Biotechnology and microbiology of coal degradation

For several years it has been known that fungi and bacteria can attack and even liquefy low rank coals. This review covers the progress in coal biotec hnology and microbiology, mainly during the last decade, from describing th e first effects to elucidating the mechanisms used by the microorganisms. M ore than one mechanism is responsible for microbial coal degradation/liquef action: oxidative enzymes (peroxidases, laccases), hydrolytic enzymes (este rases), alkaline metabolites and natural chelators. Due to the heterogeneou s structure of coal, which is described in one section, and for economic re asons the review focuses on the enzymatic depolymerization of brown coal. A pproaches which seem not so promising are discussed (anaerobic, reductive p athways, chemical pretreatment). Finally the possible applications and prod ucts in this field are summarized, as lignite with a worldwide production o f about 940 million tons a year will continue to play an important economic role in the future.