A salt tolerant Enterobacter cloacae mutant for bioaugmentation of petroleum- and salt-contaminated soil

A NaCl-tolerant Enterobacter cloacae variant (MU-1) was obtained by mutagenesis using atmospheric pressure glow discharge (APGD) plasmas. The variant exhibited regular growth behavior in slurry cultivation and reached a cell density of 5.72 × 108 and 6.44 × 108 colony-forming units (CFU/mL) in the presence and absence of 7.5% NaCl, respectively, when crude oil was used as the sole carbon source (crude oil/soil = 1.5%). The total petroleum hydrocarbon (TPH) degradation percentage was 7.94% with mutant MU-1 in the presence of 7.5% NaCl whereas that of the wild-type strain was 3.17%. When cultivated in saline medium, MU-1 showed a slight change in membrane permeability but significant increases in both the K+ concentration inside the cell membrane (from 234.24 to 1422.88 ppm/g dry cell weight in the first 2 h) and the exopolysaccharide (EPS) level outside the membrane (from 1350 to 1825 mg/g dry cell weight). The rapid increase in K+ inside the cell and the simultaneous accumulation of EPS outside the cell may be responsible for maintaining the osmotic balance during saline cultivation, and this could facilitate the microbial growth and TPH degradation of MU-1.