Distribution and correlation of iron oxidizers and carbon-fixing microbial communities in natural wetlands

Most microaerophilic Fe(II)-oxidizing bacteria (mFeOB) belonging to the family Gallionellaceae are autotrophic microorganisms that can use inorganic carbon to drive carbon sequestration in wetlands. However, the relationship between microorganisms involved in Fe and C cycling is not well understood. Here, soil samples were collected from different wetlands to explore the distribution and correlation of Gallionella-related mFeOB and carbon-fixing microorganisms containing cbbL and cbbM genes. A significant positive correlation was found between the abundances of mFeOB and the cbbL gene, as well as a highly significant positive correlation between the abundances of mFeOB and the cbbM gene, indicating the distribution of mFeOB in co-occurrence with carbon-fixing microorganisms in wetlands. The mFeOB were mainly dominated by Sideroxydans lithotrophicus ES-1 and Gallionella capsiferriformans ES-2 in all wetland soils. The structures of the carbon-fixing microbial communities were similar in these wetlands, mainly consisting of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The extractable Fe(II) concentrations affected the community composition of mFeOB, resulting in a significant difference in the relative abundances of the dominant FeOB. The main factors affecting cbbL-related microbial communities were dissolved inorganic carbon and oxygen, soil redox potential, and sodium acetate-extracted Fe(II). The composition of cbbM-related microbial communities was mainly affected by acetate-extracted Fe(II) and soil redox potential. In addition, the positive correlation between these functional microorganisms suggests that they play a synergistic role in Fe(II) oxidation and carbon fixation in wetland soil ecosystems. Our results suggest a cryptic relationship between mFeOB and carbon-fixing microorganisms in wetlands and that the microbial community structure can be effectively altered by regulating their physicochemical properties, thus affecting the capacity of carbon sequestration.