Nitrogen fixation by cellulolytic communities at aerobic‐anaerobic interfaces in straw

Microbial communities involved in both cellulolysis and nitrogen fixation were isolated from decomposing straw. Cellulolytic activity appeared restricted to fungal isolates, predominantly species of Penicillium and Fusarium , growing in the presence of oxygen. Bacteria isolated under anaerobic conditions on nitrogen‐free media were identified exclusively as Clostridium butyricum . Enterobacters isolated on media containing fixed nitrogen, particularly Enterobacter cloacae , might also be involved in nitrogen fixation when growing under conditions of restricted aeration. Anaerobic or facultative anaerobic nitrogen‐fixing bacteria are thought to be sustained by the products of cellulolytic enzymes from aerobic fungi.