Ruminococcus gnavus was isolated from human faecal samples of a healthy adult human individual. This study aims to investigate mucin degradation by focussing on the utilisation of terminal mucin glycans.. Ruminococcus gnavus genome sequence

We previously identified and characterised an intramolecular trans-sialidase (IT-sialidase) in the gut symbiont Ruminococcus gnavus ATCC 29149, which is associated to the ability of the strain to grow on mucins. In this work we have obtained and analysed the draft genome sequence of another mucin-degrader R. gnavus strain ATCC 35913 isolated from a healthy individual. Transcriptomics analyses of both ATCC 29149 and ATCC 35913 strains confirmed that the strategy utilised by R. gnavus for mucin-degradation is focused on utilisation of terminal mucin glycans. R. gnavus ATCC 35913 also encodes a predicted IT-sialidase and harbours a Nan cluster dedicated to sialic acid utilisation. We showed that the Nan cluster was upregulated when the strains were grown in presence of mucin and 3’sialyl-lactose. In addition we demonstrated that both R. gnavus strains were able to grow on 2,7-anyhydro-Neu5Ac, the IT-sialidase transglycosylation product, as a sole carbon source. Taken together these data further support the hypothesis that IT-sialidase expressing gut microbes, provide commensal bacteria such as R. gnavus with a nutritional competitive advantage, by accessing and transforming a source of nutrient to their own benefit.