Nocardioides sp. strain JS614 grows on the C-2 alkenes ethene (Eth), vinyl chloride, and vinyl fluoride as sole carbon sources. The presence of 400-800 mu M ethene oxide (EtO) extended the growth substrate range to propene (C-3) and butene (C-4). Propene-dependent growth of JS614 was CO2 dependent and was prevented by the carboxylase/reductase inhibitor 2-bromoethanesulfonic acid, sodium salt (BES), while growth on Eth was not CO2 dependent or BES sensitive. Although unable to promote growth, both propene and propene oxide (PrO)-induced expression of the genes encoding the alpha subunit of alkene monooxygenase (etnC) and epoxyethane CoM transferase (etnE) to similar levels as did Eth and EtO. Propene was transformed by Eth-grown and propene-grown/EtO-induced JS614 to PrO at a rate 4.2 times faster than PrO was consumed. As a result PrO accumulated in growth medium to 900 mu M during EtO-induced growth on propene. PrO (50-100 mu M) exerted inhibitory effects on growth of JS614 on both acetate and Eth, and on EtO-induced growth on Eth. However, higher EtO concentrations (300-400 mu M) overcame the negative effects of PrO on Eth-dependent growth.