dnaE2 expression promotes genetic diversity and bacterial persistence in mycobacterial biofilms

The complex cellular architecture and the microenvironments within the biofilm give rise to a population that is both physiologically and genetically heterogeneous. Transcriptome analysis of Mycobacterium smegmatis in biofilm culture and its transition phase into planktonic growth was performed to identify the genetic basis of heterogeneity in the biofilm. While there was an increase in the expression of mycobacterial mutasome consisting of dnaE2, imuA, and imuB in the biofilm, the mutation burden was less compared to the planktonic culture. Deletion of dnaE2 causes lower mutation frequency and bacterial fitness in comparison to the parental strain in biofilm culture. The expression of dnaE2 contributes to a slower bacterial growth rate, potentially promoting persister formation. Our study uncovers the multiple benefits of dnaE2 expression in biofilm such as increasing genetic diversity and reducing growth rate; both of which are necessary for mycobacterial survival and adaptation.