C[O.sub.2]-responsive expression and gene organization of three ribulose-1,5-bisphosphate carboxylase/oxygenase enzymes and carboxysomes in Hydrogenovibrio marinus strain MH-110

Hydrogenovibrio marinus strain MH-110, an obligately lithoautotrophic hydrogen-oxidizing bacterium, fixes C[O.sub.2] by the Calvin-Benson-Bassham cycle. Strain MH-110 possesses three different sets of genes for Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO): CbbLS-1 and CbbLS-2, which belong to form I ([L.sub.8][S.sub.8]), and CbbM, which belongs to form II ([L.sub.x]). In this paper, we report that the genes for CbbLS-1 (cbbLS-1) and CbbM (cbbM) are both followed by the cbbQO genes and preceded by the cbbR genes encoding LysR-type regulators. In contrast, the gene for CbbLS-2 (cbbLS-2) is followed by genes encoding carboxysome shell peptides. We also characterized the three RubisCOs in vivo by examining their expression profiles in environments with different C[O.sub.2] availabilities. Immunoblot analyses revealed that when strain MH-110 was cultivated in 15% C[O.sub.2], only the form II RubisCO, CbbM, was expressed. When strain MH-110 was cultivated in 2% C[O.sub.2], CbbLS-1 was expressed in addition to CbbM. In the 0.15% C[O.sub.2] culture, the expression of CbbM decreased and that of CbbLS-1 disappeared, and CbbLS-2 was expressed. In the atmospheric C[O.sub.2] concentration of approximately 0.03%, all three RubisCOs were expressed. Transcriptional analyses of mRNA by reverse transcription-PCR showed that the regulation was at the transcriptional level. Electron microscopic observation of MH-110 cells revealed the formation of carboxysomes in the 0.15% C[O.sub.2] concentration. The results obtained here indicate that strain MH-110 adapts well to various C[O.sub.2] concentrations by using different types of RubisCO enzymes.