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

Abstract

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.

Ectoine and Hydroxyectoine from Halophilic Bacteria Isolated from Traditional Solar Saltern at Pejarakan Village, Buleleng Regency, Bali

“…Three strains of our bacteria, i.e., K10 (3), K10 (5), and K10 (21), were able to produce 0.263, 0.201, and 0.302 g/L ectoine, respectively after incubated for 28 hours in MM63 media containing 12% w/v NaCl. The bacteria were also reported able to release 61% and 76% of ectoine, respectively for strains D227 and D228 after the osmotic downshock process for 30 min in a solution containing 5% NaCl ( Van-Thuoc et al 2019). Interestingly, two bacteria in our study, i.e., K10 (5) and K10 (21) were able to release 85.5% and 91.9% of ectoine after the osmotic downshock using distilled water containing 1% w/v NaCl for 30 minutes.…”

“…Recently, studies on the explorations of ectoine and hydroxyectoine-producing bacteria have been reported. Van-Thuoc et al (2019) have investigated the ectoine-producing bacteria from Can Gio mangrove soil samples in Vietnam. The results showed that two strains among more than 200 isolates obtained, i.e., D227 and D228, could produce ectoine with levels of 0.11 and 0.12 g/L, respectively, after incubated for 30 hours in meat peptone agar (MPA) containing 15% NaCl.…”

“…Ectoine and hydroxyectoine were extracted following Bligh and Dyer procedure ( Van-Thuoc et al 2019). The cell pellets were dried at 70°C for 1 hour, then extracted with 350 µl of methanol/chloroform/ water (10:5:4, vol/vol/vol).…”

“…Ectoine and hydroxyectoine are secondary metabolites produced by halophilic microorganisms as a protection strategy of the cell against high salt levels in their habitat. Indonesia has various types of ecosystems with high salinity, including salt ponds (Wei et al 2011), mangrove muds ( Van-Thuoc et al 2019), and shallow and deep-sea sediments…”

The saltern-derived Paludifilum halophilum DSM 102817T is a new high-yield ectoines producer in minimal medium and under salt stress conditions

“…In the optimized SW-15 medium, the total ectoines content produced by P. halophilum increased with growth and reached the maximum value of about 119 mg g −1 at the end of the exponential growth phase. This content generated by the strain, still slightly lower to that of other efficient producers such as H. organivorans (165 mg g −1 ) (Van Thuoc et al 2019) or the commercial ectoine producers H. elongata (155 mg g −1 ) (Sauer and Galinski 1998), could be further improved in controlled bioreactor fermentations. During the exponential growth phase of P. halophilum, a mixture of ectoine and 5-hydroxyectoine, with ectoine dominating the ectoine/5-hydroxyectoine solute pool was observed (Fig.…”