To investigate the impact of high salt stress on the metabolic pathways and regulatory mecha-nisms involved in synthesizing hydroxyectoine(5-HE)in Virgibacillus salexigens,cultures were supple-mented with 1.5 and 2.5 mol/L NaCl as control and experimental groups,respectively.High-perform-ance liquid chromatography(HPLC)was used to detect the difference in the amount of 5-HE synthesis.Transcriptomic and metabolomic analyses identified differential genes and metabolites under varying salt concentrations.Key differential gene expressions related to 5-HE synthesis were validated using qRT-PCR.Results showed that 5-HE synthesis reached 121.9 mg/L at 2.5 mol/L NaCl.Transcriptomic anal-ysis identified 652 differentially expressed genes across 348 KEGG pathways,with 210 upregulated and 442 downregulated,primarily enriched in pathways such as purine metabolism,amino acid biosynthesis,sulfur metabolism,and biotin metabolism.Validation of 13 genes,including lysC,asd,ectA,ectB,ectC,ectD,thrB,thrC,ilvA,ilvE,AGXT,YckA and GlnQ,showed expression trends consistent with transcriptome data.Metabolomic analysis identified 1153 metabolites predominantly enriched in histidine metabolism,lysine degradation,and arginine and proline metabolism.This study preliminarily elucidated the effect of high salt on the 5-HE synthesis pathway,and provided a basis for the subsequent construc-tion of 5-HE high-yielding strains.

To investigate the impact of high salt stress on the metabolic pathways and regulatory mecha-nisms involved in synthesizing hydroxyectoine(5-HE)in Virgibacillus salexigens,cultures were supple-mented with 1.5 and 2.5 mol/L NaCl as control and experimental groups,respectively.High-perform-ance liquid chromatography(HPLC)was used to detect the difference in the amount of 5-HE synthesis.Transcriptomic and metabolomic analyses identified differential genes and metabolites under varying salt concentrations.Key differential gene expressions related to 5-HE synthesis were validated using qRT-PCR.Results showed that 5-HE synthesis reached 121.9 mg/L at 2.5 mol/L NaCl.Transcriptomic anal-ysis identified 652 differentially expressed genes across 348 KEGG pathways,with 210 upregulated and 442 downregulated,primarily enriched in pathways such as purine metabolism,amino acid biosynthesis,sulfur metabolism,and biotin metabolism.Validation of 13 genes,including lysC,asd,ectA,ectB,ectC,ectD,thrB,thrC,ilvA,ilvE,AGXT,YckA and GlnQ,showed expression trends consistent with transcriptome data.Metabolomic analysis identified 1153 metabolites predominantly enriched in histidine metabolism,lysine degradation,and arginine and proline metabolism.This study preliminarily elucidated the effect of high salt on the 5-HE synthesis pathway,and provided a basis for the subsequent construc-tion of 5-HE high-yielding strains.