Genome Evolution in the Obligate but Environmentally Active Luminous Symbionts of Flashlight Fish.

The luminous bacterial symbionts of anomalopid flashlight fish are thought to be obligately dependent on their hosts for growth and share several aspects of genome evolution with unrelated obligate symbionts, including genome reduction. However, in contrast to most obligate bacteria, anomalopid symbionts have an active environmental phase that may be important for symbiont transmission. Here we investigated patterns of evolution between anomalopid symbionts compared with patterns in free-living relatives and unrelated obligate symbionts to determine if trends common to obligate symbionts are also found in anomalopid symbionts. Two symbionts, "Candidatus Photodesmus katoptron" and "Candidatus Photodesmus blepharus," have genomes that are highly similar in gene content and order, suggesting genome stasis similar to ancient obligate symbionts present in insect lineages. This genome stasis exists in spite of the symbiont's inferred ability to recombine, which is frequently lacking in obligate symbionts with stable genomes. Additionally, we used genome comparisons and tests of selection to infer which genes may be particularly important for the symbiont's ecology compared with relatives. In keeping with obligate dependence, substitution patterns suggest that most symbiont genes are experiencing relaxed purifying selection compared with relatives. However, genes involved in motility and carbon storage, which are likely to be used outside the host, appear to be under increased purifying selection. Two chemoreceptor chemotaxis genes are retained by both species and show high conservation with amino acid sensing genes, suggesting that the bacteria may actively seek out hosts using chemotaxis toward amino acids, which the symbionts are not able to synthesize.

Microbial Population of the Digestive Tract of Click Beetle Larvae (Elateridae, Coleoptera).

The composition and functional structure of the intestinal microflora of three wireworm species (Agriotes obscurus (L.), Selatosomus aeneus (L.), and Ampedus pomorum (Herbst)) with different dietary regimes were studied. The total abundance of the microorganisms was evaluated by fluorescent microscopy, the group composition was assessed by inoculation on a solid glucose-peptone-yeast medium, and the functional diversity was estimated by multisubstrate testing. It was noted that, in the intestine of the larvae, the total number of microorganisms was lower by 1-2 orders of magnitude than in the soil and decaying wood. It was found that the composition of the intestinal microbial communities of wireworms was radically different from that of the substrate: the Bray-Curtis coefficient did not exceed 0.25. It was found that native forms accounted for more than half of the total number of saprotrophic bacteria: in the larvae, gram-positive cocci, enterobacteria, Vibrionaceae, Acinetobacter, and some genera of coryneform bacteria, which were absent in the soil and wood, prevailed. The micromycetes were either absent (Agriotes) or were found in insignificant quantities (Selatosomus, Ampedus). In Selatosomus, apart from the intestinal forms, representatives of Mezorhizobium, No- cardioides, and Erwinia, occurring on plant substrates, were observed.

Small RNAs in the Vibrionaceae: an ocean still to be explored.

In bacteria, the discovery of noncoding small RNAs (sRNAs) as modulators of gene expression in response to environmental signals has brought new insights into bacterial gene regulation, including control of pathogenicity. The Vibrionaceae constitute a family of marine bacteria of which many are responsible for infections affecting not only humans, such as Vibrio cholerae but also fish and marine invertebrates, representing the major cause of mortality in farmed marine species. They are able to colonize many habitats, existing as planktonic forms, in biofilms or associated with various hosts. This high adaptability is linked to their capacity to generate genetic diversity, in part through lateral gene transfer, but also by varying gene expression control. In the recent years, several major studies have illustrated the importance of small regulatory sRNAs in the Vibrionaceae for the control of pathogenicity and adaptation to environment and nutrient sources such as chitin, especially in V. cholerae and Vibrio harveyi. The existence of a complex regulatory network controlled by quorum sensing has been demonstrated in which sRNAs play central roles. This review covers major advances made in the discovery and elucidation of functions of Vibrionaceae sRNAs within the last 10 years.

