Vibriospecies cause infectious diseases in humans and animals, but they can also live as commensals within their host tissues. HowVibriosubverts the host defenses to mount a successful infection remains poorly understood, and this knowledge is critical for predicting and managing disease. Here, we have investigated the cellular and molecular mechanisms underpinning infection and colonization of 2 virulentVibriospecies in an ecologically relevant host model, oyster, to study interactions with marineVibriospecies. AllVibriostrains were recognized by the immune system, but only nonvirulent strains were controlled. We showed that virulent strains were cytotoxic to hemocytes, oyster immune cells. By analyzing host and bacterial transcriptional responses to infection, together withVibriogene knock-outs, we discovered thatVibrio crassostreaeandVibrio tasmaniensisuse distinct mechanisms to cause hemocyte lysis. WhereasV. crassostreaecytotoxicity is dependent on a direct contact with hemocytes and requires an ancestral gene encoding a protein of unknown function,r5.7,V. tasmaniensiscytotoxicity is dependent on phagocytosis and requires intracellular secretion of T6SS effectors. We conclude that proliferation of commensal vibrios is controlled by the host immune system, preventing systemic infections in oysters, whereas the successful infection of virulent strains relies onVibriospecies-specific molecular determinants that converge to compromise host immune cell function, allowing evasion of the host immune system.

To assess the impact of sanitation of a living environment on gut microbiota and development of the immune system, we raised BALB/c mice under three distinct environmental conditions: a specific pathogen-free animal room (SPF), a general animal room (XZ) and a farmhouse (JD). All other variables like diet, age, genetic background, physiological status and original gut microbiota were controlled for in the three groups. Using high-throughput sequencing of the 16S rRNA gene, we found that each mouse group had a specific structure of the gut microbial community. Groups JD and XZ harboured a significantly more diverse and richer gut microbiota than did group SPF. Bacteroidetes were significantly more abundant in groups XZ and JD than in group SPF, whereas Firmicutes showed the inverse pattern. Total serum immunoglobulin E (IgE) levels were significantly lower in groups XZ and JD than in group SPF. There were no significant differences in gut microbiota diversity and serum IgE concentration between groups JD and XZ, but we found higher abundance of dominant genera in the gut microflora of group JD. We conclude that exposure to soil, house dust and decaying plant material enhances gut microbial diversity and innate immunity. Our results seem to provide new evidence supporting the hygiene hypothesis.

As key players of gene regulation in many bacteria, small regulatory RNAs (sRNAs) associated with the RNA chaperone Hfq shape numerous phenotypic traits, including metabolism, stress response and adaptation, as well as virulence. sRNAs can alter target messenger RNA (mRNA) translation and stability via base pairing. sRNA synthesis is generally under tight transcriptional regulation, but other levels of regulation of sRNA signaling are less well understood. Here we used a fluorescence-based functional screen to identify regulators that can quench sRNA signaling of the iron-responsive sRNA RyhB in Escherichia coli. The identified regulators fell into two classes, general regulators (affecting signaling by many sRNAs) and RyhB-specific regulators; we focused on the specific ones here. General regulators include three Hfq-interacting sRNAs, CyaR, ChiX, and McaS, previously found to act through Hfq competition, RNase T, a 3′ to 5′ exonuclease not previously implicated in sRNA degradation, and YhbS, a putative GCN5-related N-acetyltransferase (GNAT). Two specific regulators were identified. AspX, a 3′end-derived small RNA, specifically represses RyhB signaling via an RNA sponging mechanism. YicC, a previously uncharacterized but widely conserved protein, triggers rapid RyhB degradation via collaboration with the exoribonuclease PNPase. These findings greatly expand our knowledge of regulation of bacterial sRNA signaling and suggest complex regulatory networks for controlling iron homeostasis in bacteria. The fluorescence-based genetic screen system described here is a powerful tool expected to accelerate the discovery of novel regulators of sRNA signaling in many bacteria.

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The Pacific oyster Crassostrea gigas is one of the main cultivated invertebrate species around the world. Since 2008, oyster juveniles have been confronted with a lethal syndrome, Pacific Oyster Mortality Syndrome (POMS). The etiology of POMS is complex. Recently, we demonstrated that POMS is a polymicrobial disease. It is initiated by a primary infection with the herpesvirus OsHV-1 μ Var, and evolves towards a secondary fatal bacteremia that is enabled by the oyster’s immunocompromised state. In the present article, we describe the implementation of an unprecedented combination of metabarcoding and metatranscriptomic approaches to show that the sequence of events in POMS pathogenesis is conserved across infectious environments and susceptible oyster genetic backgrounds. We also identify a core colonizing bacterial consortium which, together with OsHV-1 μ Var, forms the POMS pathobiota. This bacterial core is characterized by highly active global metabolism and key adaptive responses to the within-host environment (e.g. stress responses and redox homeostasis). Several marine gamma proteobacteria in the core express different and complementary functions to exploit the host’s resources. Such cross-benefits are observed in colonization-related functions, and reveal specific strategies used by these bacteria to adapt and colonize oysters (e.g. adhesion, cell defense, cell motility, metal homeostasis, natural competence, quorum sensing, transport, and virulence). Interdependence and cooperation within the microbial community for metabolic requirements is best exemplified by sulfur metabolism, which is a property of the pathobiota as a whole and not of a single genus. We argue that this interdependence may dictate the conservation of the POMS pathobiota across distinct environments and oyster genetic backgrounds.

Droplet-based microfluidic extraction is a promising way for effective lanthanides extraction due to its outstanding mass transfer performance. The separation process can be greatly enhanced with the droplet-based microfluidic extraction technique. However, the interactions between mass transfer, microfluidic dynamics and extraction kinetics are still unclear, which has hindered further manipulation on microfluidic extraction to boost extraction performance. In this study, the mechanisms of microfluidic droplet-based extraction and separation intensification of lanthanides are for the first time unveiled by using a numerical simulation model. The limiting factors for the performance of droplet-based microfluidic extraction are identified through a model-based parametric analysis. The numerical analyses provide a comprehensive understanding of droplet-based microfluidic extraction systems and offer operation and optimization guidelines for future research in this area.

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