Role of FtsEX in cell division of Escherichia coli: viability of ftsEX mutants is dependent on functional SufI or high osmotic strength

Centre for Cellular and Molecular Biology, Hyderabad India 500007

^* To whom correspondence should be addressed. Email: manjula{at}ccmb.res.in.

	Abstract

In Escherichia coli, at least twelve proteins FtsZ, ZipA, FtsA, FtsE/X, FtsK, FtsQ, FtsL, FtsB, FtsW, FtsI, FtsN and AmiC are known to localize to the septal ring in an interdependent and sequential pathway to coordinate the septum formation at the midcell. FtsEX complex is the latest recruit of this pathway and unlike other division proteins it is shown to be essential only on media with low salt. In this study, it is shown that null ftsEX mutations are not only salt-remedial but also osmoremedial, which suggests that FtsEX may not be involved in salt transport as previously thought. Increased coexpression of cell division proteins FtsQ-FtsA-FtsZ or FtsN alone restored the growth defects of ftsEX mutants. ftsEX deletion exacerbated the defects of most of the mutants affected in Z-ring localization and septal assembly; however, ftsZ84 allele was a weak suppressor of ftsEX. The viability of ftsEX mutants in high-osmolarity conditions was shown to be dependent on the presence of a periplasmic protein SufI, a substrate of twin-arginine translocase. In addition, SufI in multiple copies could substitute for the functions of FtsEX. Taken together, these results suggest that FtsE and FtsX are absolutely required for the process of cell division in conditions of low osmotic strength for the stability of the septal ring assembly, and that during high-osmolarity conditions the FtsEX and SufI functions are redundant for this essential process.