Identification and characterization of ectoine-producing bacteria isolated from Can Gio mangrove soil in Vietnam

Abstract

Purpose: The aim of this study was to characterize high ectoine-producing bacteria obtained from Can Gio mangrove soil samples in Vietnam. Methods: Ectoine-producing bacteria were isolated from mangrove soil samples. The selected strains were identified using 16S rDNA sequence analysis, and their biochemical characteristics were also examined. The ability to produce ectoine at different NaCl concentrations and the effect of osmotic downshock solution on ectoine’s release rates and survival rates for the selected bacterial strains were investigated. Results: Among more than 200 bacterial colonies isolated from soil samples, two strains exhibiting highest ectoine production (strains D227 and D228) were chosen for further studies. Both strains D227 and D228 were identified as Halomonas spp. and were closely related to Halomonas organivorans, sharing 99.4% 16S rDNA sequence similarity. At 6% (w/v) NaCl concentration, strains D227 and D228 presented the highest cell dry weight (CDW) of 3.85 and 3.55 g/l, respectively. At 18% NaCl concentration, maximum total ectoine (ectoine and hydroxyectoine) production of 16.4 and 18.1 wt% was achieved by strains D227 and D228, respectively. After 30 min of incubation in downshock solution containing 5% NaCl, high bacterial survival rates of 96% and 98%, and ectoines release rates of 61% and 76% were obtained by strains D227 and D228, respectively. Conclusions: The accumulation and secretion of ectoine appear to be a typical adaptation strategy of some bacteria to survive under the changing saline conditions of mangrove ecosystem. To the best of our knowledge, this is the first report on ectoine production by halophilic bacteria isolated from mangrove soil. High ectoine-producing bacteria can be found in mangrove forest.