Abstract
We investigated the biodegradation of two bipyridinium herbicides, paraquat and diquat, by Lipomyces starkeyi. This yeast was able to grow in a synthetic medium containing the herbicides as sole nitrogen sources. Growth with paraquat was more rapid than with diquat. Both herbicides were consumed from the medium within the logarithmic phase. The yeasts seemed to have low conversion activities from [methyl-14C]paraquat or [ethylene-14C]diquat to 14CO2, even when they were grown in the absence of the herbicides. Paraquat added to the culture medium augumented the degradation of both [14C]paraquat and [14C]diquat. On the other hand, diquat added to the medium did not augument degradation of the herbicides. Moreover, the addition of diquat together with paraquat abolished the augumentation caused by paraquat. The protein composition of L. starkeyi was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cells in the logarithmic phase contained more proteins than those in the stationary phase. In addition, the protein patterns of the cells in the logarithmic phase were found to vary with the nitrogen sources, i.e. paraquat, diquat and NH4Cl. The mechanisms which regulate the catabolism of the two herbicides are discussed.
