The Formosan subterranean termite, Coptotermes formosanus Shiraki, is an aggressive, invasive termite species that has caused billions of dollars of damage across the United States for the past 50 years. Termites depend on intestinal microorganisms for cellulose digestion. Symbiotic microorganisms in the termite gut play key physiological functions such as cellulose and hemicellulose digestion, acetogenesis, hydrogenesis, methanogenesis, sulfate reduction, and nitrogen fixation. Additionally, intestinal microbes create suitable conditions for symbiotic protozoans through the production of nutrients and the maintenance of the pH and the anaerobic conditions in the gut. Although extensive research has been done on the symbiotic relationship of these termites and the microbes found in its gut, there is little information available on the role of facultative anaerobes in the gut. We isolated four enteric bacteria from the hindgut of Formosan subterranean termite, C formosanus. All isolates were facultative anaerobes and G-The isolates were identified as Serratia marcescens, Enterobacter aerogens, Enterobacter cloacae, and Citrobacter farmeri by using BIOLOG assay and fatty acid methyl ester analysis (FAME). Each isolate was characterized using sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and biochemical study. This is the first report on the presence of facultative microbes in termite gut. Results of this first study on facultative microbes in the termite gut indicate that the role of facultative organisms in the Formosan termite gut may be to scavenge oxygen and create anaerobic conditions for the anaerobic microorganisms, which are essential for digestion of cellulose consumed by the termite. (c) 2005 Elsevier Ltd. All rights reserved.