Charriere, G. | bioRxiv Science

bioRxiv2018

Microbial predator-prey interactions could favor coincidental selection of diverse virulence factors in marine coastal waters.

Vibrios are ubiquitous in marine environments and opportunistically colonize a broad range of hosts. Strains of Vibrio tasmaniensis present in oyster farms can thrive in oysters during juvenile mortality events. Among them, V. tasmaniensis LGP32 behaves as a facultative intracellular pathogen of oyster hemocytes, a property rather unusual in vibrios. Herein, we asked whether LGP32 resistance to phagocytosis could result from coincidental selection of virulence factors during interactions with heterotrophic protists, such as amoeba, in the environment. To answer that question, we developed an integrative study, from the first description of amoeba diversity in oyster-farming areas to the characterization of LGP32 interactions with amoebae of the Vannella genus that were found abundant in the oyster environment. LGP32 was shown to be resistant to grazing by amoebae and this phenotype was dependent on previously identified virulence factors: the secreted metalloprotease Vsm and the copper efflux p-ATPase CopA. Using dedicated in vitro assays, our results showed that these virulence factors act at different steps during amoeba-vibrio interactions than they do in oysters-vibrio interactions. Hence, the virulence factors of LGP32 are key determinants of biotic interactions with multiple hosts ranging from protozoans to metazoans, suggesting that the selective pressure exerted by amoebae in marine coastal environments favor coincidental selection of virulence factors.

microbiology↗

bioRxiv2018

Sympatric and allopatric evolutionary contexts shape differential immune response in Biomphalaria / Schistosoma interaction

Selective pressures between hosts and their parasites can result in reciprocal evolution or adaptation of specific life history traits. Local adaptation of resident hosts and parasites should lead to host-parasite systems performing better in sympatry when compared to allopatry. Between-population variations in parasite infectivity/virulence and host defence/resistance, referred to as compatibility phenotype, were often the proxy used to analyse sympatric or allopatric adaptation. Nevertheless, some reported cases exist where allopatric host-parasite systems demonstrate compatibility phenotypes similar or greater than the one observed in sympatry. In these cases, the role of local adaptation is worth considering. Here, we study the interaction between Schistosoma and its vector snail Biomphalaria in which such a discrepancy in local versus foreign compatibility phenotype has been observed. Herein, we developed an integrative approach to investigate sympatric and allopatric interaction processes and link the underlying molecular mechanisms to the resulting phenotypes. Using comparative \"omics\" approaches joined to analysis of life history traits (immune cellular response, mortality, prevalence and compatibility) we tried to bridge the gap of knowledge that exists for connecting local adaptation observations to molecular phenotypes in Schistosoma/Biomphalaria interactions.\n\nWe found that despite displaying similar prevalence phenotypes, parasite infection triggered an immune suppression in snails living in sympatry, while it activated an immune response for those living in allopatry. Dual-comparative molecular analyses revealed that parasite infection causes immune suppression in sympatry. miRNAs were used to hijack the hosts immune response, allowing sympatric parasites to initiate their developmental program earlier and more efficiently.\n\nWe show that despite having similar prevalence phenotypes, sympatric and allopatric snail-Schistosoma interactions displayed a strongly different immunobiological molecular dialogue. The ability of allopatric pathogens to adapt rapidly and efficiently to new hosts could have critical consequences on disease emergence and risk of schistosomiasis outbreaks. These observations would have important consequences in term of schistosomiasis disease control.

immunology↗