Figure 3.

Graphical representation of potential metabolic activities of acidophilic Sideroxydans strains. The figure represents the pool of metabolic pathways that were reconstructed from the metagenomic sequence data of contigs assigned to strains of the genus Sideroxydans. It therefore does not express the co-occurrence of various pathways within the same strain. Biochemical reactions do not reflect real stoichiometry with the exception of cases were it was judged to be of relevance. Question marks indicate that it is unknown which sulfur compound is oxidized via the Sox enzyme system. Based on its pKa (3.86) lactate is depicted in its acid form outside the cell, though the narrow difference to the external pH (3.5) means that only a small fraction of molecules will be protonated. Please also note in this context that, no lactate was added to the culture medium. Dotted arrows indicate that no details are provided on the multiple enzymes involved in the pathway while dashed lines indicate the potential path of a volatile compound (i.e., H₂). For reasons of clarity no details are provided on the tricarboxylic acid (TCA) cycle. Arrows deviating from the the TCA cycle indicate its relevance as a central carbon metabolic pathway, though this line of metabolic function was not further investigated in this study. Carbon dioxide appears to be reduced to 3-phosphoglycerate via the Calvin-Benson-Bassham cycle indicated by its key enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Names for the nitrate transporter and nitrate and nitrite reductases are not indicated due to contradicting nomenclature in the databases. FHL, formate hydrogenlyase; AC III, alternative complex III; ETF, electron transfer flavoprotein oxidoreductase; SDH, succinate dehydrogenase; SQR, sulfide quinone oxidoreductase; CA, carbonic anhydrase; NADH dh, NADH dehydrogenase; Phn, phosphonate uptake system. Enzymes involved in metabolic pathways are abbreviated by their acronyms. For details see Supplementary Table 4.