Inhibition by polyphosphate of phytopathogenic polygalacturonases from Botrytis cinerea

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Abstract
Polygalacturonase activity from the phytopathogenic fungus Botrytis cinerea was inhibited in vitro by extracellular polyphosphate from Streptomyces sp. A50, as well as other polyphosphates of biological and chemical origin. The extent of inhibition increased with polyphosphate chain length between 20 and 100 Pi residues. Although the activity of polygalacturonase from B. cinerea appeared not to depend on the presence of cations, inhibition was partially blocked by divalent cations such as Mg2+or Ca2+. Production of polyphosphate in Streptomyces sp. A50 was followed by chemical measurements, as well as by in vivo 31P-NMR analysis. During the first 2 days of growth, polyphosphate accumulated within the cells, after which it appeared in the broth as an extracellular product. A maximum concentration of extracellular polyphosphate (1 mM Pi equivalent) was reached, corresponding to about 25% of the input Pi. NMR analysis suggested that the intracellular form of polyphosphate exists as a mobile soluble pool. In contrast, the extracellular form of polyphosphate appears to be complexed with cations.Key words: polygalacturonase, polyphosphate, Botrytis cinerea, Streptomyces, 31P-NMR.