An isoelectric focusing study of the effect of methyl‐esterified pectic substances on the production of extracellular pectin isoenzymes by soft rot Erwinia spp.

Abstract

The production of extracellular pectic isoenzymes by seven strains of soft rot bacteria, Erwinia carotovora subsp. carotovora, E.c. atroseptica and E. chrysanthemi, when grown in media containing four different pectic substances with different degrees of methylation or with potato tuber cell‐wall extract was examined by isoelectric focusing activity staining. In addition to the isoenzymes of pectate lyase, polygalacturonase and pectin methyl esterase produced constitutively or following induction by polygalacturonic acid (PGA) and coded by known genes, between two and seven novel isoenzymes of the three enzymes with a wider pI range were apparently induced by the pectins and cell‐wall extract. 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 pectin or cell‐wall extract. A greater number of novel isoenzymes of all pectic enzymes except pectin lyase tended to be produced in media containing Link pectin, which is PGA methylated to 98%, than the other pectic substances and cell‐wall extract. Pectate lyase and polygalacturonase were induced by pectin lyase‐degraded products of highly methylated pectin but not by PGA in an E. chrysanthemi strain with all its known pei and peh genes mutated. The results suggest that the production of novel pectic isoenzymes could be related to the presence of CH+3 groups and that their induction differs from that for isomers induced by PGA‐degraded products and DNA‐damaging agents or produced constitutively.