Archaeal superoxide dismutase enhances bacterial degradation of nitrophenols under salt stress

Abstract:

[Background] Burkholderia sp. SJ98 utilizes para-nitrophenol or 2-chloro-4-nitrophenol as the sole carbon and energy source for its growth. The superoxide dismutase SodA from Haloferax sp. D1227 endows strain SJ98 with the ability to degrade para-nitrophenol with 500 mmol/L NaCl. However, it is unknown whether strain SJ98 containing sodA can degrade para-nitrophenol derivatives under conditions with high salt concentration. [Objective] We are aiming to study the salt tolerance of strain SJ98, and the degradation of para-nitrophenol and 2-chloro-4-nitrophenol by strain SJ98 containing sodA under normal and high salt concentrations. We also hope to detect the transcriptions of pnpA and the activities of the nitrophenols monooxygenase in the recombinants of strain SJ98. [Methods] Strain SJ98 and its recombinants were cultured in minimal medium (containing 400 to 800 mmol/L NaCl) or M9 medium (containing 0 and 500 mmol/L NaCl, respectively) supplemented with glucose, para-nitrophenol or 2-chloro-4-nitrophenol, respectively. The strains growth and substrates degradation were detected by UV spectrophotometer and high-performance liquid chromatography, respectively. The transcriptions of pnpA (nitrophenol monooxygenases encoding gene) induced by two nitrophenols were detected by quantitative real-time PCR. The activities of nitrophenols monooxygenase in the crude enzyme solutions were detected by UV spectrophotometer using two above substrates. [Results] The NaCl tolerance concentration of strain SJ98 was 600 mmol/L with glucose as the carbon source. The growth and para-nitrophenol degradation by strain SJ98[pCM-pnpR-PpnpA-sodA-rfp] were much better than those by the wild-type strain. With 500 mmol/L NaCl, strain SJ98[pBBR-sodA] still maintained the ability of degrading and growing on 2-chloro-4-nitrophenol, while strain SJ98[pBBR1MCS-2] completely lost these abilities; the activities of the nitrophenols monooxygenase against two above substrates in the crude enzyme solutions of strain SJ98[pBBR-sodA] were both about 1/3 of those in the wild strain. When two nitrophenols were used as inducers, the transcriptions of pnpA in strain SJ98[pBBR-sodA] were about 17–25 times higher than those in the wild-type strain, regardless of the presence of NaCl. However, when 500 mmol/L NaCl was added, the transcriptions of pnpA were partially inhibited. [Conclusion] This study provides a potential possibility for the application of superoxide dismutase from archaea to improve the ability of nitroaromatics degradation under normal and high salt concentrations by bacteria.