Ectoine and 5-hydroxyectoine accumulation in the halophile Virgibacillus halodenitrificans PDB-F2 in response to salt stress.
The moderately halophilic bacterium Virgibacillus halodenitrificans PDB-F2 copes with salinity by synthesizing or taking up compatible solutes. The main compatible solutes in this strain were ectoine and hydroxyectoine, as determined by (1)H nuclear magnetic resonance spectroscopy ((1)H-NMR). A high-performance liquid chromatography (HPLC) analysis showed that ectoine was the major solute that was synthesized in response to elevated salinity, while hydroxyectoine was a minor solute. However, the hydroxyectoine/ectoine ratio increased from 0.04 at 3 % NaCl to 0.45 at 15 % NaCl in the late exponential growth phase. A cluster of ectoine biosynthesis genes was identified, including three genes in the order of ectA, ectB, and ectC. The hydroxyectoine biosynthesis gene ectD was not part of the ectABC gene cluster. Reverse transcription-quantitative polymerase chain reactions (RT-qPCR) showed that the expression of the ect genes was salinity dependent. The expression of ectABC reached a maximum at 12 % NaCl, while ectD expression increased up to 15 % NaCl. Ectoine and hydroxyectoine production was growth phase dependent. The hydroxyectoine/ectoine ratio increased from 0.018 in the early exponential phase to 0.11 in the stationary phase at 5 % NaCl. Hydroxyectoine biosynthesis started much later than ectoine biosynthesis after osmotic shock, and the temporal expression of the ect genes differed under these conditions, with the ectABC genes being expressed first, followed by ectD gene. Increased culture salinity triggered ectoine or hydroxyectoine uptake when they were added to the medium. Hydroxyectoine was accumulated preferentially when both ectoine and hydroxyectoine were provided exogenously.
State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, State Key Laboratory of Biological Reactor Engineering, School of Resource and Environmental Engineering, East China University of Science and Technology, Shanghai, 200237, People's Republic of China.
Ping
P
Tao
State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, State Key Laboratory of Biological Reactor Engineering, School of Resource and Environmental Engineering, East China University of Science and Technology, Shanghai, 200237, People's Republic of China. huili@ecust.edu.cn.
Hui
H
Li
Center for Environmental Health Research, South China Institute of Environmental Sciences, Guangzhou, 510535, People's Republic of China.
Yunjiang
Y
Yu
School of Biological Sciences, Swire Institute of Marine Science, The University of Hong Kong, Pokfulam Road, Hong Kong, SAR, People's Republic of China.
Jidong
J
Gu
State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, State Key Laboratory of Biological Reactor Engineering, School of Resource and Environmental Engineering, East China University of Science and Technology, Shanghai, 200237, People's Republic of China. ydliu@ecust.edu.cn.
Yongdi
Y
Liu
D000599:Amino Acids, Diamino / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D009997:Osmotic Pressure / Q000502:physiology*; D054712:Salinity; D055049:Salt Tolerance / Q000235:genetics / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D013312:Stress, Physiological / Q000502:physiology; D058679:Virgibacillus / Q000378:metabolism*
D000599:Amino Acids, Diamino; C121557:hydroxyectoine; D012965:Sodium Chloride; C045628:ectoine
Compatible solutes; Ectoine; Halophilic bacteria; Hydroxyectoine; ectABC; ectD