Importance of Xanthobacter autotrophicus in toluene biodegradation within a contaminated stream

Toluene-degrading strains T101 and T102 were isolated from rock surface bio mass in a toluene-contaminated freshwater stream. These organisms were pres ent at a density of 5.5x10(6) cells/g of rock surface biomass. Both are aer obic, rod-shaped, Gram-negative, non-motile, catalase-positive, oxidase-pos itive, with yellow pigments, and can grow on benzene. Phylogenetic analyses show that strains T101 and T102 have 16S rDNA sequences identical to Xanth obacter autotrophicus. Fatty acid analyses indicate that they are different strains of the same species Xanthobacter autotrophicus, and that they have high levels of cis-11-octadecenoic acid and cis-9-hexadecenoic acid; 3-hyd roxyhexadecanoic acid is the major hydroxy fatty acid present. Strains T101 and T102 had maximal velocities (V-max) for toluene biodegradation of 3.8 +/- 0.5 and 28.3 +/- 2.2 mu moles toluene/mg(protein)-hr, and half-saturati on constants (K-s) of 0.8 +/- 0.5 and 11.5 +/- 2.4 mu M, respectively. Stra in T102 has a higher capacity than strain T101 to degrade toluene, and kine tic calculations suggest that strain T102 may be a major contributor to tol uene biodegradation in the stream.