CHARACTERIZATION OF EXTRACELLULAR BACTERIAL ENZYMES WHICH DEPOLYMERIZE A SOLUBLE LIGNITE COAL POLYMER

Several Gram negative and positive soil bacteria, isolated by an enrichment technique in a liquid minimal medium containing water-soluble lignite coal polymer as a sole source of carbon and energy, were screened for their abilities to depolymerize coal when growing in peptone broth containing soluble coal. One Gram positive and three Gram negative strains significantly depolymerized the coal within 3-6 days. These strains were screened for the production of extracellular coal depolymerizing enzymes. Each bacterium, including Gram negative strains DLC-BB2, DLC-62 and DLC-63/9, and Gram positive strain DLC-21, produced lignite depolymerizing enzymes. Extracellular filtrates from 3-day cultures grown in peptone medium supplemented with an inducing level of soluble coal polymer, contained an enzymatic activity which caused significant depolymerization of the coal polymer after 4 h of incubation of enzyme with coal (30-degrees-C), as shown by high performance liquid chromatography (h.p.l.c.). Each bacterium produced similarly acting enzymes which progressively converted the principal broad coal polymer peak of about MW 174000 into a much sharper peak of about 113000. In some cases, even lower molecular weight products appeared upon prolonged incubation of the reaction mixtures. The activities were inactivated by boiling of culture supernatants. While chemical analyses of enzymatically depolymerized coal products indicated that the depolymerization was non-oxidative, the specific type(s) of enzymes involved in the depolymerization remain to be identified. The results show that non-oxidative, enzymatic depolymerization of coal is possible.