Biomedical subjects

Eugene Rosenberg

Publications and source records attributed to Eugene Rosenberg.

16 recordsLinked to original sources

PubMed2007

Culturable and VBNC Vibrio cholerae: interactions with chironomid egg masses and their bacterial population.

Vibrio cholerae, the etiologic agent of cholera, is autochthonous to various aquatic environments. Recently, it was found that chironomid (nonbiting midges) egg masses serve as a reservoir for the cholera bacterium and that flying chironomid adults are possible windborne carriers of V. cholerae non-O1 non-O139. Chironomids are the most widely distributed insect in freshwater. Females deposit egg masses at the water's edge, and each egg mass contains eggs embedded in a gelatinous matrix. Hemagglutinin/protease, an extracellular enzyme of V. cholerae, was found to degrade chironomid egg masses and to prevent them from hatching. In a yearly survey, chironomid populations and the V. cholerae in their egg masses followed phenological succession and interaction of host-pathogen population dynamics. In this report, it is shown via FISH technique that most of the V. cholerae inhabiting the egg mass are in the viable but nonculturable (VBNC) state. The diversity of culturable bacteria from chironomid egg masses collected from two freshwater habitats was determined. In addition to V. cholerae, representatives of the following genera were isolated: Acinetobacter, Aeromonas, Klebsiella, Shewanella, Pseudomonas, Paracoccus, Exiguobacterium, and unidentified bacteria. Three important human pathogens, Aeromonas veronii, A. caviae, and A. hydrophila, were isolated from chironomid egg masses, indicating that chironomid egg masses may be a natural reservoir for pathogenic Aeromonas species in addition to V. cholerae. All isolates of V. cholerae were capable of degrading chironomid egg masses. This may help explain their host-pathogen relationship with chironomids. In contrast, almost none of the other bacteria that were isolated from the egg masses possessed this ability. Studying the interaction between chironomid egg masses, the bacteria inhabiting them, and V. cholerae could contribute to our understanding of the nature of the V. cholerae-egg mass interactions.

Animals↗

PubMed2006

The Acinetobacter outer membrane protein A (OmpA) is a secreted emulsifier.

Acinetobacter strains use hydrophobic carbon sources and most of them are efficient oil degraders. They secrete a variety of emulsifiers which are efficient in producing and stabilizing oil-in-water emulsions. The bioemulsifier of Acinetobacter radioresistens KA53 (Alasan) is a high-mass complex of proteins and polysaccharides. The major emulsification activity of this complex is associated with a 45 kDa protein (AlnA), which is homologous to the outer membrane protein OmpA. The emulsification ability of AlnA depends on the presence of hydrophobic residues in the four loops spanning the transmembrane domains. The finding of a secreted OmpA was unexpected, in view of the fact that this protein is essential in all Gram-negative bacteria, has four trans-membrane domains and is considered to be an integral structural component of the outer membrane. However, secretion of an OmpA with emulsifying ability could be of physiological importance in the utilization of hydrophobic substrates as carbon sources. Here we examined the possibility that secretion of OmpA with emulsifying activity is a general property of the oil-degrading Acinetobacter strains. The results indicate that OmpA is secreted in five strains of Acinetobacter, including strain Acinetobacter sp. ADP1 whose genome has been sequenced. The ompA genes of ADP1 and an additional strain, Acinetobacter sp. V-26 were cloned and sequenced. Structure analysis of the sequence of the two proteins indicated the existence of the hydrophobic regions, previously shown to be responsible for the emulsification activity of AlnA. Further examination of the recombinant OmpA proteins indicated that they are, indeed, strong emulsifiers, even when produced in Escherichia coli. The finding that Acinetobacter OmpA has emulsifying activity and that it is secreted in five strains of Acinetobacter may be physiologically significant and suggests the involvement of this protein in biodegradation of hydrophobic substrates, including hydrocarbons.

Acinetobacter↗

PubMed2006

The coral probiotic hypothesis.

Emerging diseases have been responsible for the death of about 30% of corals worldwide during the last 30 years. Coral biologists have predicted that by 2050 most of the world's coral reefs will be destroyed. This prediction is based on the assumption that corals can not adapt rapidly enough to environmental stress-related conditions and emerging diseases. Our recent studies of the Vibrio shiloi/Oculina patagonica model system of the coral bleaching disease indicate that corals can indeed adapt rapidly to changing environmental conditions by altering their population of symbiotic bacteria. These studies have led us to propose the Coral Probiotic Hypothesis. This hypothesis posits that a dynamic relationship exists between symbiotic microorganisms and environmental conditions which brings about the selection of the most advantageous coral holobiont. Changing their microbial partners would allow the corals to adapt to changing environmental conditions more rapidly (days to weeks) than via mutation and selection (many years). An important outcome of the Probiotic Hypothesis would be development of resistance of the coral holobiont to diseases. The following evidence supports this hypothesis: (i) Corals contain a large and diverse bacterial population associated with their mucus and tissues; (ii) the coral-associated bacterial population undergoes a rapid change when environmental conditions are altered; and (iii) although lacking an adaptive immune system (no antibodies), corals can develop resistance to pathogens. The Coral Probiotic Hypothesis may help explain the evolutionary success of corals and moderate the predictions of their demise.

