Diversity and function of microbial lipases within the mammalian gut

Background Current estimates suggest the majority of microbial proteins within the mammalian gut lack meaningful annotation. One such functional group are microbial lipases (EC:3.1.1.3), which can alter host access and utilisation of dietary fat. In this paper, we describe the diversity of lipolytic bacteria, including in vitro characterisation of a new lipase. Results Metagenomic sequence-based network analysis identified that the majority of microbial lipases in the gut of three host species (human, mouse, pig) belong to two unique clusters. These clusters were characterized by the presence of two novel motifs, AHSKGG and TTxxTPH, which may play a key functional role due to co-localisation in the active site, as identified by structural modelling. Analysis of metagenomic assembled genomes (MAGs) indicated that the majority of lipase-positive species belong to the phylum Firmicutes, although all dominant phyla within the human gut were represented by positive species. Metabolic analysis of these genomes identified a high prevalence of glycerol rather than fatty acid metabolism. The occurrence of microbial lipases determined across ~800 metagenomic gut samples depended on dietary fat consumption, with lipase expression increased in lard fed compared to palm oil fed mice. A representative lipase encoded within the genome of the species Clostridium symbiosum was cloned and its characterization confirmed the in silico prediction and provided detailed annotation to 373 proteins. Conclusions Microbial lipases within the gut represent a conserved group characterized by unique amino acid sequence motifs. While an increase in microbial lipase occurrence was positively associated with dietary fat intake, lipase-producing species seemed unable to metabolise the released fatty acids. In this paper, we provide a global analysis of the functional importance and diversity of microbial lipases within the intestine of mammals, which will improve the resolution of future sequence-based studies and open avenues for mechanistic experiments based on isolates. ### Competing Interest Statement The authors have declared no competing interest.