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EriC2 Regulates Histamine Production Machinery via an Ion Transport‐Dependent Mechanism in Lactobacillus reuteri
Author(s) -
Hall Anne,
Engevik Melinda,
Versalovic James
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.744.6
Subject(s) - lactobacillus reuteri , antiporter , histamine , intracellular , chemistry , intracellular ph , ion transporter , biochemistry , microbiology and biotechnology , biophysics , membrane potential , biology , lactobacillus , membrane , pharmacology , fermentation
Background Certain strains of Lactobacillus reuteri can reduce inflammation and tissue damage in mouse models of colitis. This anti‐inflammatory capacity stems in part from L. reuteri’ s ability to produce and secrete histamine, which can act on specific receptors present on mammalian cells. In the bacteria, histamine is generated by histidine decarboxylase (HdcA), and released from the cell by a histidine/histamine exchanger (HdcP). This process consumes protons, resulting in an increasingly alkaline intracellular pH and an inside‐negative membrane potential. These factors can suppress the activities of HdcA and HdcP. However, hdcA is not constitutively expressed, and it is unclear which signals may trigger its upregulation. Additionally, it is unknown how L. reuteri balances its internal ion environment during histamine production, especially in the presence of a complex external environment like the GI tract. A proton/chloride antiporter, EriC2, was recently identified in L. reuteri as a potential regulator of intracellular pH and membrane potential, and thus histamine production. We hypothesize that EriC2 maintains intracellular pH via proton influx and membrane potential via chloride efflux at levels that allow histamine production by L. reuteri . Methods & Results To investigate how EriC2 ion transport might alter expression and function of histamine production machinery in L. reuteri , single‐strand recombineering was used to generate protein knockout, proton transport deficient, and transport null EriC2 strains. These mutations are stable, and do not significantly alter the growth of the resulting strains compared to wild‐type (WT) L. reuteri . Intracellular pH was assessed in each strain with the pH‐sensitive fluorophore, pHrodo Green AM. Loss of ion transport via EriC2 increases intracellular pH, supporting its potential role in maintaining the intracellular proton pool. RT‐qPCR showed that hdcA gene expression is increased in EriC2 transport mutants relative to the WT strain. T84 secretory colonic epithelial cells were co‐cultured with WT and EriC2 mutant L. reuteri strains. Host gene expression was examined via RT‐qPCR, and differential expression of histamine receptors was observed in the presence of mutant L. reuteri strains. Conclusion Together these data suggest that EriC2 ion transport mutants differentially regulate histamine production machinery in L. reuteri, and can lead to changes in host physiology. The beneficial effects of L. reuteri‐ derived histamine may depend on a regulatory system mediated by ion transport in the GI tract. A mechanistic understanding of histamine production by the gut microbiome may enable the development of diet or probiotic‐based strategies to suppress intestinal inflammation.