naphthoquinones and malachite-green

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.

Topics: Anti-Bacterial Agents; Coloring Agents; DNA Transposable Elements; Gene Deletion; Genetic Complementation Test; Gentian Violet; Microbial Sensitivity Tests; Mutagenesis, Insertional; Mycobacterium smegmatis; Naphthoquinones; Riboflavin; Riboflavin Synthase; Rosaniline Dyes; Vitamin K 3