Unusual ribulose-1,5-bisphosphate carboxylase/oxygenase genes from a marine manganese-oxidizing bacterium

The Gram-negative bacterium strain S185-9A1 is a novel marine α-proteobacterium that oxidizes manganese(II) to manganese(IV). Initial DNA hybridization screening showed that S185-9A1 possesses a gene similar to cbbL, the gene coding for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO; EC 4.1.1.39). However, no RubisCO enzyme activity was found in cultures of S185-9A1. Genes coding for both large (cbbL) and small (cbbS) subunits of a RubisCO enzyme were identified, isolated and sequenced. When these genes were introduced into an Escherichia coil host strain, ribulose-1,5-bisphosphate-dependent CO₂ fixation occurred under control of a lac promoter, indicating that the protein is functional in E. coil. Although their function is unknown, this is the first direct evidence for the presence of RubisCO genes in a manganese-oxidizing bacterium. Phylogenetic analysis of the RubisCO genes of strain S185-9A1 showed that they are divergent, but are more related to those from non-chlorophyte algal chloroplasts than are those from other bacteria. The fact that the RubisCO sequence of strain S185-9A1 is not closely related to any other published RubisCO sequence suggests that the protein may be valuable for studies of the function and evolution of the RubisCO enzyme as well as its activity in the environment.