Adaptation, Physiological↗

PubMed2006

Bacteria associated with mucus and tissues of the coral Oculina patagonica in summer and winter.

The relative abundance of bacteria in the mucus and crushed tissue of the Mediterranean coral Oculina patagonica was determined by analyses of the 16S rRNA genes of isolated colonies and from a 16S rRNA clone library of extracted DNA. By SYBR gold staining, the numbers of bacteria in mucus and tissue samples were 6.2 x 10(7) and 8.3 x 10(8)/cm2 of coral surface, respectively, 99.8% of which failed to produce colonies on Marine Agar. From analysis of mucus DNA, the most-abundant bacterium was Vibrio splendidus, representing 68% and 50% of the clones from the winter and summer, respectively. After removal of mucus from coral by centrifugation, analyses of DNA from the crushed tissue revealed a large diversity of bacteria, with Vibrio species representing less than 5% of the clones. The most-abundant culturable bacteria were a Pseudomonas sp. (8 to 14%) and two different alpha-proteobacteria (6 to 18%). Out of a total 1,088 16S rRNA genes sequenced, 400 different operational taxonomic units were identified (> 99.5% identity). Of these, 295 were novel (< 99% identical to any sequences in the GenBank database). This study provides a comprehensive database for future examinations of changes in the bacterial community during bleaching events.

Animals↗

PubMed2005

The diversity of bacterial pathogenicity mechanisms.

A report on the international conference 'Molecular basis of bacterial pathogenesis', sponsored by the Federation of European Microbiological Societies (FEMS) and the Israel Center for the Study of Emerging Diseases, Ein Gedi, Israel, 23-27 January 2005.

Bacteria↗

PubMed2004

The Vibrio shiloi/Oculina patagonica model system of coral bleaching.

The scleractinian coral Oculina patagonica undergoes bleaching (loss of its endosymbiotic zooxanthellae) every summer in the eastern Mediterranean Sea when seawater temperatures rise. The causative agent of the disease is Vibrio shiloi. The pathogen adheres to a beta-galactoside-containing receptor in the coral mucus, penetrates into epithelial cells, differentiates into a viable-but-not-culturable form, multiplies, and produces a proline-rich peptide toxin that inhibits photosynthesis of the zooxanthellae in the presence of ammonia. Several of the virulence factors, such as adhesin, toxin, and superoxide dismutase, are produced only at the elevated summer seawater temperatures. The fireworm Hermodice carunculata is a winter reservoir and spring/summer vector for V. shiloi. The generality of the bacterial hypothesis of coral bleaching is discussed.

Animals↗

PubMed2003

Superoxide dismutase is a virulence factor produced by the coral bleaching pathogen Vibrio shiloi.

Coral bleaching is a disease that threatens coral reefs throughout the world. The disease is correlated with higher-than-normal seawater temperatures. Data have been reported showing that bleaching of the coral Oculina patagonica during the summer in the Mediterranean Sea is the result of an infection with Vibrio shiloi. The summer temperatures induce the expression of virulence factors in the pathogen. We report here that V. shiloi produces an extracellular superoxide dismutase (SOD) at 30 degrees C, but not at 16 degrees C. An SOD(-) mutant was avirulent. The mutant adhered to corals, penetrated into coral cells, multiplied intracellularly for a short time, and then died. These data support the hypothesis that SOD protects the intracellular V. shiloi from oxidative stress caused by the high concentration of oxygen produced by intracellular zooxanthellae photosynthesis.

Anthozoa↗

PubMed2003

The marine fireworm Hermodice carunculata is a winter reservoir and spring-summer vector for the coral-bleaching pathogen Vibrio shiloi.

