Calystegine degradation capacities of microbial rhizosphere communities ofZea mays (calystegine-negative) and Calystegia sepium (calystegine-positive)

Calystegines are tropane alkaloids produced by the roots of a few plant spe cies, A bioassay was developed to identify roots with a microbial rhizosphe re community capable of calystegine degradation (i.e. MCD roots). In a fiel d survey, the proportion of MCD roots of Zea mays (calystegine-negative) va ried from 20 to 80%. In field experiments, the proportions of MCD roots of Z. mays and Calystegia sepium (calystegine-positive) grown in a particular plot were similar to each other but varied with time and, overall, were hig her than those of Z. mays roots from adjacent plots free of C. sepium. In a utoclaved soil, no root of C. sepium or Z. mays plants propagated as seeds was MCD, indicating that calystegine-degrading microorganisms were not seed -borne. However, MCD roots were found as early as I day after planting of r hizomes of C. sepium in autoclaved soil or planting of axenic seedlings of either plant in natural soil microcosms. In total, microorganisms capable o f degrading calystegines were harboured not only in the rhizosphere of the calystegine-producing plant but also in that of the calystegine-negative pl ant and probably in bulk soil. (C) 1999 Federation of European Microbiologi cal Societies. Published by Elsevier Science B.V. All rights reserved.