Salt tolerance mechanism and betaine transport genes of a petroleum-degrading strain HX-2

Abstract:

[Background] It is challenging to remediate water and soil contaminated by petroleum hydrocarbons under high salt conditions. Therefore, it is important to explore the salt tolerance of petroleum hydrocarbon-degrading strains. [Objective] Salt tolerance and relevant genes of petroleum-degrading strain HX-2 were studied. [Methods] The hydrocarbon-degrading strain HX-2 under different petroleum amount and high salinity conditions was analyzed by GC. The intracellular ion content was analyzed by conductivity meter and atomic absorption spectroscopy. The effects of exogenous betaine on extracellular polysaccharide and petroleum degradation in high salinity soils were compared before and after adding betaine; finally, the related genes for salt tolerance were analyzed by qPCR. [Results] The petroleum-degrading strain Rhodococcus sp. HX-2 degraded 10 000?100 000 mg/L of petroleum. After three days of cultivation, the degradation rate of petroleum reached more than 70%, and it degraded petroleum in the presence of 1%?10% NaCl. At 6% salt concentration, the degradation rate was still 43.8%. Studies on the salt tolerance mechanism showed that there was no significant difference in intracellular cation concentration with the change of salt concentration. Accumulating betaine compatible substances and promoting the synthesis of extracellular polysaccharide were the salt tolerance mechanisms of petroleum hydrocarbon-degrading strain HX-2. Meanwhile, the results of scanning electron microscopy showed that the addition of exogenous betaine could improve the salt tolerance of the strain by stimulating the synthesis of EPS. Four betaine transporter genes H0, H1, H3, H5 and a betaine synthesis related gene BetB were obtained from HX-2 strain. The analysis of gene transcription showed that NaCl and betaine induced the expression of H0, H1, H3 and H5. When betaine coexisted with NaCl, the level of gene transcription reached the maximum. [Conclusion] Rhodococcus sp. HX-2 has potential application in remediation of hydrocarbon pollutants in saline environment.