Grimontia indica AK16(T), sp. nov., isolated from a seawater sample reports the presence of pathogenic genes similar to Vibrio genus.

Grimontia indica strain AK16(T) sp. nov. is the type strain of G. indica sp. nov. a new species within the genus Grimontia. This strain, whose genome is described here, was isolated from seawater sample collected from southeast coast of Palk Bay, India. G. indica AK16(T) is a Gram-negative, facultative aerobic rod shaped bacterium. There are only two other strains in the genus Grimontia one of which, Grimontia hollisae CIP 101886(T), is a reported human pathogen isolated from human stool sample while the other, 'Grimontia marina IMCC5001(T)', was isolated from a seawater sample. As compared to the pathogenic strain Grimontia hollisae CIP 101886(T), the strain AK16(T) lacks some genes for pathogenesis like the accessory colonization factors AcfA and AcfD, which are required for the colonization of the bacterium in the host body. While it carries some pathogenesis genes like OmpU, which are related to pathogenesis of Vibrio strains. This suggests that the life cycle of AK16(T) may include some pathogenic interactions with marine animal(s), or it may be an opportunistic pathogen. Study of the Grimontia genus is important because of the severe pathogenic traits exhibited by a member of the genus with only three species reported in total. The study will provide some vital information which may be useful in future clinical studies on the genus.

Genes similar to the Vibrio parahaemolyticus virulence-related genes tdh, tlh, and vscC2 occur in other vibrionaceae species isolated from a pristine estuary.

Detection of the human pathogen Vibrio parahaemolyticus often relies on molecular biological analysis of species-specific virulence factor genes. These genes have been employed in determinations of V. parahaemolyticus population numbers and the prevalence of pathogenic V. parahaemolyticus strains. Strains of the Vibrionaceae species Photobacterium damselae, Vibrio diabolicus, Vibrio harveyi, and Vibrio natriegens, as well as strains similar to Vibrio tubiashii, were isolated from a pristine salt marsh estuary. These strains were examined for the V. parahaemolyticus hemolysin genes tdh, trh, and tlh and for the V. parahaemolyticus type III secretion system 2α gene vscC2 using established PCR primers and protocols. Virulence-related genes occurred at high frequencies in non-V. parahaemolyticus Vibrionaceae species. V. diabolicus was of particular interest, as several strains were recovered, and the large majority (>83%) contained virulence-related genes. It is clear that detection of these genes does not ensure correct identification of virulent V. parahaemolyticus. Further, the occurrence of V. parahaemolyticus-like virulence factors in other vibrios potentially complicates tracking of outbreaks of V. parahaemolyticus infections.

Comparative genomics of the family Vibrionaceae reveals the wide distribution of genes encoding virulence-associated proteins.

BACKGROUND: Species of the family Vibrionaceae are ubiquitous in marine environments. Several of these species are important pathogens of humans and marine species. Evidence indicates that genetic exchange plays an important role in the emergence of new pathogenic strains within this family. Data from the sequenced genomes of strains in this family could show how the genes encoded by all these strains, known as the pangenome, are distributed. Information about the core, accessory and panproteome of this family can show how, for example, genes encoding virulence-associated proteins are distributed and help us understand how virulence emerges. RESULTS: We deduced the complete set of orthologs for eleven strains from this family. The core proteome consists of 1,882 orthologous groups, which is 28% of the 6,629 orthologous groups in this family. There were 4,411 accessory orthologous groups (i.e., proteins that occurred in from 2 to 10 proteomes) and 5,584 unique proteins (encoded once on only one of the eleven genomes). Proteins that have been associated with virulence in V. cholerae were widely distributed across the eleven genomes, but the majority was found only on the genomes of the two V. cholerae strains examined. CONCLUSIONS: The proteomes are reflective of the differing evolutionary trajectories followed by different strains to similar phenotypes. The composition of the proteomes supports the notion that genetic exchange among species of the Vibrionaceae is widespread and that this exchange aids these species in adapting to their environments.

