Abstract
SUMMARY Cultures of 10 of 19 nomenspecies of the genus Xanthomonas liquefied a nutrient pectate gel. None of the 19 nomenspecies produced either hydrolytic polygalacturonase or pectin trans-eliminase. Seventeen of the nomenspecies showed a detectable, at times weak, pectinesterase activity. Seven of the 10 pectate-liquefying nomenspecies excreted polygalacturonic acid trans-eliminase in culture fluids containing pectin as growth substrate. The enzymo-logical basis, if any, is not at present known for the liquefaction of the nutrient pectate gel in the remaining three xanthomonads, which all lacked both the hydrolytic and the eliminative enzymes. Pectinesterase and polygalacturonic acid trans-eliminase were produced inducibly on pectin by most X. campestris cultures which were examined; some strains of this phytopathogen formed polygalacturonic acid trans-eliminase constitutively on glucose, but pectinesterase was never constitutive. The polygalacturonic acid trans-eliminase excreted by the tested xanthomonads degraded polygalacturonic acid in a random manner. The major end-products were unsaturated di- and tri-galacturonic acids, accompanied by lesser amounts of saturated mono-, di-, and tri-galacturonic acids.
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