Nitrogen-fixing Enterobacter agglomerans isolated from guts of wood-eating termites

Abstract

Two strains of facultatively anaerobic, N2-fixing bacteria were isolated from guts of Coptotermes formosanus and identified as E. agglomerans. The DNA base composition of isolates was 52.6 and 53.1 mol% guanine plus cytosine. Both isolates and a known strain of E. agglomerans carried out a mixed acid type of glucose fermentation. N2 fixation by E. agglomerans was inhibited by O2; consequently, N2 served as an N source only for cells growing anaerobically in media lacking a major source of combined N. Peptone, NH4Cl or KNO3 served as an N source under either aerobic or anaerobic conditions. It was estimated that 2 .times. 102 cells of E. agglomerans were present per termite gut. This value was 100-fold lower than expected, based on N2 fixation rates of E. agglomerans in vitro and that of the intact termites. Low recoveries of E. agglomerans may be related to the marked decrease in N2 fixation rates observed when intact termites or their extracted guts were manipulated for the isolation of bacteria. The N2-fixing activity of E. agglomerans may be important to the N economy of C. formosanus.