To depolymerize plant pectin, the phytopathogenic enterobacterium produces five isoenzymes of pectate lyases encoded by the five genes and In all genes involved in pectin degradation are specifically controlled by the KdgR repressor and are induced in the presence of a pectin catabolic product, 2-keto-3-deoxygluconate (KDG). Transcription of the pectinase genes is dependent on many environmental conditions. Transcriptional fusions present on low-copy-number plasmids were used to study the regulation of the genes in a heterologous host, Some physiological regulations that take place in are conserved in The five fusions in are affected by growth phase, catabolite repression and anaerobic growth conditions and are induced in the presence of galacturonate, a sugar whose catabolism leads to the formation of KDG, the inducer of transcription in Expression of increased with the osmolarity of the culture medium. In contrast, the regulation of expression by temperature or nitrogen starvation, observed in was not conserved in suggesting that the mechanisms responsible for these regulations are specific to Analysis of different mutants allowed some regulators affecting the transcription of the genes to be identified. In the growth-phase regulation of the genes is not dependent on the RpoS sigma factor and the gene is not involved in the increase of expression in oxygen-limited conditions. The gene involved in the regulation of numerous genes, appears to affect expression but the effects of mutations are not related to osmoregulation. In contrast, this analysis clearly demonstrates the interchangeability of two regulatory systems of and the global control exerted by the catabolite activator protein CAP and the specific regulation mediated by the KdgR repressor.


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