Bioaccumulation of the herbicide diclofop in extracellular polymers and its utilization by a biofilm community during starvation

Abstract

Continuous-flow cell systems were used to cultivate a degradative biofilm community with the herbicide diclofop methyl as the sole carbon and energy source. The aromatic character of this compound and its breakdown products enabled direct visualization of their accumulation in the biofilm matrix. This accumulation could be inhibited by addition of a more labile carbon source to the culture medium or by inhibition of cell activity. The fluorescence of diclofop-grown biofilms remained constant after 14 to 21 days but decreased with time when diclofop was omitted from the irrigation solution. However, this decrease was inhibited by cyanide, indicating either utilization or release of accumulated diclofop when the cells were viable. Subsequent experiments with [14C]diclofop also indicated that decreased fluorescence in the absence of an exogenous carbon source resulted from degradation of adsorbed diclofop and its breakdown products by the biofilm bacteria. These results demonstrate that biofilm exopolymers can facilitate storage of nutrients for subsequent mineralization during periods of carbon limitation.