Resident gut microbes co-exist with transient bacteria to form the gut microbiota. Despite increasing evidence suggesting a role for transient microbes on gut microbiota function, the interplay between resident and transient members of this microbial community is poorly defined. We aimed to determine the extent to which a host's autochthonous gut microbiota influences niche permissivity to transient bacteria using a fermented milk product (FMP) as a vehicle for five food-borne bacterial strains. Using conventional and gnotobiotic rats and gut microbiome analyses (16S rRNA genes pyrosequencing and reverse transcription qPCR), we demonstrated that the clearance kinetics of one FMP bacterium, Lactococcus lactis CNCM I-1631, were dependent on the structure of the resident gut microbiota. Susceptibility of the resident gut microbiota to modulation by FMP intervention correlated with increased persistence of L. lactis. We also observed gut microbiome configurations that were associated with altered stability upon exposure to transient bacteria. Our study supports the concept that allochthonous bacteria have transient and subject-specific effects on the gut microbiome that can be leveraged to re-engineer the gut microbiome and improve dysbiosis-related diseases.

Beneficial microbes that target molecules and pathways, such as oxidative stress, which can negatively affect both host and microbiota, may hold promise as an inflammatory bowel disease therapy. Prior work showed that a five-strain fermented milk product (FMP) improved colitis in T-bet−/−Rag2−/− mice. By varying the number of strains used in the FMP, we found that Lactococcus lactis I-1631 was sufficient to ameliorate colitis. Using comparative genomic analyses, we identified genes unique to L. lactis I-1631 involved in oxygen respiration. Respiration of oxygen results in reactive oxygen species (ROS) generation. Also, ROS are produced at high levels during intestinal inflammation and cause tissue damage. L. lactis I-1631 possesses genes encoding enzymes that detoxify ROS, such as superoxide dismutase (SodA). Thus, we hypothesized that lactococcal SodA played a role in attenuating colitis. Inactivation of the sodA gene abolished L. lactis I-1631’s beneficial effect in the T-bet−/−Rag2−/− model. Similar effects were obtained in two additional colonic inflammation models, Il10−/− mice and dextran sulfate sodium-treated mice. Efforts to understand how a lipophobic superoxide anion (O2−) can be detoxified by cytoplasmic lactoccocal SodA led to the finding that host antimicrobial-mediated lysis is a prerequisite for SodA release and SodA’s extracytoplasmic O2− scavenging. L. lactis I-1631 may represent a promising vehicle to deliver antioxidant, colitis-attenuating SodA to the inflamed intestinal mucosa, and host antimicrobials may play a critical role in mediating SodA’s bioaccessibility.

Sessile marine species such as Anthozoans act as ecosystem engineers due to their three-dimensional structure. Gorgonians, in particular, can form dense underwater forests that give shelter to other species increasing local biodiversity. In the last decades, several Mediterranean gorgonians populations have been affected by natural and anthropogenic impacts which drastically reduced their size. However, some species showed unexpected resilience, mainly due to the supply of new individuals. To understand the mechanisms underlying recovery processes, studies on the first life history stages (i.e. larval dispersal, settlement and recruitment) are needed. In tropical coral reefs, crustose coralline algae (CCA) are known to influence coral larvae habitat selection and settlement. This capacity however is not ubiquitous among CCA species and larvae of different coral species may have different preferences. The present work focuses on three Mediterranean gorgonians (Eunicella singularis, Paramuricea clavata and Corallium rubrum) with the objective of quantifying settlement and recruitment in presence of two common CCA species (Litophyllum styctaeforme and Litophyllum incrustans). Results showed that the presence of CCA activates earlier settlement in E. singularis and increase the density of recruits, with different trends for the three species. Our results suggest that CCA should be taken into account in the implementation of conservation strategies. Moreover, a deeper comprehension of settlement mechanisms could help improving restoration techniques based on sexual reproduction.

International audienceDistribution and abundance of coral diseaseshave been well documented, but only a few studies con-sidered diseases affecting crustose coralline algae (CCA),particularly at the species level. We investigated the spa-tiotemporal dynamics of diseases affecting CCA along thesouth coast of Curac¸ao, southern Caribbean. Two syn-dromes were detected: the Coralline White Band Syndrome(CWBS) previously described and the Coralline WhitePatch Disease (CWPD) reported here for the first time.Diseases were present at all six study sites, and our resultsdid not reveal a relationship between disease occurrenceand human influence. Both diseases were more prevalenton the shallower reef flat than on the deeper reef slope, andduring the warm/rainy season than during the cold/dryseason. The patterns observed were consistent with apositive link between temperature and disease occurrence.Reef flat communities were dominated by Neogoniolithonmamillare and Paragoniolithon solubile, whereas deeperhabitats were dominated by Hydrolithon boergesenii. Dis-eases affected all the species encountered, and no prefer-able host was detected. There was a significant relationshipbetween both disease occurrences and CCA cover. Moni-toring of affected patches revealed that 90 % of lesions inCWBS increased in size, whereas 88 % of CWPD lesionsregenerated over time. CWBS linear progression rate didnot vary between seasons or species and ranged from 0.15to 0.36 cm month -1 , which is in the same order of mag-nitude as rates previously documented. We conclude thatdiseases have the potential to cause major loss in CCAcover, particularly in shallow waters. As CCA play a keyrole in reef ecosystems, our study suggests that the emer-gence of diseases affecting these algae may pose a realthreat to coral reef ecosystems. The levels of diseasereported here will provide a much-needed local baselineallowing future comparisons