A new toluene-producing bacterium, strain TA 4T (T = type strain), was isolated from anoxic sediments of a freshwater lake. The individual cells of this organism were nonmotile, gram-negative rods that were 0.9 to 1.2 by 2.5 to 3.2 microns. The optimum temperature and pH for growth were 22 degrees C and pH 7.2, respectively. The G+C content of the DNA was 49 mol%. Toluene was produced from phenylalanine, phenylpyruvate, phenyllactate, and phenylacetate, and phenol was produced from tyrosine. Both the presence of a carbon source and the presence of a toluene precursor were essential for initiation of toluene production. Bacterial growth occurred under oxic and anoxic conditions. Acetate, ethanol, and formate were the major fermentation products of the bacterium when it was grown on glucose. The major lipoquinones were ubiquinone 8 and menaquinone 8 under both oxic and anoxic growth conditions. On the basis of the results of a 16S ribosomal DNA sequence analysis, we concluded that this organism is a member of the gamma subclass of the Proteobacteria, and we suggest the name Tolumonas auensis for this species.