SUPPRESSION OF THE LETHAL EFFECT OF ACIDIC-PHOSPHOLIPID DEFICIENCY INESCHERICHIA-COLI BY BACILLUS-SUBTILIS CHROMOSOMAL LOCUS YPOP

An acidic-phospholipid deficiency caused by the pgsA3 allele that enco des a defective phosphatidylglycerophosphate synthase in Escherichia c oli is lethal. The only known mutations that suppress this lethality f ully hare been related to the major outer-membrane lipoprotein. We iso lated a Bacillus subtilis chromosomal locus that suppresses the lethal ity when harbored in a low copy-number plasmid, without restoring the synthase activity or phospholipid composition to normal. The locus was first recognized to suppress the conditional lethality of E. coli YA5 512 (pgsA3) that harbored an unidentified mutation(s), allowing its gr owth in LB medium but not in media of lower osmolarities. The locus wa s then found to suppress the lethality of pgsA3 in wild-type E. coli W 3110. This locus, named ypoP in the database, had 37% nucleotide ident ity with the E. coli mprA gene, but the amplification of mprA had no s uppressive effect. Plasmid pPOP1 containing ypoP completely prevented the decrease in the amount of a porin protein, OmpF, in the outer memb rane and also cell mucoidy caused by pgsA3. The mechanisms underlying these unusual effects are discussed in relation to a putative stress s ignal(s) generated by the acidic-phospholipid deficiency.