The Function Of The Mycobacterium Smegmatis WhiB3

Mycobacterium tuberculosis (Mtb) is a highly successful human pathogen. It confronts a more hostile environment during infection, including restricted access to nutrients, reduced oxygen tension and low pH stress. Therefore, Mtb must possess genetic mechanisms to facilitate integrated responses to multiple stresses. Recently, the whiB gene family, found only in Actinomycete genera, is extensively studied. It has confirmed that they played significant roles for Mycobacterium to response to environmental stresses. In the current study, using Mycobacterium smegmatis as a model, we studied the effects of whiB3 on mycobacterial growth and resistance. The major results are as follows:(1) A whiB3 knockout mutant strain of Msm has been constructed and the differences of cell shape and liquid culture characteristic were found between the wild type Msm and the mutant MsmΔwhiB3. MsmΔwhiB3 cells were significantly increased in length and it remained dispersed in liquid media compared to Wt Msm cells. (2) No obvious growth for MsmΔwhiB3 was observed both in 7.84 mM H2O2 and pH 4.5 conditions while Wt Msm cells grew well. (3) Complemention results found that Mtb homologous gene MtbwhiB3full almost could not re-establish the resistance phenotype of the knockout mutant strain of Msm. In contrast, several other genes such as MsmwhiB3full, MsmwhiB3ΔC, and MtbwhiB3ΔC showed complemental effects. (4) A substantial difference was detected between MsmwhiB3full and MtbwhiB3full on protecting mycobacterial genome stability. Mutation frequencies of several mutants and their complementation strains were totally different if comparing the effects of H2O2 (7.84 mM) on them.The whiB3 genes are conserved in Mycobacterium, and they play multiple roles in genes regulation and expresstion. The current study found that the mutant strain MsmΔwhiB3 showed considerable difference in many aspects if compared with the reported MtbΔwhiB3. This implies that the pathogen may have a unique regulatory mechanism. Interestingly, the function of mycobacterial whiB3 gene for the first time linked to the drug resistance. All these results would greatly contribute to a further understanding on the whiB3 function of Mycobacterium and the role in physiology and pathology.