Role of electron donor in CO2 fixation of chemoautotrophic bacteria and its preconditions: Verification in Alcaligenes hydrogenophilus.

Alcaligenes hydrogenophilus was used to verify the role of the electron donor and acceptor in apparent CO2 fixation of chemoautotrophic bacteria. The response mechanisms underlying the apparent CO2 fixation characteristics with different concentrations of electron donor and acceptor were elucidated by analyzing the transcription characteristics of the cbbL gene, cytoskeleton synthesis efficiency and extracellular free organic carbon concentration. The results showed that the apparent CO2 fixation efficiency of A. hydrogenophilus was significantly influenced by the electron donor (H2), and the degree of electron donor oxidization was responsible for the variation in apparent CO2 fixation efficiency. Furthermore, transcription efficiency of the cbbL gene at low electron donor concentration was lower than that at high electron donor concentration, but excessive electron donor concentrations did not further increase cbbL gene transcription efficiency significantly. High oxygen concentration was not advantageous to cbbL gene transcription efficiency in A. hydrogenophilus, but could improve cell growth rate (protein synthesis rate) and apparent CO2 fixation efficiency, implying that cytoskeleton synthesis efficiency is another important factor determining apparent CO2 fixation efficiency and its contribution maybe greater than that of cbbL transcription. The results also indicated that high apparent CO2 fixation efficiency required the matching of electron donor and acceptor.