Alginate microgels encapsulation strategy of silver nanoparticles active against Candida albicans

Nanoparticles (NPs), offering high specific surface, are considered as the best potential anti-microbial agents for a wide range of medical nanotechnology. Among them, silver NPs (AgNPs) allow high biocidal activity. A design of ecological capsules is proposed where AgNPs of 22 nm in diameter are grafted on the surface of biobased nanocrystals obtained from cellulose (CNC) and chitin (ChiNC). These silver nanohybrids are dispersed in calcium-alginate microgels of 45–50 µm in diameter using microfluidic tools. Such double level of immobilization of AgNPs leads to highly stable carriers, prolongs shelf life and raises bioactivity, with a precise control of well dispersed AgNPs as determined by scanning transmission electron microscopy, UV-Vis spectroscopy and atomic absorption spectroscopy. Preliminary tests for antimicrobial activities of these new microgels have shown a significant inhibitory effect on Candida albicans, the most common fungal pathogen, responsible for thrush and vaginal yeast infections, for very low levels of silver

Mining of the biosynthetic mechanisms of Vibrio spp. polysaccharides and potential role in biofilm formation

Vibrio spp. are ubiquitous marine bacteria that are ecologically and metabolically diverse members of planktonic and animal associated microbial communities. They encompass the ancient and well-studied human pathogen, Vibrio cholerae, and two other human pathogens, V. vulnificus and V. parahaemolyticus, as well as some less thoroughly characterized animal pathogens. Virulence is based on a wide diversity of mechanisms involved in motility and host colonization, in ability to persist and develop, and in damage generation. Polysaccharides may play major roles in virulence and are major components of extracellular polymeric matrix synthesized upon biofilm growth. They may also exhibit biological features, especially those similar to animal-derived glycosaminoglycans (GAG). Bacterial polysaccharides include EPSs which are released to the surrounding medium, and two surface polysaccharides: lipopolysaccharides (LPS) with an O-antigen polysaccharide linked to the Lipid A core complex and capsular polysaccharides (CPS) with K-antigen. Diversity of biosynthetic pathways involved in glycopolymers biosynthesis in Vibrio spp. was analysed through in silico identification of genes encoding CAZYmes and comparative genomic approaches. In parallel, ability to form biofilm and extracellular matrix composition is studied. The aim is to provide a better knowledge of the polysaccharide gene cluster importance and to facilitate discovery of new bioactive carbohydrate compounds

Characterization of biofilm extracts from two marine bacteria

In the marine environment, biofilm formation is an important lifestyle for microorganisms. A biofilm is comprised of cells embedded in an extracellular matrix that holds them close together and keeps the biofilm attached to the colonized surface. This predominant lifestyle and its main regulation pathway, namely quorum-sensing (QS), have been shown to induce specific bioactive metabolites. In this study, we investigated the biofilm formation by two marine bacteria belonging to the Vibrio species to discover potentially innovative bioactive compounds. We proposed a protocol to isolate biofilm extracts, to analyze their biochemical composition, and to compare them to planktonic cell extracts. Cells were grown attached to a plastic surface; extracts were prepared in water, NaOH, or in ethyl acetate and analyzed. Extracellular matrix components featured carbohydrates, proteins, lipids, and low amount of DNA. Carbohydrates appeared to be the main constituent of biofilm but also of the planktonic cell supernatant. Moreover, antimicrobial and QS-signaling activities were evidenced in extracts

Impact of Putative Probiotics on Growth, Behavior, and the Gut Microbiome of Farmed Arctic Char (Salvelinus alpinus)

Beneficial bacteria promise to promote the health and productivity of farmed fish species. However, the impact on host physiology is largely strain-dependent, and studies on Arctic char (Salvelinus alpinus), a commercially farmed salmonid species, are lacking. In this study, 10 candidate probiotic strains were subjected to in vitro assays, small-scale growth trials, and behavioral analysis with juvenile Arctic char to examine the impact of probiotic supplementation on fish growth, behavior and the gut microbiome. Most strains showed high tolerance to gastric juice and fish bile acid, as well as high auto-aggregation activity, which are important probiotic characteristics. However, they neither markedly altered the core gut microbiome, which was dominated by three bacterial species, nor detectably colonized the gut environment after the 4-week probiotic treatment. Despite a lack of long-term colonization, the presence of the bacterial strains showed either beneficial or detrimental effects on the host through growth rate enhancement or reduction, as well as changes in fish motility under confinement. This study offers insights into the effect of bacterial strains on a salmonid host and highlights three strains, Carnobacterium divergens V41, Pediococcus acidilactici ASG16, and Lactiplantibacillus plantarum ISCAR-07436, for future research into growth promotion of salmonid fish through probiotic supplementation

The gut microbiome of farmed Arctic char (Salvelinus alpinus) is shaped by feeding stage and nutrient presence

