Effects of vitamin B supply on cellular processes of the facultative vitamin B consumer .

Vitamin B (cobalamin, herein B) is a key cofactor for most organisms being involved in essential metabolic processes. In microbial communities, B is often scarce, largely because only few prokaryotes can synthesize B and are thus considered B-prototrophs. B-auxotrophy is mostly manifested by the absence of the B-independent methionine synthase, MetE. Here, we focus on bacteria that we classified as facultative B consumers as they encode both B-independent and -dependent (MetH) methionine synthases yet largely cannot synthesize B . The genus belongs to this group, and our work shows that upon B supply growth of is accelerated and autoinducer-2 (AI-2) concentrations are enhanced. We speculate that methionine synthesis efficiency, dependent on B availability, is linked to AI-2 synthesis. The precursor for AI-2 synthesis is S-adenosyl-L-homocysteine (SAH), which in turn requires methionine as a precursor. In almost all species studied, (B-binding protein), which is required for B uptake, and (Adenosylcobinamide-phosphate synthase), which enables remodeling of B-like compounds, are encoded on the same operon as (or , Adenosylhomocysteine nucleosidase), the first enzyme in the two-step AI-2 synthesis reaction. Transcriptomic analyses show that virulence factors, such as toxin synthesis, fimbriae formation, and activation of the type-6 secretion system, which have been shown to be regulated by quorum sensing via AI-2, are significantly upregulated in when B is available. Our results demonstrate that is a facultative B consumer and indicate that B availability affects AI-2 levels and thus potentially virulence factor regulation.IMPORTANCEMetabolites play a key role in microbial metabolism and communication. While vitamin B is an essential cofactor for important enzymatic reactions, autoinducer-2 mediates interspecies signaling and can regulate the expression of genes that are crucial for virulence and survival. In our study, we hypothesize and present findings how these two important metabolites are linked in species. grows without B but at an accelerated rate when B is present, and we detect higher AI-2 values in cultures with B amendment. Transcriptome analyses show how vitamin B availability significantly upregulates gene expression of virulence factors such as toxin synthesis, fimbrial formation, and activation of the type-6 secretion system in .