Iron oxidation coupled with nitrate reduction affects the acetate-assimilating microbial community structure elucidated by stable isotope probing in flooded paddy soil

Fe(II) Oxidation Shaped Functional Genes and Bacteria Involved in Denitrification and Dissimilatory Nitrate Reduction to Ammonium from Different Paddy Soils

“…The complete nitrate reduction in the soil + NO 3 – treatment (Figure A) indicates that active nitrate-reducing bacteria have been enriched from LA and TS soils. Dechloromonas and Bdellovibrio were enriched from both soils under nitrate-reducing conditions (Figure ), which have been also detected in other paddy soils under nitrate-reducing and/or Fe­(II)-oxidizing conditions. , Dechloromonas was the functional genus carrying napAB , nirS , norBC , nosZ , and nirBD genes (Figure ), which implied that it could mediate the nitrate reduction and subsequent denitrification in the periplasm, as well as the NO 2 – -to-NH 4 + reduction in the cytoplasm. The genus Dechloromonas possesses a complete denitrification pathway with napA , nirS , norB , and nosZ genes, − and has been frequently detected in various soil environments. ,, Unlike Dechloromonas, Bdellovibrio was the functional genus harboring the narG gene that encodes the cytoplasmic membrane-bound nitrate reductase (11.2% ∼ 16.8%, Table S13).…”

“…With respect to N 2 O reduction, Pseudogulbenkiania was enriched as the dominant genus carrying the nosZ gene from both LA and TS soils, and the relative abundance of this gene was increased by Fe­(II) addition as well (Figure ). The Pseudogulbenkiania genus has been frequently detected in the nitrate-reducing Fe­(II) oxidation microcosms, which is associated with acetate assimilation and the reduction of NO 3 – , NO 2 – , and NO. ,,, However, the subsequent NO and N 2 O reductions were also inhibited during Fe­(II) oxidation, likely due to the inactivation of the reductases by cell encrustation.…”

“…Previous studies together with this study confirm that chemodenitrification mainly drives Fe­(II) oxidation once nitrite is produced by nitrate-reducing bacteria under heterotrophic conditions. It has been reported that the secondary minerals formed after nitrate-reducing Fe­(II) oxidation play a predominant role in carbon and nitrogen sequestration as well as heavy metal immobilization, e.g., arsenic, cadmium, and nickel. ,− The enriched nitrate-reducing bacteria, i.e., Dechloromonas, Pseudogulbenkiania, Azospira, and Pseudomonas, are widely distributed in the environments. ,, Given that these bacteria show high adaptability and activity during Fe­(II) oxidation, it deserves further investigation on whether they could be stimulated in situ or used as microbial agents to facilitate nitrate-reducing Fe­(II) oxidation and the formation of secondary minerals in an anoxic environment, resulting in promoted carbon/nitrogen sequestration and heavy metal remediation.…”

“…Dechloromonas and Bdellovibrio were enriched from both soils under nitrate-reducing conditions (Figure 3), which have been also detected in other paddy soils under nitrate-reducing and/or Fe(II)-oxidizing conditions. 26,55 Dechloromonas was the functional genus carrying napAB, nirS, norBC, nosZ, and nirBD genes (Figure 5), which implied that it could mediate the nitrate reduction and subsequent denitrification in the periplasm, as well as the NO 2 − -to-NH 4 + reduction in the cytoplasm. The genus Dechloromonas possesses a complete denitrification pathway with napA, nirS, norB, and nosZ genes, 56−58 and has been frequently detected in various soil environments.…”

“…The Dechloromonas genus has been reported as nitrate-reducing Fe(II)-oxidizing bacteria previously, 77 and is prevalent in groundwater and soils when Fe(II), nitrate, and organic substrates coexist. 26,55,78 Many members of the Thauera genus possess a complete set of denitrification genes. 79 The Rhodocyclaceae family, phylogenetically affiliated with β-proteobacteria, consists of 18 genera, including Dechloromonas, Azospira, Azoarcus, and Thauera, 80 which were the dominant genera enriched in the soil + Fe(II) + NO 3 − treatment (Figure 3).…”