Physiological metabolic topology analysis of Halomonas elongata DSM 2581^T in response to sodium chloride stress

Abstract

The halophilic bacterium Halomonas elongata DSM 2581 T generally adapts well to high level of salinity by biosynthesizing ectoine, which functions as an important compatible solute protecting the cell against external salinity environment.Halophilic bacteria have specific metabolic activities under high-salt conditions and are gradually applied in various industries. The present study focuses on investigating the physiological and metabolic mechanism of H. elongata DSM 2581 T driven by the external salinity environment. The physiological metabolic dynamics under salt stress were investigated to evaluate the effect of NaCl stress on the metabolism of H. elongata. The obtained results demonstrated that ectoine biosynthesis transited from a nongrowth-related process to a growth-related process when the NaCl concentration varied from 1% to 13% (w/v). The maximum biomass (X m = 41.37 g/L), and highest ectoine production (P m = 12.91 g/L) were achieved under 8% NaCl. Moreover, the maximum biomass (X m ) and the maximum specific growth rates (μ m ) showed a first rising and then declining trend with the increased NaCl stress. Furthermore, the transcriptome analysis of H. elongata under different NaCl concentrations demonstrated that both 8% and 13% NaCl conditions resulted in increased expressions of genes involved in the pentose phosphate pathway, Entner-Doudoroff pathway, flagellar assembly pathway, and ectoine metabolism, but negatively affected the tricarboxylic acid cycle and fatty acid metabolism. At last, the proposed possible adaptation mechanism under the optimum NaCl concentration in H. elongata was described.

Temporal dynamics of stress response in Halomonas elongata to NaCl shock: physiological, metabolomic, and transcriptomic insights

“…Under 5% NaCl shock, H. elongata exhibited high robustness, quickly restoring its growth rate and ultimately achieving the highest biomass. This finding is consistent with the previous study indicating a maximum specific growth rate under 6% NaCl condition [19]. When exposed to 8% NaCl, H. elongata required a longer recovery time for the cell growth, while the ectoine content rapidly increased after shock and reached the highest level.…”

“…When exposed to 8% NaCl, H. elongata required a longer recovery time for the cell growth, while the ectoine content rapidly increased after shock and reached the highest level. This finding is also consistent with previous research, where the highest ectoine production was observed under 8% NaCl condition [19]. Notably, the obtained maximum ectoine productivity (1450 ± 99 mg/L/h) in 8% NaCl shock was substantially higher than that in other halophiles and even exceeded its value (1130 ± 20 mg/L/h) under normal cultivation in 8% NaCl [19].…”

“…Moreover, the genes encoding chemotaxis and flagellar assembly are strongly upregulated under salt stress [13]. Our previous study also demonstrated the flexible adaptation of Halomonas elongata DSM 2581 T to varying salt concentrations [19], with the highest biomass and ectoine accumulation achieved at 8% NaCl, accompanied by enhanced ectoine biosynthesis and ED pathway compared to that under 1% NaCl condition [18]. Furthermore, potassium is also found to play essential roles in osmoregulation in H. elongata [20].…”

“…Salinity fluctuations present a daily challenge for microorganisms [27]. Halomonas elongata, a moderately halophilic bacterium with a broad NaCl tolerance range (1-16%) [13,19], serves as an exemplary model for studying the stress response to NaCl shock. This study investigated the stress response of H. elongata to NaCl shock by utilizing a multi-parameter online detection platform for continuous monitoring of physiological changes.…”

Improved salt tolerance of Synechococcus elongatus PCC 7942 by heterologous synthesis of compatible solute ectoine

“…Moreover, under 100 mM NaCl, the yield of ectoine was significantly increased, reaching 98.9 mg/l. It has also been reported that ectoine production increased with the concentration of NaCl in the environment ( Ning et al, 2016 ; Yu et al, 2022 ), and this phenomenon also occurred in the synthesis of glucosylglycerol and sucrose ( Song et al, 2016 ; Cui et al, 2021 ). With the further increase of salt concentration, the yield of ectoine decreased compared with under 100 mM NaCl, most probably due to the worse growth caused by salt stress.…”