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The c-type cytochrome (c-Cyts) is a key protein in microbial oxidation of Fe(II). However, the reaction process and influencing factors of ligand-bound Fe(II) with c-Cyts under acidic conditions remain unclear. In this study, Fe(II)-EDTA and a model c-type cytochrome (c-Cyts) were used to investigate the mechanism of microbial Fe(II) oxidation under acidic conditions with various environmental factors, including anoxic/oxic conditions, pH, and initial Fe(II)-EDTA concentration. A stopped-flow spectrophotometer was employed to study the reduction kinetics of c-Cyts, while the electrochemical properties of Fe(II) and the distribution of different Fe(II) species were characterized. Under anoxic conditions, the reduction rate of c-Cyts increased with increasing pH and Fe(II)-EDTA concentration. At 20μmol/L Fe(II)-EDTA, the apparent rate constants (kapp) were 0.841 and 6.802s-1 at pH 3.5 and pH 5.0, respectively. At pH 5.0, the kapp increased to 13.028s-1 when the initial Fe(II)-EDTA concentration increased to 80μmol/L. The increase in pH and Fe(II)-EDTA concentration enhanced the proportion of FeEDTA2- and intensified the redox peaks of Fe(II), indicating greater Fe(II) reactivity and thus a faster c-Cyts reduction rate. Compared to anoxic conditions, c-Cyts reduction was inhibited under oxic conditions. This inhibitory effect of oxygen decreased as the pH increased. At pH 3.5 and 4.0, c-Cyts reduction was completely inhibited. At pH 4.5, the kapp decreased from 5.402s-1 (anoxic) to 1.658s-1 (oxic); and at pH 5.0, the kapp slightly decreased from 6.802s-1 (anoxic) to 6.454s-1 (oxic). This is attributed to the slower reaction between Fe(II)-EDTA and c-Cyts at lower pH, whereas the competing reaction of Fe(II)-EDTA with oxygen is favored, producing reactive oxygen species that further accelerate the reoxidation of reduced c-Cyts. This study elucidates the critical mechanisms of the reaction between Fe(II)-ligand and c-Cyts, providing deeper molecular-level insight into the microbial Fe(II) oxidation process.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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