Vibrio shiloi, the causative agent of bleaching of the coral Oculina patagonica in the Mediterranean Sea, is present in all bleached O. patagonica corals in the summer (25-30 degrees C), but can be not detected in the coral during the winter (16-20 degrees C). Furthermore, the pathogen can not survive in O. patagonica at temperatures below 20 degrees C. Using fluorescence in situ hybridization (FISH) with a V. shiloi-specific oligonucleotide probe, we found that the marine fireworm Hermodice caranculata is a winter reservoir for V. shiloi. Worms taken directly from the sea during the winter contained approximately 10(8) V. shiloi per worm by FISH analysis. However, colony-forming units (cfu) revealed only 4.1-18.3 x 10(4) V. shiloi per worm, indicating that approximately 99.9% of them were in the viable-but-not-culturable (VBNC) state. When worms were infected with V. shiloi, most of the bacteria adhered to the worm within 24 h and then penetrated into epidermal cells. By 48 h, less than 10(-4) of the intact V. shiloi in the worm gave rise to colonies, suggesting that they differentiated inside the worm into the VBNC state. When worms infected with V. shiloi were placed in aquaria containing O. patagonica, all of the corals showed small patches of bleached tissue in 7-10 days and total bleaching in 17 days. This is the first report of a reservoir and vector for a coral disease.

Animals↗

PubMed2003

Petroleum pollution bioremediation using water-insoluble uric acid as the nitrogen source.

The biodegradation of hydrocarbon pollutants in open systems is limited by the availability of a utilizable nitrogen source. This limitation can be overcome by using uric acid. Enrichment cultures grown on crude oil-uric acid media yielded mixed and pure cultures that degraded petroleum. In a simulated open system, uric acid bound to crude oil and was available for bacterial growth and petroleum biodegradation.

Acinetobacter↗

PubMed2003

Temperature-regulated bleaching and lysis of the coral Pocillopora damicornis by the novel pathogen Vibrio coralliilyticus.

Coral bleaching is the disruption of symbioses between coral animals and their photosynthetic microalgal endosymbionts (zooxanthellae). It has been suggested that large-scale bleaching episodes are linked to global warming. The data presented here demonstrate that Vibrio coralliilyticus is an etiological agent of bleaching of the coral Pocillopora damicornis. This bacterium was present at high levels in bleached P. damicornis but absent from healthy corals. The bacterium was isolated in pure culture, characterized microbiologically, and shown to cause bleaching when it was inoculated onto healthy corals at 25 degrees C. The pathogen was reisolated from the diseased tissues of the infected corals. The zooxanthella concentration in the bacterium-bleached corals was less than 12% of the zooxanthella concentration in healthy corals. When P. damicornis was infected with V. coralliilyticus at higher temperatures (27 and 29 degrees C), the corals lysed within 2 weeks, indicating that the seawater temperature is a critical environmental parameter in determining the outcome of infection. A large increase in the level of the extracellular protease activity of V. coralliilyticus occurred at the same temperature range (24 to 28 degrees C) as the transition from bleaching to lysis of the corals. We suggest that bleaching of P. damicornis results from an attack on the algae, whereas bacterium-induced lysis and death are promoted by bacterial extracellular proteases. The data presented here support the bacterial hypothesis of coral bleaching.

Amino Acid Sequence↗

PubMed2002

Biosurfactants and oil bioremediation.

Oil pollution is an environmental problem of increasing importance. Hydrocarbon-degrading microorganisms, adapted to grow and thrive in oil-containing environments, have an important role in the biological treatment of this pollution. One of the limiting factors in this process is the bioavailability of many fractions of the oil. The hydrocarbon-degrading microorganisms produce biosurfactants of diverse chemical nature and molecular size. These surface-active materials increase the surface area of hydrophobic water-insoluble substrates and increase their bioavailability, thereby enhancing the growth of bacteria and the rate of bioremediation.

Bacteria↗

PubMed2002

Structure--function studies of the recombinant protein bioemulsifier AlnA.

Acinetobacter radioresistens KA53 produces an extracellular bioemulsifier, referred to as alasan. The surface active component of alasan is a 35.77 kDa protein AlnA. Although AlnA and the Escherichia coli outer membrane protein A (OmpA) have a high amino acid sequence homology, E. coli OmpA has no emulsifying activity. Comparison of the amino acid sequences of AlnA and E. coli OmpA revealed four hydrophobic regions in AlnA that were absent in E. coli OmpA. Deletions and substitutions (with the homologous OmpA sequence) were constructed in each of the four hydrophobic regions of AlnA by site-directed polymerase chain reaction (PCR) mutagenesis, using the overlap PCR method. Analysis of the emulsifying activities of the mutated AlnA molecules demonstrated that all four hydrophobic regions were necessary for emulsifying activity. However, most of the inactive mutated proteins still adhered avidly to hexadecane. These findings indicate that in addition to binding to hydrocarbons, the protein emulsifier must form a specific structure on the surface of the hydrocarbon that prevents coalescence of oil droplets. This is the first structure-function study of a protein bioemulsifer.

Acinetobacter↗

PubMed2002

Microbial diseases of corals and global warming.

