A mucin-regulated adhesin determines the spatial organization and inflammatory character of a bacterial symbiont in the vertebrate gut

In a healthy gut, microbes are often aggregated with host mucus, yet the molecular basis for this organization and its impact on intestinal health are unclear. Mucus is a viscous physical barrier separating resident microbes from epithelia, but also provides glycan cues that regulate microbial behaviors. Here, we describe a mucin-sensing pathway in an Aeromonas symbiont of zebrafish, Aer01. In response to the mucin-associated glycan N-acetylglucosamine, a sensor kinase regulates expression of an aggregation-promoting adhesin we named MbpA. Upon MbpA disruption, Aer01 colonizes to normal levels, but is largely planktonic and more immunogenic. Increasing cell surface MbpA rescues these traits. MbpA-like adhesins are common in human-associated bacteria and expression of an Akkermansia muciniphila MbpA-like adhesin in MbpA-deficient Aer01 restores lumenal aggregation and reverses its pro-inflammatory character. Our work demonstrates how resident bacteria use mucin glycans to modulate behaviors congruent with host health. The larval zebrafish symbiont, Aeromonas ZOR0001 (Aer01), forms denser aggregates in the mucin-rich gut lumen of its host or when exposed to the mucin-associated sugar N-acetylglucosamine (GlcNAc). To investigate the genetic basis of this response in culture we exposed Aer01 to 0.4% GlcNAc or 0.4% Glucose, a glycan that doesn’t promote Aer01 aggregation. We similarly exposed two experimentally evolved Aer01 isolates that fail to aggregate when exposed to GlcNAc to this sugar to determine how Aer01 GlcNAc-mediated transcriptional responses are altered in these isolates. RNA was harvested after 6 hours of GlcNAc or Glucose exposure and submitted to SeqCenter for RNA-seq analysis.