low or high. Symbionts that express a killer toxin affecting non-infected ciliates achieve high infection rates in a host population, whereas certain infectious bacteria may only show a low prevalence.

Global market: shellfish imports as a source of reemerging food-borne hepatitis A virus infections in Spain

Abstract: A total of 16 mollusk imports from South America to Spain, including clam and scallop species, were analyzed for hepatitis A virus (HAV), due to the great concern about this type of food after an important hepatitis A outbreak in eastern Spain in September 1999. In addition, clams from the stock that had caused the outbreak were also tested. Of the 17 stocks, four were positive for the presence of HAV RNA as demonstrated by RT-PCR and Southern hybridization. Contradictory analyses confirmed the results of the primary tests in all cases. The findings obtained in this work strongly support the role of mollusk imports from endemic areas of HAV as an important vehicle of hepatitis A, and demonstrate the imperative need for sanitary control measures to prevent future outbreaks of this disease.

Lectin activity of Lentinus edodes.

Abstract: The hemagglutinating activity of submerged mycelium and culture liquid for four strains of Lentinus edodes (Berk.) Sing [L. edodes (Berk.) Pegler] was studied in the search for lectins. The hemagglutinating activity of culture liquid was substantially higher, compared with mycelium. The carbohydrate-binding capacity of the agglutinins was established, and the lectin activity of extracts from mycelia grown on several agar media was elucidated in relation to fruiting. The lectin activity of L. edodes was examined at different morphogenetic steps: mycelium, brown mycelial film, primordium, and fruiting body. Hemagglutination titers at the brown film step were higher than in the mycelium, whereas activity at the primordial and fruiting bodies steps decreased. Lectins seem to be involved in the formation of hyphal aggregates of brown mycelial film.

Evolution of the genomic systems of prokaryotes and its momentous consequences.

Abstract: The earliest self-reproducing cell on Earth, our common ancestor, was probably as small as present-day bacteria. It gave rise to a very large and durable clone whose descendants must have been the only living occupants of the oceans for about one thousand million years. They reached astronomical numbers of separate, disjunct cells, and synthesized many new genes. Their small volume could not accommodate ever larger genomes and useful new genes replaced resident, less successful sequences, thus increasing diversity and the number of strains with highly specialized, distinct, bioenergetic potentialities. Also, selective pressure favored strains able to participate successfully in division of labor and in the sharing of diverse abilities in mixed communities, counterbalancing the limited capacities of individual genomes. Lateral gene transfer mechanisms appeared and were progressively improved, furthering the development of diversity. The prokaryotes' constructive evolution resulted in the formation of a worldwide web of genetic information, and a global bacterial superbiosystem superorganism). By contrast, eukaryotic evolution of organisms has been typically Darwinian. Diversification of eukaryotic organisms was, however, considerably enriched and accelerated by symbioses with prokaryotes.The more broadly diversified bioenergetic potential of prokaryotes considerably increased the diversity of eukaryotes. Without their participation, our biosphere would have remained much less diverse and less dynamic. Environmental homeostasis has been maintained all along by guided bacterial evolution.

Exploring Leeuwenhoek's legacy: the abundance and diversity of protozoa.

Abstract: Towards the end of the 17th century, Leeuwenhoek built "magnifying glasses" that enabled him to see and describe protozoa for the first time. Continued exploration of the natural history of protozoa during the past 300 years has progressed far beyond simply documenting morphospecies (global total probably <20,000). We now realize that protozoan 'biodiversity' is multi-faceted (e.g. sibling species, variant genotypes and syntrophic consortia). Realization of their extraordinary abundance has secured for protozoa the position of dominant phagotrophs and regenerators of nutrients within microbial food webs. And studies of protozoa in the natural environment have done much to effect a paradigm shift in our understanding of why specific microbes live where they do and how they got there in the first place. In particular, the hypothesis of ubiquitous dispersal of protozoan species does seem to be supported by the evidence provided by morphospecies, sibling species and even individual genotypes.

Hydrophobicity and adhesion to fish cells and mucus of Vibrio strains isolated from infected fish.

Abstract: The hydrophobicity of 44 Vibrio strains isolated from cultured, diseased gilt-head sea bream (Sparus aurata) was determined. Three different methods were used: (1) microbial adhesion to hydrocarbons (MATH), either with phosphate buffer or with phosphate urea magnesium sulfate (PUM) buffer, (2) aggregation in the presence of salt solutions (SAT), and (3) adhesion to nitrocellulose filters (NCF). The results show that experimental conditions exerted a significant influence on hydrophobicity. Thus, Kendall rank coefficients showed the presence of correlation only for SAT and NCF, and for SAT and the MATH assay with PUM buffer. Moreover, no relationships were observed between the bacterial hydrophobicity estimated with the methods mentioned above and the ability of the strains to adhere to fish mucus or cells. These results indicate that adhesion of pathogenic Vibrio strains to host surfaces is mediated mainly by specific receptor interactions, instead of by hydrophobic interactions.

The eaeA gene is not found in Hafnia alvei from patients with diarrhea in Aragón, Spain.

