MODIFICATION OF RHIZOBACTERIAL POPULATIONS BY ENGINEERING BACTERIUM UTILIZATION OF A NOVEL PLANT-PRODUCED RESOURCE

The ability to catabolize distinct nutrients produced by a plant may b e a factor in the successful colonization of that host by a bacterium when in competition with other rhizosphere microorganisms. We tested t his hypothesis by examining the influence of a novel substrate produce d by a transgenic plant on root colonization by near-isogenic bacteria , differing only in their ability to use the resource. When inoculated alone, both bacteria colonized the roots of the normal and transgenic plants with equal kinetics and to indistinguishable levels. When the two bacteria were coinoculated, the catabolizer reached a population d ensity significantly higher than that of the noncatabolizer on the roo ts of the resource-producing plant. No such advantage was observed on the roots of normal plants. These results support the theory that reso urces produced and exuded by a plant host can confer a selective advan tage to microorganisms that use the substrate.