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A Bacillus subtilis Δ pdxT mutant suppresses vitamin B6 limitation by acquiring mutations enhancing pdxS gene dosage and ammonium assimilation
Author(s) -
Richts Björn,
Lentes Sabine,
Poehlein Anja,
Daniel Rolf,
Commichau Fabian M.
Publication year - 2021
Publication title -
environmental microbiology reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.229
H-Index - 69
ISSN - 1758-2229
DOI - 10.1111/1758-2229.12936
Subject(s) - bacillus subtilis , mutant , gene , biology , microbiology and biotechnology , chemistry , bacteria , genetics
Summary Pyridoxal‐5′‐phosphate (PLP), the biologically active form of vitamin B6, serves as a cofactor for many enzymes. The Gram‐positive model bacterium Bacillus subtilis synthesizes PLP via the PdxST enzyme complex, consisting of the PdxT glutaminase and the PdxS PLP synthase subunits, respectively. PdxT converts glutamine to glutamate and ammonia of which the latter is channelled to PdxS. At high extracellular ammonium concentrations, the PdxS PLP synthase subunit does not depend on PdxT. Here, we assessed the potential of a B. subtilis Δ pdxT mutant to adapt to PLP limitation at the genome level. The majority of Δ pdxT suppressors had amplified a genomic region containing the pdxS gene. We also identified mutants having acquired as yet undescribed mutations in ammonium assimilation genes, indicating that the overproduction of PdxS and the NrgA ammonium transporter partially relieve vitamin B6 limitation in a Δ pdxT mutant when extracellular ammonium is scarce. Furthermore, we found that PdxS positively affects complex colony formation in B. subtilis . The catalytic mechanism of the PdxS PLP synthase subunit could be the reason for the limited evolution of the enzyme and why we could not identify a PdxS variant producing PLP independently of PdxT at low ammonium concentrations.