Nickel requirement for active hydrogenase formation in Alcaligenes eutrophus

Abstract

The Ni-dependent chemolithoautotrophic growth of A. eutrophus is apparently due to a requirement of Ni for active hydrogenase formation. Cells grown heterotrophically with fructose and glycerol revealed a specific activity of soluble and membrane-bound hydrogenase which was severalfold higher than the normal autotrophic level. The omission of Ni from the medium did not affect heterotrophic growth, but the soluble hydrogenase activity was reduced significantly. In the presence of EDTA, almost no hydrogenase activity was detected. The addition of Ni allowed active hydrogenase formation even when EDTA was present. When chloramphenicol was added simultaneously with Ni to an EDTA-containing medium, almost no hydrogenase activity was found. This indicates that Ni ions are involved in a process which requires protein synthesis, and not the direct reactivation of a preformed inactive protein. The formation of the membrane-bound hydrogenase also appeared to be Ni dependent. Autotrophic CO2 assimilation did not specifically require Ni ions, since formate was used in the presence of EDTA and the activity of ribulosebisphosphate carboxylase was not affected under these conditions.