Halomonas alkaliphila ZB109: growth characterization and optimization of fermentation conditions for ectoine accumulation

Abstract:

[Background] Zabuye Salt Lake with high concentrations of CO₃^2-, HCO₃^-, and Na⁺ may harbor Halomonas strains with potential applications. [Objective] To screen the Halomonas strains capable of accumulating the compatible solute ectoine, analyze the factors influencing ectoine accumulation, and optimize the fermentation conditions for ectoine accumulation in these strains. [Methods] The Horikoshi-I medium was used to isolate the strains with salinity tolerance and capable of efficiently accumulating ectoine from the water samples collected from Zabuye Salt Lake. The strains were then characterized in terms of biochemical properties and taxonomic status. Single factor tests, Plackett-Burman design, Box-Behnken design, and HPLC were employed to analyze the key factors influencing the intracellular ectoine accumulation and optimize the fermentation conditions. [Results] A total of 10 strains belonging to 5 species of Halomonas were isolated from Zabuye Salt Lake, and the dominant species was H. alkaliphila (4 strains, 40%). H. alkaliphila ZB109 presented good growth within the salt range of 0.5-2.5 mol/L and pH 8.0-10.0, with the initial ectoine accumulation of 303.62 mg/L. The colonies of ZB109 were round, yellow, with smooth edge. ZB109 was a Gram-negative bacterial strain with short rod cells growing cilia around. NaCl, Mg²⁺, and the concentration of sodium l-glutamate (substrate) were the key factors influencing the accumulation of ectoine by strain ZB109. After the fermentation conditions were optimized by response surface methodology, strain ZB109 was able to accumulate ectoine up to 696.313 mg/L (48 h) in a single batch of shake flask fermentation. [Conclusion] Strain ZB109 with both salt and alkali tolerance demonstrates stronger potential in the accumulation of ectoine than other wild-type strains of Halomonas. It serves as an elite strain for the large-scale production of ectoine by fermentation.