Phylogenetic Diversity of Bacterial Community Associated with the Marine Sponge Halichondira nigrocutis Collected off Southwest Indian Coast

This study aimed to evaluate the bacterial communities associated with the marine sponge Halichondria nigrocutis present in Indian waters by both cultivation and cultivation-independent techniques. Results using cultivation method showed that bacteria belonging to Bacillus, Acinetobacter and Vibrio spp. to be the predominant groups. Metagenomic study of sponge-associated bacteria by cultivation independent approach, involving cloning and sequencing of the 16S rDNA gene generated sequences that were subjected to phylogenetic analysis. Results demonstrated the community structure to be represented by the phyla Proteobacteria (alpha-, gamma- and delta-classes), Cyanobacteria, Actinobacteria and Firmicutes, with isolates belonging to alpha-proteobacterial group to be predominating. To our knowledge this study appears to be the first to record cultivable and uncultivable bacterial groups associated with H.nigrocutis from Indian waters

Expression and quorum sensing regulation of type III secretion system genes of <i>Vibrio harveyi</i> during infection of gnotobiotic brine shrimp

Type III secretion systems enable pathogens to inject their virulence factors directly into the cytoplasm of the host cells. The type III secretion system of Vibrio harveyi, a major pathogen of aquatic organisms and a model species in quorum sensing studies, is repressed by the quorum sensing master regulator LuxR. In this study, we found that during infection of gnotobiotic brine shrimp larvae, the expression levels of three type III secretion operons in V. harveyi increased within the first 12h after challenge and decreased again thereafter. The in vivo expression levels were highest in a mutant with a quorum sensing system that is locked in low cell density configuration (minimal LuxR levels) and lowest in a mutant with a quorum sensing system that is locked in the high cell density configuration (maximal LuxR levels), which is consistent with repression of type III secretion by LuxR. Remarkably, in vivo expression levels of the type III secretion system genes were much (> 1000 fold) higher than the in vitro expression levels, indicating that (currently unknown) host factors significantly induce the type III secretion system. Given the fact that type III secretion is energy-consuming, repression by the quorum sensing master regulators might be a mechanism to save energy under conditions where it does not provide an advantage to the cells

Expression of virulence genes in luminescent and nonluminescent isogenic vibrios and virulence towards gnotobiotic brine shrimp (<i>Artemia franciscana</i>)

Aims: This study aimed to evaluate the expression levels of virulence gene regulators (luxR and toxR) and virulence factors (serine protease, metalloprotease and haemolysin) in luminescent and nonluminescent isogenic Vibrio harveyi and Vibrio campbellii.Method and Results: Nonluminescent variants have been reported before to become dominant in cultures of luminescent vibrios when grown under static conditions in the dark. Wild-type V. harveyi BB120, V. campbellii LMG 21363, quorum sensing mutants of V. harveyi BB120 and their previously reported nonluminescent isogenic counterparts were used in this study. The expression level of the virulence genes srp serine protease, vhp metalloprotease and vhh haemolysin, the quorum sensing master regulator gene luxR and the virulence regulator gene toxR in isogenic luminescent and nonluminescent strains were quantified using reverse transcriptase real-time PCR. These experiments revealed that the nonluminescent strains produced lower levels of the quorum sensing master regulator gene luxR and the vhp metalloprotease gene (which is known to be regulated by quorum sensing). Finally, challenge tests with gnotobiotic brine shrimp (Artemia franciscana) larvae revealed that the nonluminescent strains are less virulent than their luminescent isogenic counterparts.Conclusion: Nonluminescent variants of V. harveyi and V. campbellii strains produce lower levels of the quorum sensing master regulator gene luxR and the vhp metalloprotease gene and are less virulent to brine shrimp than their isogenic luminescent counterparts.Significance and Impact of the study: These results indicate that adaptation of luminescent vibrios to specific growth conditions that result in a dominant nonluminescent phenotype is accompanied by a decreased adaptation to a host environment because of altered virulence gene regulation

Transporting ideas between marine and social sciences: experiences from interdisciplinary research programs.

