Calystegine degradation capacities of microbial rhizosphere communities of Zea mays (calystegine-negative) and Calystegia sepium (calystegine-positive)
Calystegines are tropane alkaloids produced by the roots of a few plant species. A bioassay was developed to identify roots with a microbial rhizosphere community capable of calystegine degradation (i.e. MCD roots). In a field survey, the proportion of MCD roots of Zea mays (calystegine-negative) varied 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 higher than those of Z. mays roots from adjacent plots free of C. sepium. In autoclaved 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 1 day after planting of rhizomes of C. sepium in autoclaved soil or planting of axenic seedlings of either plant in natural soil microcosms. In total, microorganisms capable of degrading calystegines were harboured not only in the rhizosphere of the calystegine-producing plant but also in that of the calystegine-negative plant and probably in bulk soil.