Efficiency Determination and Mechanism Investigation of Autotrophic Denitrification Strain F1 to Promote Low-Carbon Development

Shewanella sp. strain F1, isolated from a lab-scale Fe(II)−dependent anaerobic denitrifying reactor, could reduce nitrate by oxidizing Fe(II). Its nitrate reduction rate and Fe(II) oxidation rate were 0.48 mg/(L·h) and 5.05 mg/(L·h) at OD₆₀₀ of 0.4786 with a five-fold diluent. Shewanella sp. was popular in Fe(III) reduction. Fewer studies about its ability for Fe(II) oxidation are available. The low pH was determined to be the switch for Shewanella sp. strain F1 to perform Fe(III) reduction or Fe(II) oxidation. Even under a low pH, the produced Fe(III) precipitated around cells from iron encrustation. By observation of the morphologies of strain F1, two corresponding microbial mechanisms were proposed. One was named Cyc 2−based Fe(II)-dependent denitrification, in which Fe(II) was oxidized by Cyc 2 in the outer cell membrane, and the produced Fe(III) precipitated on the cell wall surface to form tiled iron encrustation. The other was named Cyc 1−based Fe(II)−dependent denitrification, in which Fe(II) was oxidized on the existing iron precipitation on the cell wall surface to form towery iron encrustation, and the electron was transported to Cyc 1 in the periplasm. The efficiency determination and mechanism investigation of strain F1 will promote the development of autotrophic denitrification technology and meet the requirement of a low−carbon policy.