Products of gut microbial Toll/interleukin-1 domain NADase activities in gnotobiotic mice and healthy and malnourished Bangladeshi children

Recent work indicates that Toll/Interleukin-1 receptor (TIR) domain-containing proteins can hydrolyze NAD. Given increasing attention to how the gut microbiome contributes to NAD metabolism and healthy growth, we examined the representation and expressed NAD hydrolase (NADase) activities of its TIR domains. The NADase activities of 152 bacterial TIRs were characterized in vitro. Gut bacterial strains representing the diversity of TIRs observed in the microbiome, and activities observed in vitro, were introduced into germ-free mice fed defined diets. Mass spectrometry of cecal metabolites disclosed that a product of TIR NADase activity, variant cyclic-ADPR-x (v-cADPR-x), distinguished colonized from germ-free animals. Mass spectrometry and microbial RNA-Seq of gnotobiotic mice colonized with one, two and all members of this bacterial consortium, identified Bacteroides xylanisolvens as the principal in vivo source of v-cADPR-x. Guided by bioinformatic analyses of biochemically validated TIR domains, we determined that compared to age-matched healthy Bangladeshi children, those with acute malnutrition had significantly lower fecal levels of TIRs known or predicted to generate v-cADPR-x, and of this metabolite. These results indicate that v-cADPR-x may be an informative biomarker of healthy gut microbiome development.