Journal
MICROBIOLOGY-SGM
Volume 153, Issue -, Pages 1546-1555Publisher
MICROBIOLOGY SOC
DOI: 10.1099/mic.0.2006/004234-0
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The genes nepAB of a small multidrug resistance (SMR) pump were identified as part of the pAO1-encoded nicotine regulon responsible for nicotine catabolism in Arthrobacter nicotinovorans. When [C-14]nicotine was added to the growth medium the bacteria exported the C-14-labelled end product of nicotine catabolism, methylamine. In the presence of the proton-motive force inhibitors 2,4-dinitrophenol (DNP), carbonyl cyanide m-chlorophenylhydrazone (CCCP) or the proton ionophore nigericin, export of methylannine was inhibited and radioactivity accumulated inside the bacteria. Eff lux of [C-14]nicotine-derived radioactivity from bacteria was also inhibited in a pmfR: cmx strain with downregulated nepAB expression. Because of low annine oxidase levels in the pmfR: cmx strain, gamma-N-methylaminobutyrate, the methylamine precursor, accumulated. Complementation of this strain with the nepAB genes, carried on a plasmid, restored the efflux of nicotine breakdown products. Both NepAand NepBwere required forfull export activity, indicating thattheyform atwocomponent efflux pump. NepAB may function as a metabolic valve by exporting methylamine, the end product of nicotine catabolism, and, in conditions under which it accumulates, the intermediate gamma-N-methylaminobutyrate.
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