Our analyses of the ΔrodZ mutant showed that the absence of RodZ leads to the reduced expression of most of the flagella genes, but not of their master regulator, which seems to suggest that RodZ does not function as a regulatory factor for this large network. It seems find more that the reduced expression could be due to stress signals from a defective cell wall. The rodZ mutant was nonmotile, but possessed flagella that were indistinguishable from those of the wild type. The expression of the motA operon required for membrane-bound components of flagellar motor and chemotactic response was most severely reduced in the mutant (Table

1). This might explain the above-mentioned phenotype of the mutant because mutations in motA and motB impaired the motility, but not the assembly Galunisertib purchase of flagellum (Blair & Berg, 1990). Cells of the rodZ mutant, however, were able to move actively in liquid medium, although the number of active cells was much less than that in the wild type. Therefore, the nonmotile phenotype might be due to both defective motor synthesis and loss of proper chemotactic function. It is also conceivable

that the weakened membrane structure and/or the altered cell shape hindered the movement of cells through soft agar, where more pressure is expected than in liquid medium. We have confirmed that rodZ and ispG comprise an operon and the absence of RodZ apparently affected the expression of ispG. Because its

overproduction is toxic to cells (GenoBase: http://ecoli.aist-nara.ac.jp/index.html), IspG might play another role in the peptidoglycan metabolism in addition to isoprene synthesis (Campos et al., 2001), although it has not yet been revealed in E. coli. In Providencia stuartii, a homologue of ispG termed aarC regulates the expression of 2′-N-acetyltransferase that contributes to the O-acetylation of peptidoglycan, and a missense mutant of aarC showed a phenotype similar to the rodZ mutant (Rather et al., 1997). O-acetylation influences the activity of lytic transglycosylases involved in the biosynthesis and turnover of peptidoglycan (reviewed Metformin supplier in Scheurwater et al., 2008). Therefore, RodZ might function in the fine-tuning of peptidoglycan biosynthesis. Plasmid pBADs-rodZΔHTH could rescue neither the sphere cell shape nor the nonmotile phenotype contrary to the recent reports by Shiomi et al. (2008) and Bendezúet al. (2009). We assume that this discrepancy is due to the amount of ΔHTH molecules expressed, because we occasionally observed elongated cells among the ΔrodZ mutant carrying plasmid prodZ-1-ΔHTH that should produce more proteins than pBADs-rodZΔHTH (Fig. 1g). The growth rate of the ΔrodZ mutant with this plasmid was also higher than that with pBADs-rodZΔHTH.