The characteristics of carbon fixation of Halothiobacillus neapolitanus DSM 15147 with different concentrations of Na2S2O3.5H(2)O as reduced sulfur were investigated. Moreover, the mechanisms underlying the carbon fixation characteristics in response to different Na2S2O3.5H(2)O concentrations were clarified from the energy supply perspectives and the cbb gene transcription characteristics. The results showed that the carbon fixation efficiency of H. neapolitanus was influenced by the Na2S2O3.5H(2)O concentration, and the Na2S2O3.5H(2)O oxidization amount and energy- releasing efficiency per unit of Na2S2O3.5H(2)O were important reasons for the variation of carbon fixation efficiency at different Na2S2O3.5H(2)O concentrations. Moreover, the cbb gene transcription efficiency and transcription pattern were also influenced by the Na2S2O3.5H(2)O concentration, and when the Na2S2O3.5H(2)O concentration was too low or too high, it was not conducive to the cbb gene transcription process, thus resulting in the relatively low carbon fixation efficiency. Furthermore, low Na2S2O3.5H(2)O concentration was not beneficial to the cytoskeleton synthesis due to the insufficient energy supply and further resulted in the accumulation of extracellular free organic matters, which might induce a feedback inhibitory effect on the CO2 assimilation process by influencing the cbb gene transcription efficiency. (C) 2017 Elsevier B. V. All rights reserved.