Sulfur-specific microbial metabolism of organic compounds

Abstract

Efficient microbial metabolism of inorganic sulfur in coal has been known for some time. However, the microbial metabolism of organically bound sulfur is inefficient and constitutes the chief obstacle to the development of a viable process for the microbial desulfurization of coal. What is needed are microorganisms with the ability to remove sulfur from organic substrates while leaving the carbon intact: microorganisms capable of sulfur-specific metabolism. Studies of the microbial metabolism of organic sulfur compounds by naturally occurring bacterial cultures have resulted in the isolation of cultures that degrade these compounds but lack sulfur-specific metabolism. Research at this institution has resulted in the development of an experimental methodology for the purposeful isolation/development of bacterial cultures capable of sulfur-specific metabolism and the development of a sulfur-specific bioassay. Through the use of sulfur-limited continuous culture bioreactors, a mixed bacterial culture, IGTS7, was isolated and shown by GC/MS analyses to be capable of the sulfur-specific metabolism of a range of organic substrates. The removal of organic sulfur from coal by IGTS7 can be as high as 91%. However, IGTS7 is incapable of growth at the acidic pH typical of conditions conducive to the microbial metabolism of inorganic sulfur. Therefore, one strategy to develop a single-step microbial process for the complete desulfurization of coal would be to use genetic engineering techniques to isolate the genes that encode sulfur-specific metabolic functions for organic compounds from microorganisms such as IGTS7 and achieve enhanced expression of those functions in an acid-tolerant host.