Growth Characteristics of a Species of Lipomyces and its Degradation of Paraquat

Abstract

Summary: A Lipomyces sp. of soil yeast, probably of the ‘starkeyi’ or ‘lipofer’ type, degraded paraquat over a wide range of pH and temperatures, extreme values of which reduced growth but not paraquat degradation. The organism withstood high concentrations of the herbicide. Growth in nitrogen-depleted broth amended with paraquat showed a lag phase of about 24 h. There was no lag with (NH4)2SO4 either alone or with paraquat, but in the latter case paraquat degradation was delayed for 24 h. A 24 h exposure to paraquat and a carbon source was necessary for synthesis of the paraquat-catabolizing system. The organism grew well on soil extract and malt extract and media containing (NH4)2SO4 or NH4NO3 as nitrogen sources; it grew with urea or NaNO2 after a lag of 24 h or longer, but not on biuret or NaNO3. Atmospheric N2 was fixed in the presence of added molybdate. The presence of alternative nitrogen sources did not prevent or delay paraquat degradation. A variety of mono-, di-and polysaccharide materials was used as carbon and energy source. Growth was not obtained with powdered cellulose, carboxy-methyl-cellulose, lactose or paraquat as sole carbon source. The organism was unable to ferment carbohydrates or degrade paraquat anaerobically; it degraded commercial formulations of paraquat, but growth and degradation were affected by increasing concentrations of formulating additives.