The genomic code: inferring Vibrionaceae niche specialization.

The Vibrionaceae show a wide range of niche specialization, from free-living forms to those attached to biotic and abiotic surfaces, from symbionts to pathogens and from estuarine inhabitants to deep-sea piezophiles. The existence of complete genome sequences for closely related species from varied aquatic niches makes this group an excellent case study for genome comparison.

Cloning of a crustin-like, single whey-acidic-domain, antibacterial peptide from the haemocytes of the European lobster, Homarus gammarus, and its response to infection with bacteria.

Degenerate PCR was used to isolate a 221-base pair nucleotide sequence of a new crustin-like antibacterial peptide from the haemocytes of the European lobster, Homarus gammarus. Rapid amplification of cDNA ends was used to extend the sequence to determine the complete open reading frame and un-translated regions. The inferred amino acid sequence of this peptide was found to be similar to crustin-like peptides isolated for several species of shrimp as well as the shore crab, Carcinus maenas. The sequence also contains a single-whey-acidic protein (WAP) domain, similar to novel antibacterial single-whey-acidic domain (SWD) peptides that have been recently described in the tiger shrimp, Penaeus monodon, and the Pacific white shrimp, Litopenaeus vannamei. Real-time PCR was used to analyse the expression of the gene coding for this peptide. The gene is up regulated after inoculation with the Gram-positive lobster pathogen Aerococcus viridans var. homari but down regulated after inoculation with the Gram-negative bacteria Listonella anguillarum. Phylogenetic analysis of this new peptide shows that it is most related to other antimicrobial crustin peptides and that the crustins are only distantly related to the antibacterial SWD peptides recently described.

Immunocompetence of juvenile chinook salmon against Listonella anguillarum following dietary exposure to polycyclic aromatic hydrocarbons.

Juvenile chinook salmon (Oncorhynchus tschawytscha) were fed a mixture of 14 polycyclic aromatic hydrocarbon (PAH) compounds that reflected the PAH composition of salmon stomach contents in an urban estuary of Puget Sound, Washington (USA). Following a 28-d dietary exposure, a standardized Listonella anguillarum challenge model was used to determine whether PAH exposure (16, 64, and 252 mg/kg wet wt feed) causes reduced disease resistance under the conditions examined in this study. To assess innate immunity, five replicate groups of fish per dose were acclimated for one week, exposed to a lethal concentration 60 of bacteria, and monitored for 14 d. In a parallel experiment, the effects of PAH exposure on the acquired immune response were examined by immersion vaccinating fish against L. anguillarum and allowing specific immunity to develop for three weeks prior to challenge. All mortalities were aseptically sampled to confirm L. anguillarum infections. No significant differences in fish length, weight, or coefficient of condition were observed. These controlled laboratory experiments suggest that dietary exposures to an environmentally relevant mixture of PAH compounds do not alter the immunocompetence or growth of juvenile chinook salmon.

Diseases of the eye of farmed shrimp Penaeus monodon.

