Coordinate regulation of virulence and metabolic genes by the transcription factor HbhR in Mycobacterium marinum

Abstract

The heparin-binding hemagglutinin (HBHA) is a multifunctional protein involved in adherence ofMycobacterium tuberculosis to non-phagocytic cells and in the formation of intracytosolic lipid inclusions. We demonstrate that the expression of hbhA is regulated by a transcriptional repressor, named HbhR, in Mycobacterium marinum. The hbhR gene, located upstream of hbhA, was identified by screening a transposon insertion library and detailed analysis of a mutant overproducing HBHA. HbhR was found to repress both hbhA and hbhR transcription by binding to the promoter regions of both genes. Complementation restored production of HBHA. RNA-seq analyses comparing the mutant and parental strains uncovered 27 genes, including hbhA, that were repressed and 20 genes activated by HbhR. Among the former, the entire locus of genes coding for a type-VII secretion system, including esxA, esxB and pe-ppe paralogs, as well as the gene coding for PspA, present in intracellular lipid vesicles, was identified, as was katG, a gene involved in the sensitivity to isoniazid. The latter category contains genes that play a role in diverse functions, such as metabolism and resistance to oxidative conditions. Thus, HbhR appears to be a master regulator, linking the transcriptional regulation of virulence, metabolic and antibiotic sensitivity genes in M. marinum. . Transcriptional regulation involved in virulence and metabolism of M. marinum 53

MLDSR, the transcriptional regulator of the major lipid droplets protein MLDS, is controlled by long‐chain fatty acids and contributes to the lipid‐accumulating phenotype in oleaginous Rhodococcus strains

“…Our transcriptomic data indicated that MLDSR positively or negatively regulates several genes participating in diverse cellular functions, including lipid metabolism, redox metabolism, central metabolism, cellular stress, transport, or DNA processing, which probably contribute to the adaptation of the microorganism to fluctuating environmental conditions. A previous study demonstrated the role of the MLDSR ortholog, HbhR, as a master regulator linking the transcriptional regulation of virulence, metabolism, and antibiotic sensitivity genes in M. marinum [21]. However, we did not find a high correlation between the genes under the control of the respective regulatory proteins (MLDSR and HbhR) comparing transcriptomic data of R. jostii and M. marinum.…”

“…Some of them are probably involved in TAG degradation and β‐oxidation of fatty acids (Table 2). A similar analysis was repeated by using the imperfect inverted repeat CTTGCAA(A/T)AGCAAG reported for Rv0474 [20] and HbhR [21], both homologs proteins of MLDSR in Mycobacterium tuberculosis and Mycobacterium marinum , respectively. Again, the best score corresponded to the binding site located upstream of the mldsr‐mlds cluster, and the occurrence of putative binding sequences was also present in upstream regions of some genes associated with lipid catabolism (Table S4).…”

“…The peculiar mldsr‐mlds gene arrangement and the presence of two DNA binding boxes for MLDSR upstream of this gene cluster suggest a unique regulation mechanism in oleaginous rhodococcal strains that differentiates them from nonoleaginous rhodococci and mycobacteria, in which the occurrence of MLDSR orthologs (Rv0474 and HbhR) have been reported [20,21]. Rv0474 and HbhR have been described as repressors of HBHA (ortholog of MLDS), and the respective binding boxes are found as discrete and unique motif in the upstream region of both hbhR and hbhA genes [21]. In contrast, the mldsr‐mlds gene pair is tightly co‐regulated in rhodococci.…”

“…The difference in gene arrangements in rhodococci and mycobacteria, as well as the occurrence of two putative boxes in oleaginous rhodococci, may be linked to a dual role of MLDSR as activator and repressor in oleaginous rhodococci and could explain the different phenotypes observed for the respective mldsr mutants, to some extent. In this context, the mutation of tadR / mldsr genes in R. opacus PD630 and R. jostii RHA1, respectively, promoted a decrease in TAG content, whereas the mutation of hbhR resulted in an increase of TAG content in M. marinum [21].…”

“…Table S4. MLDSR putative binding sites upstream of associated genes to lipid metabolism in R. jostii RHA1 predicted by MEME/MAST algorithm from the imperfect inverted repeat (IRR) motif found upstream of Rv0474 and hbhR genes of M. tuberculosis and M. marinum (Raghunandanan et al 2018;Raze et al 2020). IRR is analog to Box1.…”