Development and validation of polar RP-HPLC method for screening for ectoine high-yield strains in marine bacteria with green chemistry

The synthesis of ectoine enhance the assimilation of ammonia nitrogen in hypersaline wastewater by the salt-tolerant assimilation bacteria sludge

In contrast to nitrification-denitrification microorganisms that convert ammonia nitrogen in hypersaline wastewater into nitrogen for discharge, this research utilizes sludge enriched with salt-tolerant assimilation bacteria (STAB) to assimilate organic matter and ammonia nitrogen in hypersaline wastewater into ectoine - a biomass with high economic value and resistance to external osmotic pressure. The study investigates the relationship between the synthesis of ectoine and nitrogen removal efficiency of STAB sludge in three sequencing batch reactors (SBR) operated at different salinities (50, 75, and 100 g/L) and organic matter concentrations. The research reveals that, under low concentration carbon sources (TOC/N = 4, NH4+-N = 60 mg/L), the ammonia nitrogen removal efficiency of SBR reactors increased by 14.51 % and 17.25 % within 5 d and 2 d, respectively, when salinity increased from 50 g/L to 75 g/L and 100 g/L. Under high concentration carbon sources (TOC/N = 8, NH4+-N = 60 mg/L), the ammonia nitrogen removal efficiency of STAB sludge in the three reactors stabilized at 80.20 %, 76.71 %, and 72.87 %, and the total nitrogen removal efficiency was finally stabilized at 80.47 %, 73.15 %, and 65.53 %, respectively. The nitrogen removal performance by ammonium-assimilating of STAB sludge is more sustainable under low salinity, while it is more short-term explosive under high salinity. Moreover, the intracellular ectoine concentration of STAB sludge was found to be related to this behavior. Empirical formulas confirm that STAB sludge synthesizes ectoine from nutrients in wastewater through assimilation, and intracellular ectoine has a threshold defect (150 mg/gVss). The ectoine metabolism pathways of STAB sludge was constructed using the Kyoto Encyclopedia of Genes and Genomes (KEGG). The ammonia nitrogen in sewage is converted into glutamic acid under the action of assimilation genes. It then undergoes a tricarboxylic acid cycle to synthesize the crucial precursor of ectoine - aspartic acid. Subsequently, ectoine is produced through ectoine synthase. The findings suggest that when the synthesis of intracellular ectoine reaches saturation, it inhibits the continuous nitrogen removal performance of STAB sludge under high salinity. STAB sludge does not actively release ectoine through channels under stable external osmotic pressure.

Isolation of three polyoxins by reversed-phase liquid chromatography with pure aqueous mobile phase

Developing methods for the isolation of highly polar compounds from complex samples is of great significance. In this study, three polyoxins were successfully isolated from a complex sample (PN1-1^# ) by preparative high-performance liquid chromatography. Separation was carried out on five polar reversed-phase stationary phases, using pure aqueous as mobile phase, where the C18HC column can provide the best performance for PN1-1^# . Next, the effects of the mobile phase composition were studied. It was found that adding NaClO₄ can enhance the retention and resolution, and adding NaH₂ PO₄ was beneficial to maintain good peak shapes when the sample loading increased. Therefore, the optimized mobile phase consisting of 20 mmol NaH₂ PO₄ and 20 mmol NaClO₄ (adding H₃ PO₄ to adjust pH 2) was used to separate PN1-1^# . This method of using 100% aqueous phase can effectively improve both the retention and the solubility of polar samples. Eventually, through further purification, three compounds, namely, polyoxins B, D, and G, were obtained. This paper provided an effective and eco-friendly strategy for the preparative-scale separation of polar samples.