Phosphoethanolamine modification of lipid A found in five distinct Akkermansia species

Akkermansia is an important, diderm gut microbe associated with positive health outcomes. Recent advances in Akkermansia genomics have revealed great diversity in the genus, leading to the discovery of novel species and subspecies. Our knowledge of their individual interactions with the host is limited. One of the key questions concerning diderm commensals centers on their lipopolysaccharide and its outer membrane component, lipid A. Commensals must employ strategies that prevent eliciting lipid A-induced inflammation and resist cationic antimicrobial peptides, allowing them to colonize the host. In this study, lipid A was examined across representative isolates of five Akkermansia species to lay the foundation for investigating these host-microbe interactions across the genus. Lipid A of A. muciniphila, A. massiliensis , A. biwaensis , A. ignis , and A. durhamii ( N = 55) were analyzed by Matrix-Assisted Laser Desorption/Ionization mass spectrometry. All Akkermansia species produced lipid A modified with phosphoethanolamine (pEtN), which is associated with antimicrobial resistance and immune evasion. The relative abundance of modified lipid A varied among the species and positively correlated with decreased susceptibility to the antimicrobial peptide colistin. Intriguingly, the relative abundance of modified lipid A was independent of colistin presence. Instead, it increased as bacteria entered the stationary growth phase. Using proteomics approaches, cell envelope biogenesis-associated proteins were identified that could be involved in the associated outer membrane remodeling. To summarize, this study reports a novel lipid A modification and associated phenotypes in Akkermansia . Further work is warranted to determine its significance in the Akkermansia interactions with host cells in the gut.

IMPORTANCE

Akkermansia is a beneficial gut bacterium linked to metabolic and immune health. Yet we still know little about how different Akkermansia species interact with the human host. One key factor in these interactions is lipopolysaccharide (LPS), a molecule on the bacterial surface that can either stimulate or dampen inflammation. Here, we show that all investigated species share a chemical modification of LPS not previously reported in Akkermansia . This modification is associated with decreased sensitivity to antimicrobial peptide colistin and becomes more abundant as bacteria enter stationary phase, suggesting it is part of a regulated adaptation strategy rather than simply a response to antibiotic exposure. By identifying and functionally examining the modification, this work provides new insight into mechanisms that may support persistence in the intestinal environment.