Cometabolism of 17α-ethynylestradiol by nitrifying bacteria depends on reducing power availability and leads to elevated nitric oxide formation

•NO increased during 17α-ethynylestradiol (EE2) cometabolism by N. europaea.•nirK cluster genes were up-regulated during EE2 cometabolism by N. europaea.•EE2 cometabolism depends on reducing power supplied by ammonia oxidation.•EE2 cometabolic kinetics were estimated considering reductant availability.•Nine transformation products of EE2 were identified including five newly reported.