THE ROLE OF INTERACTIONS, SESSILE GROWTH, AND NUTRIENT AMENDMENTS ON THE DEGRADATIVE EFFICIENCY OF A MICROBIAL CONSORTIUM

A degradative microbial consortium consisting of at least nine bacteri al and one algal species was isolated from soil with diclofop methyl a s the sole carbon source. In continuous flow culture, the presence of the algae increased diclofop methyl degradation and removal by 36%. Ba tch culture experiments with C-14-labeled diclofop methyl confirmed al gal involvement in the mineralization of diclofop methyl as there was no significant difference in the amount of (CO2)-C-14 evolved by the b acterial consortium with and without the algal activity when the conso rtium was cultivated in the dark to inhibit algal growth, while 11% mo re (CO2)-C-14 was produced in the light by the algal-bacterial consort ium. Pure cultures isolated from the bacterial consortium could not in dividually mineralize diclofop methyl as the sole carbon source. Howev er, when supplied with an additional carbon source, two strains could mineralize diclofop methyl. Addition of either the complex growth medi um, or a cell-free filtrate from the algal-bacterial consortium to bat ch systems containing C-14-labeled diclofop methyl resulted in a signi ficant increase in the production of (CO2)-C-14 by the bacterial conso rtium, suggesting co-metabolism of diclofop methyl in the presence of a labile carbon source. Removal of diclofop methyl by the bacterial co nsortium was increased by 36% when a larger surface to volume ratio wa s provided by glass beads that allowed extensive biofilm formation. Th e requirement for exogenous carbon sources and the inability of isolat ed pure cultures to degrade diclofop methyl indicated that interspecie s interactions are necessary for degradation. The positive effect of s essile growth suggested that spatial organization of cells may also be important for degradation.