Fig 1.
Growth of D. carbinolicus on various alcohols as electron donors in batch cultures.
A shaded interval in (B) indicates the first 160 hours of the batch culture experiments (A). Methanol A represents the methanol batch culture inoculated with ethanol-grown cells, while methanol B indicates a second-generation culture inoculated with methanol A.
Fig 2.
Time evolution of concentrations and sulfur isotope compositions of metabolites during the batch culture containing methanol as a sole electron donor (A-C) and ethanol and methanol as mixed substrates (D-E).
Table 1.
Concentrations and sulfur isotope compositions of sulfur metabolites after the complete consumption of alcohols by D. carbinolicus.
Table 2.
Comparison of growth parameters and sulfur isotope fractionations in D. carbinolicus batch cultures containing methanol and/or ethanol as electron donors.
Fig 3.
(A) Variations in specific respiration rate and sulfur isotope effect during sulfate reduction coupled to methanol or ethanol oxidation, reported in this study and previous literature [18, 48, 50, 51]. For the comparison with prior work, the respiration rate normalized by optical density is converted to the approximate cell-specific sulfate reduction rate (csSRR) according to the conversion factor for optical density to total cell volume (A660 of 1.0 as 1.49 μl/ml [52]) and the average cell volume of 1.68 μm3 [3]. (B) Pattern of the sulfur isotope fractionation and the free energy change (ΔG) for APS reduction, predicted based on the model originally proposed by Wing and Halevy [21] and modified by Sim et al. [45]. Sulfur isotope fractionation and free energy change are calculated as a function of both csSRR and reduction potential of the electron-donating half reaction. The former varies from 1 fmol/cell/day to 100 fmol/cell/day and the latter from -140 mV to -70 mV. All calculations are made using the constant sulfate and sulfide concentrations of 15 mM and 5 mM, respectively, which approximates when the reaction is half completed.
Fig 4.
Phylogenetic tree of the selected sulfate-reducing bacteria based on 16S rRNA sequence (A) and of the genes encoding homologous proteins to methanol-oxidizing alcohol dehydrogenase (B) and methanol methyltransferase (C) of D. kuznetsovii [9]. This analysis involves 52 species of sulfate-reducing bacteria that have their genome sequenced and deposited in NCBI database and have been tested for methanol metabolism [3–8, 12, 49, 55–88]. The trees were constructed using MEGA X software with the neighbor-joining method. Numbers before each branch point represents the percentage of bootstrap resampling based on 2,000 trees. Bootstrap values below 50% are not shown. D. carbinolicus examined in this study is highlighted in a blue box.
Table 3.
Presence of methanol dissimilating enzyme homologs in SRMs capable of methanol oxidation and their growth properties.