Microbial growth on mercaptosuccinic acid

Abstract

Using enrichment culture technics a species of Alcaligenes (M₁) was isolated from soil which was able to utilize mercaptosuccinic acid (MS) as a sole source of carbon, sulfur, and energy. Growth on a MS–salts basal medium was not significantly enhanced by single supplements of B-vitamins or by yeast extract. Comparative studies on succinate and MS oxidation by Alcaligenes and Pseudomonas aeruginosa indicated that MS was an inhibitor of succinate oxidation by resting cells of both microorganisms when they were grown in a medium lacking mercaptosuccinic acid such as a succinate–salts basal. However, when M₁ was grown on MS, it was able to oxidize both succinate and MS, thereby indicating that the MS oxidase system was inducible. In addition, the MS oxidase system in cell-free extracts of M₁ was relatively insensitive to 10–30 μmoles of malonate, whereas the succinoxidase system was inhibited 66% by 30 μmoles of the inhibitor. Cell-free extracts of succinate-grown cells of P. aeruginosa were unable to oxidize MS, indicating that the inactivity of resting cells was not due to a permease problem. Investigation of the metabolic fate of the sulfur moiety of MS by growing cells of M₁ indicated that all of the available sulfur was liberated as inorganic sulfate, while no free sulfide was detected. Thiosulfate sulfurtransferase (rhodanese) was detected in extracts from cells grown both with and without mercaptosuccinic acid. However, growth in the MS medium enhanced the production of rhodanese approximately 40%. In addition, thiosulfate oxidase activity was also detected in resting cells and cell-free extracts prepared from MS-grown cells, but not from cells grown without mercaptosuccinic acid.