The effect of alterations in fatty acid composition and fluidity of cell membranes on the accumulation of PCB congener 2,2,5,5'-tetrachlorobiphenyl (TeCB) by Ralstonia eutropha (formerly Alcaligenes eutrophus) H850 was studied. Cells of R eutropha H850 grown on either biphenyl or fructose were used. Significant increases in saturated fatty acid composition and decreases in membrane fluidity of bacteria grown on biphenyl at 28degreesC were observed compared with those grown on fructose at 17 or 28degreesC. The ratio of saturated fatty acids to unsaturated fatty acids and membrane fluidity of R eutropha H850 grown on biphenyl at 28degreesC resembled those of cells grown on fructose at 37degreesC. No inhibition effect of the uncoupler 2,4-dinitrophenol (2,4-DNP) on TeCB accumulation was observed, suggesting an energy-independent mechanism for TeCB accumulation in cells of R eutropha H850. The amount of TeCB accumulated was considerably higher in R eutropha H850 grown on fructose at 17 and 28degreesC than when grown on biphenyl at 28degreesC. Similar amounts of TeCB accumulated in bacteria grown on biphenyl at 28degreesC as compared with those grown on fructose at 37 C. These results suggest the alterations in fatty acid composition and membrane fluidity of R eutropha H850 may affect the accumulation of TeCB.