MICROBIAL DECOMPOSITION OF FERULIC ACID IN SOIL

The suppression of plant growth by different phenolic acids is well known. This work was designed to determine if ferulic acid, a known phenolic inhibitor of plant growth, accumulates in the soil and if soil microorganisms could be isolated that metabolize it. Over 99% of the extractable ferulic acid was lost from decaying hack, berry leaves in 300 days. During this time the amount in the top 15 cm of soil remained fairly constant at about 30 ppm, except for the March sample which was significantly higher than the rest. Addition of ferulic acid to soil caused an increase in CO2 evolution and in numbers of a select group of microorganisms. Rhodotorula rubra and Cephalosporium curtipes, which actively metabolize ferulic acid, were isolated, but the metabolic pathways employed appear to be different from the reported one. The reported pathway for ferulic acid breakdown is ferulic acid to vanillic acid to protocatechuic acid to beta-keto-adipic acid. Rhodotorula rubra was found to convert ferulic acid to vanillic acid, but no evidence was found for utilization of the rest of the pathway. Cephalo-sporium curtipes appears to use a different pathway or to metabolize intermediate compounds rapidly without accumulating them, because no phenolic compounds were found during the breakdown of ferulic acid. The presence in the soil of microorganisms that metabolize ferulic acid and other phenolic acids is ecologically significant because such organisms prevent long-term accumulations of these substances, which are toxic to many other microorganisms and higher plants.