Abstract
Chlorobium tepidum can grow with N2 as the sole nitrogen source. The whole genome sequence of C. tepidum contains four putative Fd genes and Seo et. al. purified three Fds, each binding two [4Fe-4S] clusters. The genome contains one more Fd gene, which has a putative sequence motif for binding of [2Fe-2S] cluster, and is located on the downstream of nif operon that encode the structural genes of nitrogenase. In this study, we characterized the transcription of Fd genes in C. tepidum and found the [2Fe-2S] type Fd gene was expressed only under combined-nitrogen depleted conditions as were several nitrogenase genes. The expression of other [4Fe-4S] Fd genes were not significantly affected by nitrogen source. The [2Fe-2S] type Fd gene was overexpressed in Escherichia coli, and UV-visible absorption spectrum of the purified Fd was similar to those of Azotobacter vinelandii and Clostridium pasteurianum [2Fe-2S] Fds.