The gut microbiome plays an important role in maintaining health and productivity of farmed fish. However, the functional role of most gut microorganisms remains unknown. Identifying the stable members of the gut microbiota and understanding their functional roles could aid in the selection of positive traits or act as a proxy for fish health in aquaculture. Here, we analyse the gut microbial community of farmed juvenile Arctic char (Salvelinus alpinus) and reconstruct the metabolic potential of its main symbionts. The gut microbiota of Arctic char undergoes a succession in community composition during the first weeks post hatch, with a decrease in Shannon diversity and the establishment of three dominant bacterial taxa. The genome of the most abundant bacterium, a Mycoplasma sp., shows adaptation to rapid growth in the nutrient rich gut environment. The second most abundant taxon, a Brevinema sp., has versatile metabolic potential, including genes involved in host mucin degradation and utilisation. However, during periods of absent gut content, a Ruminococcaceae bacterium becomes dominant, possibly outgrowing all other bacteria through the production of secondary metabolites involved in quorum sensing and cross-inhibition while benefiting the host through short-chain fatty acid production. Whereas Mycoplasma is often present as a symbiont in farmed salmonids, we show that the Ruminococcaceae species is also detected in wild Arctic char, suggesting a close evolutionary relationship between the host and this symbiotic bacterium

Screening of marine lactic acid bacteria for Vibrio parahaemolyticus inhibition and application to depuration in Pacific oysters (Crassostrea gigas)

Aims This study aims to assess the use of marine lactic acid bacteria (LAB) to reduce V. parahaemolyticus levels during oyster depuration process. Methods and Results The inhibitory effect of thirty marine LAB strains against V. parahaemolyticus strains was evaluated by in vitro assays. Three positive strains (Latilactobacillus sakei SF1583, Lactococcus lactis SF1945 and Vagococcus fluvialis CD264) were selected for V. parahaemolyticus levels reduction during oyster depuration. Pacific oysters Crassostrea gigas were artificially and independently contaminated by four GFP-labelled V. parahaemolyticus strains (IFVp201, IFVp69, IFVp195 and LMG2850T) at 105 CFU.mL−1 and then exposed by balneation to 106 CFU.mL−1 of each LAB strains during 24 h, at 19°C. Quantification of V. parahaemolyticus in haemolymph by flow cytometry revealed variations in natural depuration of the different V. parahaemolyticus strains alone. Furthermore, the addition of LABs improved up to 1-log bacteria.mL−1 the reduction of IFVp201 concentration in comparison to the control condition. Conclusions Although further optimizations of procedure are needed, addition of marine LABs during oyster depuration may be an interesting strategy to reduce V. parahaemolyticus levels in C. gigas. Significance and impact of the study Our study provides promising ways to develop a depuration process which could potentially be implemented in oyster farms

Screening of marine lactic acid bacteria for Vibrio parahaemolyticus inhibition and application to depuration in Pacific oysters (Crassostrea gigas)

International audienceAims This study aims to assess the use of marine lactic acid bacteria (LAB) to reduce Vibrio parahaemolyticus levels during oyster depuration process. Methods and results The inhibitory effect of 30 marine LAB strains against V. parahaemolyticus strains was evaluated by in vitro assays. A total of three positive strains (Latilactobacillus sakei SF1583, Lactococcus lactis SF1945, and Vagococcus fluvialis CD264) were selected for V. parahaemolyticus levels reduction during oyster depuration. Pacific oysters Crassostrea gigas were artificially and independently contaminated by four GFP-labelled V. parahaemolyticus strains (IFVp201, IFVp69, IFVp195, and LMG2850 T) at 10 5 CFU ml −1 and then exposed by balneation to 10 6 CFU ml −1 of each LAB strains during 24 h, at 19 • C. Quantification of V. parahaemolyticus in haemolymph by flow cytometry revealed variations in natural depuration of the different V. parahaemolyticus strains alone. Furthermore, the addition of LABs improved up to 1-log bacteria ml −1 the reduction of IFVp201 concentration in comparison to the control condition. Conclusions Although further optimizations of procedure are needed, addition of marine LABs during oyster depuration may be an interesting strategy to reduce V. parahaemolyticus levels in Crassostrea gigas. Significance and impact of the study Our study provides promising ways to develop a depuration process, which could potentially be implemented in oyster farms

New Insight into Antimicrobial Compounds from Food and Marine-Sourced Carnobacterium Species through Phenotype and Genome Analyses

Carnobacterium maltaromaticum and Carnobacterium divergens, isolated from food products, are lactic acid bacteria known to produce active and efficient bacteriocins. Other species, particularly those originating from marine sources, are less studied. The aim of the study is to select promising strains with antimicrobial potential by combining genomic and phenotypic approaches on large datasets comprising 12 Carnobacterium species. The biosynthetic gene cluster (BGCs) diversity of 39 publicly available Carnobacterium spp. genomes revealed 67 BGCs, distributed according to the species and ecological niches. From zero to six BGCs were predicted per strain and classified into four classes: terpene, NRPS (non-ribosomal peptide synthetase), NRPS-PKS (hybrid non-ribosomal peptide synthetase-polyketide synthase), RiPP (ribosomally synthesized and post-translationally modified peptide). In parallel, the antimicrobial activity of 260 strains from seafood products was evaluated. Among the 60% of active strains, three genomes were sequenced and submitted to a dereplication process. C. inhibens MIP2551 produced a high amountof H2O2, probably thanks to the presence of four oxidase-encoding genes. C. maltaromaticum EBP3019 and SF668 strains were highly efficient against Listeria monocytogenes. A new extracellular 16 kDa unmodified bacteriocin in the EBP3019 strain and five different bacteriocins in SF668 were highlighted. In this study, the overview of antimicrobial BGC and inhibitory activities of Carnobacterium spp. allowed the prediction of potential innovative natural products that could be relevant for biotechnological application