Lesions were found in the eyes of cultured shrimp Penaeus monodon that displayed non-specific signs of disease, including lethargy, dark pigmentation, brown gills, empty midgut, anorexia, white tail muscle, necrosis of uropods and fouled cuticle. Eye lesions were associated with sexual development in moribund shrimp in at least 1 disease event. Suppurative inflammation, granuloma and malacia were observed in histological examination of the eye and the causative agents of lesions appear to be Vibrio spp. and a rod-shaped virus (similar to Lymphoid Organ Virus, Gill-Associated Virus [GAV] and Yellow-Head Virus). Suppurative inflammation was characterised by edema, infiltration of haemocytes and local sites of abscesses. Eyes with granuloma usually appeared white in pond-side examinations, and histology showed that fibrous tissue replaced ommatidia, ganglia and internal structures of the eye. Malacia of the eye was characterised by necrosis of nervous tissue, vacuolation and vascular proliferation in the medulla ganglia. Levels of presumptive Vibrionaceace were high in moribund specimens and Gram-negative rods were observed in some specimens as free particles in the interstitial fluid and haemolymph in the eye. Transmission electron microscopy showed that nerve cells in the fasciculated zone (near the basement membrane) contained cytoplasmic vesicles (1 to 3 microm in diameter) with particles (15 to 26 nm in diameter) and rod-shaped nucleocapsids. The rods were similar to those of GAV and were 130 to 260 nm long, 10 to 16 nm in diameter and had helical symmetry with a screw-like thread (2.4 to 3.5 nm pitch). Also, unidentified enveloped virions, averaging 74 nm in diameter, were observed in cytoplasmic vesicles in the fasciculated zone. In conclusion, it is suggested that bacterial and viral infections of the eye could result in impaired neuroendocrine functions, which may cause a range of clinical signs of disease.

Identificación de bacilos gramnegativos, anaerobios facultativos, oxidasas positivos / Identification of Gram-negative, facultatively anaerobie, oxidase-positive bacilli

Se realizó la identificación de 100 cepas de bacilos gramnegativos, anaerobios facultativos, oxidasas positivos, aisladas de diferentes productos patológicos humanos por métodos bioquímicos convencionales. Del total de las cepas estudiadas 1 correspondió al genero Vibrio, 66 al género Aeromonas y 33 al género Plesiomonas. Se destaca la importancia de establecer estudios de vigilancia de estos microorganismos para investigar su circulación en nuestro medio.

Identificación de bacilos gramnegativos, anaerobios facultativos, oxidasas positivos / Identification of Gram-negative, facultatively anaerobie, oxidase-positive bacilli

Se realizó la identificación de 100 cepas de bacilos gramnegativos, anaerobios facultativos, oxidasas positivos, aisladas de diferentes productos patológicos humanos por métodos bioquímicos convencionales. Del total de las cepas estudiadas 1 correspondió al genero Vibrio, 66 al género Aeromonas y 33 al género Plesiomonas. Se destaca la importancia de establecer estudios de vigilancia de estos microorganismos para investigar su circulación en nuestro medio

Plesiomonas shigelloides--associated diarrhea.

Although Plesiomonas shigelloides is considered to be a cause of diarrhea in the Orient, it has infrequently been noted to be associated with diarrhea in Taiwan. Six cases of various extent of diarrhea were found to be associated with P. shigelloides in stool culture in this department between January 1987 and December 1988. Only two of them had history of chronic diarrhea and the others had mild or even no symptom. All six strains of this organism were susceptible to most commonly used antibiotics, but resistant to ampicillin, carbenicillin, clindamycin, oxacillin, penicillin, and vancomycin. Those which required least minimal inhibitory concentration (MIC) were cefazolin, ceftazidime, cefuroxime, ciprofloxacin, and trimethoprim/sulfamethoxazole. Our experiences showed that P. shigelloides may cause mild diarrhea in normal hosts. It sometimes is an incidental finding. An oxidase test for this organism should be included as routine culture of the stool specimen, but treatment is not always necessary.

Aeromonas and Plesiomonas as food- and waterborne pathogens.

Aeromonas and Plesiomonas have become increasingly recognized as human enteropathogens. Plesiomonas shigelloides has mainly been recovered from various sea foods, whereas Aeromonas sp. have also been cultured from pigs, broilers, eggs, milk and vegetables. Aeromonas sp. also multiply rapidly at +4 degrees C which is a significant risk in food storage. Aeromonas sp. have furthermore been recovered from fresh water sources, and some isolates are resistant to chlorination which makes it a further risk factor. No large food- or waterborne outbreaks have been reported so far with Aeromonas sp. Various virulence factors involved in intestinal infections are described such as enterotoxins, cytotoxins, and adhesins.