The oceans comprise 70% of the surface area of our planet, contain some of the world’s richest natural resources and are one of the most significant drivers of global climate patterns. As the marine environment continues to increase in importance as both an essential resource reservoir and facilitator of global change, it is apparent that to find long-term sustainable solutions for our use of the sea and its resources and thus to engage in a sustainable blue economy, an integrated interdisciplinary approach is needed. As a result, interdisciplinary working is proliferating. We report here our experiences of forming interdisciplinary teams (marine ecologists, ecophysiologists, social scientists, environmental economists and environmental law specialists) to answer questions pertaining to the effects of anthropogenic-driven global change on the sustainability of resource use from the marine environment, and thus to transport ideas outwards from disciplinary confines. We use a framework derived from the literature on interdisciplinarity to enable us to explore processes of knowledge integration in two ongoing research projects, based on analyses of the purpose, form and degree of knowledge integration within each project. These teams were initially focused around a graduate program, explicitly designed for interdisciplinary training across the natural and social sciences, at the Gothenburg Centre for Marine Research at the University of Gothenburg, thus allowing us to reflect on our own experiences within the context of other multi-national, interdisciplinary graduate training and associated research programs

Regulation of virulence factors by quorum sensing in Vibrio harveyi.

Vibrio harveyi is an important aquatic pathogen that produces several virulence factors. In this study, the effect of quorum sensing, bacterial cell-to-cell communication, on the production of the virulence factors caseinase, gelatinase, lipase, hemolysin, and phospholipase, was investigated. The activity of virulence factors was studied through enzymatic plate assays using V. harveyi wild type and mutants with constitutively maximal or minimal quorum sensing activity. The results showed that quorum sensing negatively regulates phospholipase activity as higher activity was observed in mutants with minimal quorum sensing activity than in the mutant with maximal quorum sensing activity. Reverse transcriptase real-time PCR with specific primers revealed that the expression level of three phospholipase genes was 2-fold lower in the mutant with minimal quorum sensing activity than in the mutant with maximal quorum sensing activity. As far as we know, this is the first report of quorum sensing regulation of phospholipase. Finally, caseinase and gelatinase activity were positively regulated by quorum sensing, which is consistent with previous reports, and lipase and hemolysin activity were found to be independent of quorum sensing. Hence, the regulation is different for different virulence factors, with some being either positively or negatively regulated, and others being independent of quorum sensing. This might reflect the need to produce the different virulence factors at different stages during infection

Microbial community management in aquaculture

Microbial community management in aquaculture creates benefits at the nutritional as well as at health level for cultured species. In addition, in case of biofloc application, it allows to link species at different trophic levels, making bioflocs the potential link in integrated multispecies aquaculture

Inhibition of Fungi and Gram-Negative Bacteria by Bacteriocin BacTN635 Produced by Lactobacillus plantarum sp. TN635

The aim of this study was to evaluate 54 lactic acid bacteria (LAB) strains isolated from meat, fermented vegetables and dairy products for their capacity to produce antimicrobial activities against several bacteria and fungi. The strain designed TN635 has been selected for advanced studies. The supernatant culture of this strain inhibits the growth of all tested pathogenic including the four Gram-negative bacteria (Salmonella enterica ATCC43972, Pseudomonas aeruginosa ATCC 49189, Hafnia sp. and Serratia sp.) and the pathogenic fungus Candida tropicalis R2 CIP203. Based on the nucleotide sequence of the 16S rRNA gene of the strain TN635 (1,540 pb accession no FN252881) and the phylogenetic analysis, we propose the assignment of our new isolate bacterium as Lactobacillus plantarum sp. TN635 strain. Its antimicrobial compound was determined as a proteinaceous substance, stable to heat and to treatment with surfactants and organic solvents. Highest antimicrobial activity was found between pH 3 and 11 with an optimum at pH = 7. The BacTN635 was purified to homogeneity by a four-step protocol involving ammonium sulfate precipitation, centrifugal microconcentrators with a 10-kDa membrane cutoff, gel filtration Sephadex G-25, and C18 reverse-phase HPLC. SDS-PAGE analysis of the purified BacTN635, revealed a single band with an estimated molecular mass of approximately 4 kDa. The maximum bacteriocin production (5,000 AU/ml) was recorded after a 16-h incubation in Man, Rogosa, and Sharpe (MRS) medium at 30 °C. The mode of action of the partial purified BacTN635 was identified as bactericidal against Listeria ivanovii BUG 496 and as fungistatic against C. tropicalis R2 CIP203

