R. bromii L2-63 annotation update. R. bromii L2-63 annotation update

Ruminococcus bromii is a dominant member of thehuman colonic microbiota that plays a ‘keystone’ rolein degrading dietary resistant starch. Recent evidencefrom one strain has uncovered a unique cellsurface ‘amylosome’ complex that organizes starchdegradingenzymes. New genome analysis presentedhere reveals further features of this complex andshows remarkable conservation of amylosome componentsbetween human colonic strains from threedifferent continents and a R. bromii strain from therumen of Australian cattle. These R. bromii strainsencode a narrow spectrum of carbohydrate activeenzymes (CAZymes) that reflect extreme specializationin starch utilization. Starch hydrolysis productsare taken up mainly as oligosaccharides, with onlyone strain able to grow on glucose. The humanstrains, but not the rumen strain, also possess transportersthat allow growth on galactose and fructose.R. bromii strains possess a full complement ofsporulation and spore germination genes and wedemonstrate the ability to form spores that surviveexposure to air. Spore formation is likely to be acritical factor in the ecology of this nutritionallyhighly specialized bacterium, which was previouslyregarded as ‘non-sporing’, helping to explain itswidespread occurrence in the gut microbiota throughthe ability to transmit between hosts.