Coral bleaching and other diseases of corals have increased dramatically during the last few decades. As outbreaks of these diseases are highly correlated with increased sea-water temperature, one of the consequences of global warming will probably be mass destruction of coral reefs. The causative agent(s) of a few of these diseases have been reported: bleaching of Oculina patagonica by Vibrio shiloi; black band disease by a microbial consortium; sea-fan disease (aspergillosis) by Aspergillus sydowii; and coral white plague possibly by Sphingomonas sp. In addition, we have recently discovered that Vibrio coralyticus is the aetiological agent for bleaching the coral Pocillopora damicornis in the Red Sea. In the case of coral bleaching by V. shiloi, the major effect of increasing temperature is the expression of virulence genes by the pathogen. At high summer sea-water temperatures, V. shiloi produces an adhesin that allows it to adhere to a beta-galactoside-containing receptor in the coral mucus, penetrate into the coral epidermis, multiply intracellularly, differentiate into a viable-but-not-culturable (VBNC) state and produce toxins that inhibit photosynthesis and lyse the symbiotic zooxanthellae. In black band disease, sulphide is produced at the coral-microbial biofilm interface, which is probably responsible for tissue death. Reports of newly emerging coral diseases and the lack of epidemiological and biochemical information on the known diseases indicate that this will become a fertile area of research in the interface between microbial ecology and infectious disease.

Animals↗

PubMed2002

The active component of the bioemulsifier alasan from Acinetobacter radioresistens KA53 is an OmpA-like protein.

The bioemulsifier of Acinetobacter radioresistens KA53, referred to as alasan, is a high-molecular-weight complex of polysaccharide and protein. Recently, one of the alasan proteins, with an apparent molecular mass of 45 kDa, was purified and shown to constitute most of the emulsifying activity. The N-terminal sequence of the 45-kDa protein showed high homology to an OmpA-like protein from Acinetobacter spp. In the research described here the gene coding for the 45-kDa protein was cloned, sequenced, and expressed in Escherichia coli. Recombinant protein AlnA (35.77 kDa without the leader sequence) had an amino acid sequence homologous to that of E. coli OmpA and contained 70% of the specific (hydrocarbon-in-water) emulsifying activity of the native 45-kDa protein and 2.4 times that of the alasan complex. In addition to their emulsifying activity, both the native 45-kDa protein and the recombinant AlnA were highly effective in solubilizing phenanthrene, ca. 80 microg per mg of protein, corresponding to 15 to 19 molecules of phenanthrene per molecule of protein. E. coli OmpA had no significant emulsifying or phenanthrene-solubilizing activity. The production of a recombinant surface-active protein (emulsification and solubilization of hydrocarbons in water) from a defined gene makes possible for the first time structure-function studies of a bioemulsan.

Acinetobacter↗

PubMed1999

Genetic and functional analysis of genes required for the post-modification of the polyketide antibiotic TA of Myxococcus xanthus.

The antibiotic TA of Myxococcus xanthus is a complex macrocyclic polyketide, produced through successive condensations of acetate by a type I PKS (polyketide synthase) mechanism. The genes encoding TA biosynthesis are clustered on a 36 kb DNA fragment, which has been cloned and analysed. The chemical structure of TA and the mechanism by which it is synthesized indicate the need for several post-modification steps, which are introduced into the carbon chain of the polyketide to form the final bioactive molecule. These include the addition of several carbon atoms originating from acetate carbonyl, three C-methylations, O-methylation and a specific hydroxylation. This paper reports the analysis of five genes which are involved in the post-modification of TA. Their functional analysis, by specific gene disruption, suggests that they may be essential for the production of the active antibiotic. The characteristics and organization of the genes suggest that they may be involved in the addition of the carbon atoms which arise from acetate.

Amino Acid Sequence↗

PubMed1998

Molecular analysis of the DNA gyrB gene from Myxococcus xanthus.

DNA gyrase, an essential type II topoisomerase, mediates negative supercoiling of the bacterial chromosome, thereby affecting the processes of DNA replication, transcription, recombination and repair. The gyrB gene from the Gram-negative soil bacterium Myxococcus xanthus was sequenced. The sequence predicts a protein of 815 amino acid residues displaying significant homology to all known GyrB proteins. A 6-His-GyrB fusion protein was overexpressed in Escherichia coli and purified to near homogeneity using affinity chromatography on Ni-nitrilotriacetic acid-agarose and novobiocin-Sepharose columns. The fusion protein bound novobiocin and cross-reacted with anti-E. coli GyrB antibodies, indicating structural and functional similarities to the E. coli DNA GyrB. The gene was mapped to the region of the origin of replication (oriC) of M. xanthus.

Amino Acid Sequence↗