Identification of a proton-chloride antiporter (EriC) by Himar1 transposon mutagenesis in Lactobacillus reuteri and its role in histamine production

Abstract

The gut microbiome may modulate intestinal immunity by luminal conversion of dietary amino acids to biologically active signals. The model probiotic organism Lactobacillus reuteri ATCC PTA 6475 is indigenous to the human microbiome, and converts the amino acid L-histidine to the biogenic amine, histamine. Histamine suppresses TNF production by human myeloid cells and is a product of L-histidine decarboxylation, which is a proton-facilitated reaction. A transposon mutagenesis strategy was developed based on a single-plasmid nisin-inducible Himar1 transposase/transposon delivery system for L. reuteri. A highly conserved proton-chloride antiporter gene (eriC), a gene widely present in the gut microbiome was discovered by Himar1 transposon (Tn)-mutagenesis presented in this study. Genetic inactivation of eriC by transposon insertion and genetic recombineering resulted in reduced ability of L. reuteri to inhibit TNF production by activated human myeloid cells, diminished histamine production by the bacteria and downregulated expression of histidine decarboxylase (hdc) cluster genes compared to those of WT 6475. EriC belongs to a large family of ion transporters that includes chloride channels and proton-chloride antiporters and may facilitate the availability of protons for the decarboxylation reaction, resulting in histamine production by L. reuteri. This report leverages the tools of bacterial genetics for probiotic gene discovery. The findings highlight the widely conserved nature of ion transporters in bacteria and how ion transporters are coupled with amino acid decarboxylation and contributed to microbiome-mediated immunomodulation.

Diacylglycerol kinase synthesized by commensal Lactobacillus reuteri diminishes protein kinase C phosphorylation and histamine-mediated signaling in the mammalian intestinal epithelium

“…Histamine is also a neurotransmitter that plays a key role in areas of the central nervous system enriched with histaminergic neurons such as the hippocampus 5 , 14 , 15 . Apart from mammals, microbes can synthesize histamine to maintain intracellular pH 16 , 17 . One such bacterium, Lactobacillus reuteri 6475 belongs to the phylum Firmicutes and is indigenous to the gastrointestinal tracts of avian and mammalian species 18 .…”

ClC transporter activity modulates histidine catabolism in Lactobacillus reuteri by altering intracellular pH and membrane potential

“…Despite lacking these other common acid resistance systems, our data suggest that the histidine decarboxylase system is not essential for the survival of L. reuteri under acid stress. However, histamine-generating capacity is known to be an important feature of L. reuteri’ s probiotic effect [12, 14, 17, 25].…”

“…A random mutagenesis screen located a potential HDC regulator in L. reuteri 6475. Knockout of a ClC proton/chloride antiporter EriC2 (previously annotated as EriC) significantly reduced histamine production and altered expression of the HDC gene cluster [25]. However, the exact role for EriC2 in histamine production has not been determined.…”

What Role Does the Endocannabinoid System Play in the Pathogenesis of Obesity?

“…Microbial changes affect the mechanisms of hunger and satiety, produce neuroactive substances and short-chain fatty acids (SCFA), and thus regulate nutritional behaviors associated with food consumption. Lactobacillus and Bifidobacterium strains are known to produce gamma-aminobutyric acid (GABA) [ 94 ], whereas L. reuteri produces histamine, and L. plantarum produces acetylcholine [ 95 ]. Furthermore, intestinal microorganisms can also moderate intestinal permeability and bile acid metabolism.…”