Pulsed electric field promotes the growth metabolism of aerobic denitrifying bacteria Pseudomonas putida W207-14 by improving cell membrane permeability

The purpose of this study was to explore the stimulation mechanism of low pulsed electric field (PEF) strength treatment to promote the growth metabolism of aerobic denitrifying bacteria Pseudomonas putida W207-14. The results indicated that compared with the control group, the strain W207-14 treated with PEF entered the logarithmic growth phase 5 h earlier, the growth time to reached the maximum cell optical density at 600 nm (OD600) of 1.935 ± 0.04 was only 24 h, which shortened by half. With the reduction of growth time, the metabolic rate of the strain increased significantly, in which the removal efficiency of COD, NO3--N and TN was 97.67 ± 1.12%, 90.34 ± 0.73% and 90.13 ± 0.10% in 24 h, respectively. The maximum nitrate removal rate increased from 3.49 mg/L/h to 7.53 mg/L/h. A large number of cells with simultaneous cell membrane damage and high physiological activity were observed by flow cytometry (FCM) in combination with fluorescence staining analysis, which confirmed the reversible electroporation on the cell membrane of strain W207-14 treated with PEF. Transcriptomic analysis indicated that PEF activated the highly significant differential expression of membrane porin (opdB, opdC, and oprB) and cytochrome oxidoreductase related genes (ccoP, ccoN, cioA and cioB) on the cell membrane, which promoted the transport of nutrients through the cell membrane and electron transfer during aerobic respiration and provided an explanation for the possible mechanism of PEF promoting the growth metabolism of strain W207-14 at the micro level. These results lay a foundation for the practical application of PEF enhanced aerobic denitrification technology.