Enhancement of bacterial salt tolerance by a newly identified superoxide dismutase from archaea Haloferax sp. D1227

Abstract:

[Background] Heterologous expression of many superoxide dismutases (SODs) from bacteria, yeast or plants have been reported to improve the salt tolerance of the host, but few from archaea. In particular, no SODs from archaea has been expressed in bacteria to improve their salt tolerance. [Objective] We are aiming to mine putative SODs encoding genes in archaea Haloferax sp. D1227, and to identify its biochemical function. It is also our intention to see possible enhancement of salt tolerance in para-nitrophenol utilizer Burkholderia sp. SJ98, by introducing the newly identified SOD. [Methods] The putative SOD encoding gene from strain D1227 was mined by bioinformatics analysis before its heterologous expression in E. coli BL21(DE3) and strain SJ98, which was further purified through AKTA purifier system. The specific activity of cell extracts and purified enzyme were measured by a spectrophotometry. Cells of strain SJ98 with the SOD gene and with vector only were cultured in M9 medium (with 0 and 500 mmol/L NaCl) with glucose or PNP as carbon source, respectively. Subsequently, the growth and degradation of these strains were detected by automatic growth curve analyzer and high-performance liquid chromatography. [Results] A putative SOD encoding gene from Haloferax sp. D1227 was found and designated sodA. SodAD1227 heterologous expressed in both E. coli BL21(DE3) and strain SJ98 exhibited SOD activity (with specific activities of 21.07±0.02 U/mg and 84.56±0.16 U/mg respectively in cell extracts). The specific activity of purified protein from E. coli was 179.46±3.43 U/mg. Strain SJ98[pBBR-sodA] grew well in M9 containing 500 mmol/L NaCl with glucose as carbon source, while strain SJ98[pBBR1MCS-2] almost lost its growth ability. When para-nitrophenot (PNP) was used as carbon source, strain SJ98[pBBR-sodA] still had a normal growth with a proper PNP degradation ability, while the growth and degradation ability of strain SJ98[pBBR1MCS-2] was almost lost. The structural analysis of SodAD1227 simulated by Phyre2 showed that SodAD1227 has the typical structural characteristics of the Fe/Mn-SOD family. [Conclusion] This study provides a potential feasibility for the use of archaeal SODs in transforming bacteria to adapt to the degradation of organic pollutants in high salinity environment.