Bacterial taxa decoupling with ageing

reflected in the gut microbiota, in such a way that taxa and associated functions differ between younger an older people [1]. Moreover, we have compelling evidence that some gut bacterial functions are increasingly decoupled with age, contradicting the general assumption that the gut microbiota as a whole systematically contributes to our health status as we age. By performing shotgun and target proteomics and target metabolomics studies, Ruiz et al. [2] have identified a reproducible microbiome profile that differed among age groups (i.e., infants, adults and elderly) but, more importantly, they detected metabolic deficits in our gut bacteria as we get older [2]. The shotgun proteomes revealed that the number of proteins produced by our gut bacteria increases with age and that many of them differ from those harbored when younger. By using target proteomics these differences were found to be statistically significant in two of the 437 proteinfunctions identified, namely KO1667 (TnaA, tryptophanase) and KO1696 (TrpB, tryptophan synthase), given that their expression values were high in infants, intermediate in adults and practically null in the elderly. TrpB is essential for tryptophan synthesis and TnaA is essential for converting tryptophan into indole. The progressive decline in the intestinal microbiota from childhood to old age of these two essential products, tryptophan and indole, were validated by measuring their relative concentration in the fecal fluid using a target metabolomics approach, observing a spectacular drop in both of them with age. Half-life analyses showed that these molecules are reduced to 50% between 11-31 years with an even greater reduction of 90% between 34-54 years of age. In a previous study by our group [3] we also detected a low presence of tnaA and trpB genes in the gut microbiota of the adult population. We therefore speculate, from an evolutionary perspective, that those genes and the corresponding bacterial taxa could be maximized in the reproductive period of the human species.