Identification and functional annotation of mycobacterial septum formation genes using cell division mutants of Escherichia coli

Septum site placement in Mycobacteria - identification and characterisation of mycobacterial homologues of Escherichia coli MinD

A major virulence trait of Mycobacterium tuberculosis (M. tb) is its ability to enter a dormant state within its human host. Since cell division is intimately linked to metabolic shut down, understanding the mechanism of septum formation and its integration with other events in the division pathway is likely to offer clues to the molecular basis of dormancy. The M. tb genome lacks obvious homologues of several conserved cell division proteins, and this study was aimed at identifying and functionally characterising mycobacterial homologues of the E. coli septum site specification protein MinD (Ec MinD). Sequence homology based analyses suggested that the genomes of both M. tb and the saprophyte Mycobacterium smegmatis (M. smegmatis) encode two putative Ec MinD homologues - Rv1708/MSMEG_3743 and Rv3660c/ MSMEG_6171. Of these, Rv1708/MSMEG_3743 were found to be the true homologues, through complementation of the E. coli ∆minDE mutant HL1, overexpression studies, and structural comparisons. Rv1708 and MSMEG_3743 fully complemented the mini-cell phenotype of HL1, and over-expression of MSMEG_3743 in M. smegmatis led to cell elongation and a drastic decrease in c.f.u. counts, indicating its essentiality in cell-division. MSMEG_3743 displayed ATPase activity, consistent with its containing a conserved Walker A motif. Interaction of Rv1708 with the chromosome associated proteins ScpA and ParB, implied a link between its septum formation role, and chromosome segregation. Comparative structural analyses showed Rv1708 to be closer in similarity to Ec MinD than Rv3660c. In summary we identify Rv1708 and MSMEG_3743 to be homologues of Ec MinD, adding a critical missing piece to the mycobacterial cell division puzzle.

An Escherichia coli expression model reveals the species-specific function of FtsA from Neisseria gonorrhoeae in cell division

Escherichia coli (Ec) has been used to study the function of cell division proteins from different microorganisms, especially when genetic tools are limited for studying these proteins in their native hosts. The expression of ftsA from Neisseria gonorrhoeae (Ng) disrupted cell division in E. coli resulting in a significant increase in cell length. In some cells, FtsANg localised to the division site and the poles of E. coli cells, but the majority of cells showed no specifical localisation. FtsANg did not complement an E. coli ftsA mutant strain. Bacterial two-hybrid and GST pull-down assays indicated that FtsANg interacted with FtsNEc, but no other cell division proteins from E. coli. This interaction was mediated through the 2A and 2B subdomains of FtsANg. This evidence suggests that the function of FtsANg is species specific.