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Mycobacterium smegmatis mc² 155 fbiC and MSMEG_2392 are involved in triphenylmethane dye decolorization and coenzyme F₄₂₀ biosynthesis

¹ Department of Biology, California State University-Fresno, Fresno, CA 937401, USA
² Irma Lerma Rangel College of Pharmacy, Texas A&M Health Science Center, Kingsville, TX 78363, USA

Correspondence
Mamta Rawat
mrawat{at}csufresno.edu

Mycobacteria can tolerate relatively high concentrations of triphenylmethane dyes such as malachite green and methyl violet. To identify mycobacterial genes involved in the decolorization of malachite green, a transposon mutant library of Mycobacterium smegmatis mc² 155 was screened for mutants unable to decolorize this dye. One of the genes identified was MSMEG_5126, an orthologue of Mycobacterium bovis fbiC encoding a 7,8-didemethyl-8-hydroxy-5-deazariboflavin (FO) synthase, which is essential for the biosynthesis of the electron carrier coenzyme F₄₂₀. The other gene identified was MSMEG_2392, encoding an alanine-rich protein with a DUF121 domain. The minimum inhibitory concentrations (MICs) for malachite green and methyl violet of the six fbiC mutants and two MSMEG_2392 mutants were one-third and one-fifth, respectively, of the MIC of the parent strain M. smegmatis mc² 155. Representative fbiC and MSMEG_2392 mutant strains were also sensitive to oxidative stress caused by the redox-cycling agents plumbagin and menadione, and the sensitivity was reversed in the complemented strains. HPLC analysis of representative fbiC and MSMEG_2392 strains revealed that, while the fbiC mutant lacked both coenzyme F₄₂₀ and FO, the MSMEG_2392 mutant contained FO but not coenzyme F₄₂₀. These results indicate that MSMEG_2392 is involved in the biosynthesis of coenzyme F₄₂₀.