Fourteen phylogenetically diverse 17beta-estradiol-degrading bacteria (strains KC1-14) were isolated from activated sludge of a wastewater treatment plant. These isolates widely distributed among eight different genera--Aminobacter (strains KC6 and KC7), Brevundimonas (strain KC12), Escherichia (strain KC13), Flavobacterium (strain KC1), Microbacterium (strain KC5), Nocardioides (strain KC3), Rhodococcus (strain KC4), and Sphingomonas (strains KC8-KC11 and KC14)--of three Phyla: Proteobacteria, Actinobacteria, and Bacteroidetes. All 14 isolates were capable of converting 17beta-estradiol to estrone, but only three strains (strains KC6, KC7, and KC8) showed the ability to degrade estrone. Only strain KC8 could use 17beta-estradiol as a sole carbon source. Based on the degree of estrogens being transformed and the estrogenicity of metabolites and/ or end products of estrogen degradation, three different degradation patterns (patterns A-C) were observed from degradation tests using resting cells. Eleven out of 14 isolates showed degradation pattern A, where 17beta-estradiol was stoichiometrically converted to estrone. Estrone was confirmed to be a degradation product of 17beta-estradiol; however, estrone was not further degraded during the course of experiments. Strains KC6 and KC7 exhibited degradation pattern B, where both 17beta-estradiol and estrone were degraded, with slower 17beta-estradiol degradation rates than those observed in pattern A. Strain KC8 was the only strain exhibited degradation pattern C, where 17beta-estradiol and estrone were rapidly degraded within 3 days. No residual 17beta-estradiol and estrone or estrogenic activity was detected after 5 days, suggesting that strain KC8 could degrade 17beta-estradiol into nonestrogenic metabolites/end products. Strains KC6-8 exhibited nonspecific monooxygenase activity but not nonspecific dioxygenase activity. However, the relationship between nonspecific monooxygenase activity and its estrogen degradation ability was unclear.