Unexpected proteins involved in the regulation of secondary metabolism in <i>Myxococcus xanthus</i> DK1622

Regulating secondary metabolite (SM) in Myxococcus xanthus bears the potential to influence the formation of important natural products with various biological activities. The authors of this study have previously found that the detectable levels of two proteins (4-hydroxyphenylpyruvate dioxygenase [HppD] and a Hsp90-like protein [HtpG]) are affected by ROK inactivation. As evidence, the current study was designed to elucidate the possible role of these two proteins in regulating the SMs' biosynthesis in this bacterium. To begin with, inactivation of the corresponding genes was carried out, and two mutant strains (M. xanthus hppD^- and htpG^-) were constructed. Subsequently, high-performance liquid chromatography coupled with mass spectrometry analysis for the metabolic extracts of the mutants revealed a significant reduction in the production of several SMs, like DKxanthene, myxalamide A, and myxochromide A, in comparison to the wild type. Furthermore, electrophoretic mobility shift assays using purified ROK protein suggested a direct binding on the genes' promoter region encoding the two proteins under study. It is therefore possible to conclude that hppD and htpG genes are implicated in the bacterium SMs' biosynthetic regulatory cascade, which seems to be directly regulated by the ROK protein. The present study provides additional evidence to a previous investigation showing the pleiotropic regulatory role of ROK on the production of SMs in M. xanthus.