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. Overall design: 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.