[No authors listed]
Lipoteichoic acid (LTA) is an important cell envelope component of Gram-positive bacteria. Bacillus subtilis has four homologous genes for LTA synthesis: ltaS (yflE), yfnI, yqgS and yvgJ. The products LtaS (YflE), YfnI and YqgS are bona fide LTA synthetases, whereas YvgJ functions only as an LTA primase. To clarify whether defects in LTA on the cell envelope trigger extracytoplasmic function (ECF) sigma factors, mRNA levels of the autoregulated ECF sigma factors in cells with singly and multiply deleted alleles of the ltaS homologues were examined by real-time RT-PCR. This revealed that sigM and sigX were induced in cells with a null allele of ÎltaS and ÎyfnI, respectively, and that no ECF sigma factor was induced in cells with a single null allele of ÎyqgS or ÎyvgJ. In cells with double null alleles (ÎltaS and ÎyfnI), sigW and ylaC were induced in addition to sigM and sigX. Cells with triple null alleles (ÎltaS ÎyfnI and ÎyqgS) showed a pattern of induction similar to that of the double null. In cells with quadruple null alleles, sigV and sigY were newly induced. Cells with ÎltaS had approximately 1/4 the diglucosyldiacylglycerol and over 10 times the CDP-diacylglycerol of wild-type cells. Compensatory elevation of the mRNA level of other homologues was observed (in ÎltaS cells the level of yfnI was elevated; in ÎyfnI cells that of yqgS and yvgJ was elevated; both were even higher in ÎltaS ÎyfnI cells). In ÎltaS cells, the mRNA level of yfnI was corroborated to be regulated by Ï(M), which is activated in the null mutant cells. In ÎyfnI cells, the mRNA levels of yqgS and yvgJ reverted to less than those of wild-type when a defective sigX allele was introduced. Since sigX was activated in cells with ÎyfnI, this suggests that the induction of yqgS and yvgJ is dependent on Ï(X). The LTAs produced by the four ltaS homologues seem to play distinct physiological roles to maintain the full function of LTA on the B. subtilis cell envelope.
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