Abstract: A total of 102 Hafnia alvei clinical strains isolated from different patients with diarrhea has been tested, using polymerase chain reaction and dot-blot hybridization, for the enteropathogenic Escherichia coli attaching and effacing A (eaeA) gene to establish their role as a causative agent of diarrhea in our environment None of them was positive for the eaeA gene We cannot consider the eaeA gene as the virulence-associated factor implicated in the H alvei strains isolated from diarrheal feces in our region

Unusual characteristics of ciliate actins.

Abstract: Actin is a cytoskeletal protein that is ubiquitous in eukaryotes, hence the corresponding genes and proteins have been isolated from numerous organisms as different as animals, plants, fungi and protozoa. Several atomic models are available for the monomeric as well as the filamentous form, and more than 70 proteins that bind actin and control filament dynamics have been isolated from diverse eukaryotes. Moreover, the function and dynamics of the actin cytoskeleton in several eukaryotic systems have been depicted in depth. Unlike other protozoa, such as amoeba, actin is not an abundant protein in ciliates, whose cytoskeleton is mainly composed of microtubular arrays. Ciliate actin has been studied in several species, and it was established early on that this ciliate protein is very different from that of other eukaryotes. Similarly, the actin-binding proteins studied in ciliates display great differences with those of other eukaryotes. Consequently, ciliate actin has been considered as "unconventional," and this review focuses on molecular data leading to this conclusion.

Adaptation of bacterial communities to environmental transitions from labile to refractory substrates.

Abstract: The aim of this work was to assess the adaptation of bacterial communities to environmental transitions from labile to refractory substrates. This involved testing the hypothesis that bacteria self-organize and propagate not only as individual cellular systems, but also as functional sets of interacting organisms. A biofilm community was cultivated in a flow-cell irrigated with tryptic soy broth and subjected to a cyclic series of environmental transitions, from labile to refractory substrates, followed by a period of starvation (30 days). The appearance and disappearance of specific colony morphotypes when the emigrants were plated onto tryptic soy agar was used to monitor the restructuring of the community. Confocal laser microscopy of flow cells showed that these transitions decreased the biofilm thickness and coverage. Substrate shifts also changed the architecture of the biofilm communities. Repeated inoculation of flow-cell communities with a composite inoculum increased the number and diversity of emigrants. Their biofilms were thicker and covered a wider area than those of communities that had been inoculated only at the beginning of the experiment. With repeated inoculation, the time required for the community to restructure and stabilize decreased during most transitions. This suggested that organismal recombination acted as a mechanism of adaptation, enhancing the growth of microbial communities exposed to environmental stresses. Changes in the profiles of emigrants during the adaptation of biofilm communities to environmental transitions showed the appearance and disappearance of discrete sets of organisms. This suggested that the biofilm communities responded to environmental stresses as sets of interacting organisms. Enhanced growth of biofilm communities due to repeated environmental cycling suggested that the functionality of cellular positioning accrued from one cycle to the next and was thus heritable, although it was not necessarily genetically encoded.

Production of phenolics by immobilized cells of the lichen Pseudevernia furfuracea: the role of epiphytic bacteria

Abstract: Immobilized lichen cells from the thalli of the lichen Pseudevernia furfuracea, supplied with acetate as the only source of carbon, continuously produced phenolic substances, atranorin and physodic acid, over 23 days. Epiphytic bacteria associated with the lichen thallus grew actively, probably using both acetate and reduced compounds supplied by lichen cells, since their active growth was avoided by including 10 microM 3,3'-dichlorophenyl-1,1'dimethylurea in the bath solution. Penicillin largely impeded the growth of epiphytic bacteria and decreased phenolic production, which was recovered only at the end of the experimental period, just when the bacteria started a slow, but active growth. We suggest the cooperation of epiphytic bacteria in the biosynthesis of both atranotrin and physodic acid.

Susceptibility of motile and cystic forms of Borrelia burgdorferi to ranitidine bismuth citrate.

Abstract: Gastrointestinal symptoms accompanying Lyme disease have not been considered in the treatment of Lyme patients yet. Here we examine the effect of ranitidine bismuth citrate (RBC) on motile and cystic forms of Borrelia burgdorferi in vitro, to determine whether it could cure this bacterial infection in the gastrointestinal tract. When motile forms of B. burgdorferi were exposed to RBC for 1 week at 37 degrees C, the minimal bactericidal concentration (MBC) was > 64 mg/ml. At 30 degrees C, the MBC was > 256 mg/ml. When the incubation lasted for 2 weeks at 37 degrees C, the MBC dropped to > 2 mg/ml. Bismuth aggregates were present on the surface of B. burgdorferi when RBC > or = MBC, as shown by transmission electron microscopy (TEM). Cystic forms of B. burgdorferi, exposed to RBC for 2 weeks at 37 degrees C, were examined by cultivation in BSK-H medium (Sigma B3528). They were stained with acridine orange (pH 6.4, pH 7.4) and studied by TEM. The MBC for RBC for young cystic forms (1 day old) and old cysts (8 months old) was estimated to be > 0.125 mg/ml and > 2 mg/ml, respectively. Bismuth aggregates were attached to the cysts and, in some, the pin-shaped aggregates penetrated the cyst wall. The bismuth aggregates also bound strongly to blebs and granules of B. burgdorferi when RBC > or = MBC. When B. burgdorferi is responsible for gastrointestinal symptoms, bismuth compounds may be candidates for eradication of the bacterium from the gastrointestinal tract.