A new strain isolated from soil utilizes cyclopropanecarboxylate as the sole source of carbon and energy and was identified as Rhodococcus rhodochrous (H. Nishihara, Y. Ochi, H. Nakano, M. Ando, and T. Toraya, J. Ferment. Bioeng. 80:400-402, 1995). A novel pathway for the utilization of cyclopropanecarboxylate, a highly strained compound, by this bacterium was investigated. Cyclopropanecarboxylate-dependent reduction of NAD(+) in cell extracts of cyclopropanecarboxylate-grown cells was observed. When intermediates accumulated in vitro in the absence of NAD(+) were trapped as hydroxamic acids by reaction with hydroxylamine, cyclopropanecarboxohydroxamic acid and 3-hydroxybutyrohydroxamic acid were formed. Cyclopropanecarboxyl-coenzyme A (CoA), 3-hydroxybutyryl-CoA, and crotonyl-CoA were oxidized with NAD(+) in cell extracts, whereas methacrylyl-CoA and 3-hydroxyisobutyryl-CoA were not. When both CoA and ATP were added, organic acids corresponding to the former three CoA thioesters were also oxidized in vitro by NAD(+), while methacrylate, 3-hydroxyisobutyrate, and 2-hydroxybutyrate were not. Therefore, it was concluded that cyclopropanecarboxylate undergoes oxidative degradation through cyclopropanecarboxyl-CoA and 3-hydroxybutyryl-CoA. The enzymes catalyzing formation and ring opening of cyclopropanecarboxyl-CoA were shown to be inducible, while other enzymes involved in the degradation were constitutive.