Suppressors of YpsA-mediated cell division inhibition in Bacillus subtilis

Although many bacterial cell division factors have been uncovered over the years, evidence from recent studies points to the existence of yet to be discovered factors involved in cell division regulation. Thus, it is important to identify factors and conditions that regulate cell division to obtain a better understanding of this fundamental biological process. We recently reported that in the Gram-positive organisms Bacillus subtilis and Staphylococcus aureus, increased production of YpsA resulted in cell division inhibition. In this study, we isolated spontaneous suppressor mutations to uncover critical residues of YpsA and the pathways through which YpsA may exert its function. Using this technique, we were able to isolate four unique intragenic suppressor mutations in ypsA (E55D, P79L, R111P, G132E) that rendered the mutated YpsA non-toxic upon overproduction. We also isolated an extragenic suppressor mutation in yfhS, a gene that encodes a protein of unknown function. Subsequent analysis confirmed that cells lacking yfhS were unable to undergo filamentation in response to YpsA overproduction. We also serendipitously discovered that YfhS may play a role in cell size regulation. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=193 SRC="FIGDIR/small/946632v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@1098d63org.highwire.dtl.DTLVardef@216f86org.highwire.dtl.DTLVardef@121050eorg.highwire.dtl.DTLVardef@d2ef3a_HPS_FORMAT_FIGEXP M_FIG C_FIG ABBREVIATED SUMMARYIn Bacillus subtilis, we discovered that increased expression of ypsA results in cell division inhibition and impairment of colony formation on solid medium. Colonies that do arise possess compensatory suppressor mutations. Analysis of one such suppressor mutation led us to a protein of unknown function, YfhS, which appears to play a role in regulating cell length and cell width.