AN ISOELECTRIC-FOCUSING STUDY OF THE EFFECT OF METHYL-ESTERIFIED PECTIC SUBSTANCES ON THE PRODUCTION OF EXTRACELLULAR PECTIN ISOENZYMES BY SOFT-ROT ERWINIA SPP

The production of extracellular pectic isoenzymes by seven strains of soft rot bacteria, Erwinia carotovora subsp. carotovora, E.c. atrosept ica and E. chrysanthemi, when grown in media containing four different pectic substances with different degrees of methylation or with potat o tuber cell-wall extract was examined by isoelectric focusing activit y staining. In addition to the isoenzymes of pectate lyase, polygalact uronase and pectin methyl esterase produced constitutively or followin g induction by polygalacturonic acid (PGA) and coded by known genes, b etween two and seven novel isoenzymes of the three enzymes with a wide r pi range were apparently induced by the pectins and cell-wall extrac t. Pectin lyase, which is induced in vitro by DNA-damaging agents, was not produced in the absence of mitomycin C in a medium containing PGA but up to two isoenzymes were found with pectin or cell-wall extract. In contrast, cellulase isoenzyme production was not affected by pecti n or cell-wall extract. A greater number of novel isoenzymes of all pe ctic enzymes except pectin lyase tended to be produced in media contai ning Link pectin, which is PGA methylated to 98%, than the other pecti c substances and cell-wall extract. Pectate lyase and polygalacturonas e were induced by pectin lyase-degraded products of highly methylated pectin but not by PGA in an E. chrysanthemi strain with all its known pel and peh genes mutated. The results suggest that the production of novel pectic isoenzymes could be related to the presence of CH3+ group s and that their induction differs from that for isomers induced by PG A-degraded products and DNA-damaging agents or produced constitutively .