TRANSITION OF PHOSPHITE TO PHOSPHATE IN SOILS

Abstract

The nature of oxidation of phosphite added to soil was investigated using both chemical and biological assays to determine the amount of oxidation. Oxidation proceeded only when microbial activity was not restricted by the presence of toluene and when a suitable energy source was present. Soil microorganisms removed phosphite from simple synthetic culture solns. Autolysis of these microbial cells released considerable inorganic phosphate which could only have been derived from phosphite. Phosphite uptake and phosphate release also occurred with soil organisms growing on various C and N subtrates and with pure cultures of known bacteria, fungi, and actinomycetes. The ability to utilize and oxidize phosphite seems to be a characteristic possessed by some, if not many, types of microorganisms. When phosphate and phosphite were in the same culture, the phosphate was removed from soln. by bacteria before appreciable amts. of the phosphite were removed. The P lost from soln. as phosphite during microbial growth was recovered by the wet digestion of the washed bacterial cells. Phosphite oxidation is not a mere surface phenomenon of microbial cells since washed cells suspended in distilled water and phosphite showed no oxidation of phosphite.