Jung, D.-J. | Search bioRxiv

bioRxiv2025

Bacterial glycosphingolipids orchestrate colonization and immune modulation in neonatal host

Symbiotic microbiota has co-existed with the mammalian host over millennia, conserving a stable community structure generation after generation. During the vertical transmission, gut symbionts rapidly colonize the unoccupied host lumen, nonetheless, how symbionts adapt to the dynamic changes of host environment, and contribute to the structural and immunological maturation remains elusive. Here, we show that the early gut symbiont Bacteroides fragilis produces a species- and stage-specific sphingolipid, alpha-galactosylceramide (BfaGC), that orchestrates neonatal colonization and immune modulation. BfaGC stabilizes membrane integrity and facilitates aerobic respiration, providing a critical advantage under early-life oxygen exposure. Temporally induced in the neonatal gut, BfaGC is necessary to regulate colonic type I natural killer T (NKT) cells, highlighting metabolic adaptation of the symbiont is synchronized with the time-sensitive host development. These findings reveal a mutualistic benefit exerted by endobiotic lipid metabolites in host-microbe interactions and provide new insights into species-specific mechanisms in early microbiota establishment and host immune education.

microbiology↗

bioRxiv2023

Functional and metagenomic level diversities of human gut symbiont-derived glycolipids

Bioactive metabolites produced by symbiotic microbiota causally impact host health and disease, nonetheless, incomplete functional annotation of genes as well as complexities and dynamic nature of microbiota make understanding species-level contribution in production and actions difficult. Alpha-galactosylceramides produced by Bacteroides fragilis (BfaGC) are one of the first modulators of colonic immune development, but biosynthetic pathways and the significance of the single species in the symbiont community still remained elusive. To address these questions at the microbiota level, we have investigated the lipidomic profiles of prominent gut symbionts and the metagenome-level landscape of responsible gene signatures in the human gut. We first elucidated the chemical diversity of sphingolipid biosynthesis pathways of major bacterial species. In addition to commonly shared ceramide backbone synthases showing two distinct intermediates, alpha-galactosyltransferase (agcT), the necessary and sufficient component for BfaGC production and host colonic type I natural killer T (NKT) cell regulation by B. fragilis, was characterized by forward-genetics based targeted metabolomic screenings. Phylogenetic analysis of agcT in human gut symbionts revealed that only a few ceramide producers have agcT and hence can produce aGCs, on the other hand, structurally conserved homologues of agcT are widely distributed among species lacking ceramides. Among them, alpha-glucosyl-diacylglycerol(aGlcDAG)-producing glycosyltransferases with conserved GT4-GT1 domains are one of the most prominent homologs in gut microbiota, represented by Enterococcus bgsB. Of interest, aGlcDAGs produced by bgsB can antagonize BfaGC-mediated activation of NKT cells, showing the opposite, lipid structure-specific actions to regulate host immune responses. Further metagenomic analysis of multiple human cohorts uncovered that the agcT gene signature is almost exclusively contributed by B. fragilis, regardless of age, geographical and health status, where the bgsB signature is contributed by >100 species, of which abundance of individual microbes is highly variable. Our results collectively showcase the diversities of gut microbiota producing biologically relevant metabolites in multiple layers-biosynthetic pathways, host immunomodulatory functions and microbiome-level landscapes in the host.

microbiology↗