Molecular probes and polymerase chain reaction (PCR) -based kits for diagnosis of shrimp diseases

Technology for effective and fast diagnosis of animal diseases is essential for developing aquaculture management strategies. This paper reviews the conventional techniques for shrimp disease diagnosis and discusses the emergence of nuclei acid probes and polymerase chain reaction (PCR)-based kits as powerful tools for rapid and accurate detection of shrimp diseases

Differential expression of akirin gene in black tiger shrimp Penaeus monodon in response to immunostimulant administration and infections with Vibrio harveyi and white spot syndrome virus

The akirin gene, which is strictly localized in the nucleus, plays a critical role in regulating antimicrobial peptide transcription, and has parallel functions to NF-kappa B signaling pathway in both vertebrates and invertebrates. In shrimp, the akirin gene is expressed as innate immunity in response to microbial infection. In the present study, expression of akirin gene in Penaeus monodon with respect to Vibrio harveyi and white spot syndrome virus (WSSV) infections and immunostimulant (beta-glucan) administration were investigated by quantitative polymerase chain reaction. The gene was expressed in various tissue samples of healthy shrimp. Maximum level of expression was immediately after V. harveyi infection, suggesting that it may be an early response gene. Gene expression was remarkably upregulated in the lymphoid organ, gill, and hepatopancreas, whereas downregulation was observed in hemocytes compared with the control. In the case of WSSV-infected samples, the akirin gene was significantly downregulated in the lymphoid organ but there was no significant difference in expression pattern in hemocytes compared to the control. In gill tissue, maximum expression was observed after 2 hr of infection, the same in hepatopancreas. Experimental challenge of beta-glucan fed shrimp infected with V. harveyi and WSSV resulted in significant upregulation of akirin gene expression in lymphoid and gill tissue

Future climate change conditions may compromise metabolic performance in juveniles of the mud crab Scylla serrata

This work was supported by a PhD scholarship granted by the University of Plymouth to EA (PI LMT).Research characterising the effects of future climate change on the marine environment remains heavily focussed on that of temperate regions and organisms. Furthermore, little is known of these effects on the early life stages of many marine species. Tropical regions are already experiencing an increase in sea surface temperature and decrease in sea surface salinity, conditions favoured by pathogenic bacteria such as Vibrio spp. The early life stages of crabs are known to be particularly vulnerable to both the direct physiological effects of climate change and exposure to harmful microorganisms, yet there are limited data on these effects on juveniles of many tropical crustacean species. This study assessed the metabolic responses of mud crab (Scylla serrata) juveniles to warming and/or freshening in the presence or absence of pathogenic bacteria in southwest India. Juvenile crabs were exposed to either ambient (28 °C/30 PSU) or one of three projected climate change regimes (28 °C/20 PSU (freshening), 32 °C/30 PSU (warming), 32 °C/20 PSU (warming + freshening)) for 10 days, in either the presence or absence of the pathogenic bacteria Vibrio parahaemolyticus. Results show that simulated climate change conditions, especially freshening, caused a significant increase in oxygen consumption rates (MO2), and that these were further increased when juveniles were exposed to V. parahaemolyticus. These results suggest that the effects of future climate change conditions could have significant implications for the conservation of wild stocks and commercial farming of this species in South Asia.Publisher PDFPeer reviewe