固氮红细菌(Rhodobacter azotoformans) YLK20去除无机氮的影响因素

Factors affecting nitrogen removal from aquaculture wastewater by Rhodobacter azotoformans YLK20

摘要:

【背景】不产氧光合细菌(Anoxygenic phototrophic bacteria，APB)作为一类重要的微生物资源，在水产养殖水体氮污染的修复方面已有广泛研究与应用。养殖水体环境复杂，含多种有机物，尤其是有机氮显著影响菌体除氮功效。【目的】在高浓度无机三态氮(氨氮、硝氮和亚硝氮)共存体系中，阐明小分子有机碳、有机氮和盐度对固氮红细菌(Rhodobacter azotoformans) YLK20去除无机三态氮的影响规律及机制，挖掘针对性强和适应性广的高效除氮菌株。【方法】采用RAST和KEGG方法分析YLK20基因组碳氮代谢途径及耐盐机制；采用次溴酸钠氧化法、紫外和N-(1-萘基)-乙二胺分光光度法分别测定氨氮、硝氮和亚硝氮含量。【结果】基因组显示，YLK20拥有EMP、HMP、TCA、固氮、氨化、氨同化和反硝化碳氮代谢途径，含有sohB、nhaC、betB和gbsA等多种耐盐基因。丙酮酸钠、乙酸钠、柠檬酸钠、乙醇和甘露醇是YLK20生长和去除无机三态氮的良好有机碳，葡萄糖和果糖的存在降低了无机三态氮去除能力，蔗糖体系中硝氮和亚硝氮能被良好去除，但氨氮去除能力较低。在高浓度蛋白胨(3.21 g/L)和尿素(1.43 g/L)体系中，YLK20仍能高效去除无机三态氮。YLK20能在3%盐度内生长良好，低盐度时该菌株能良好去除无机三态氮，高盐度时亚硝氮去除能力受到严重抑制。YLK20对海水和淡水实际养殖水体中的无机三态氮有良好去除效果。【结论】 YLK20主要通过氨同化和反硝化途径去除无机三态氮，尤其在高浓度有机氮环境中也能高效去除；该菌株适应盐度范围广，兼可适用于淡水和海水养殖水体；该菌株生长和无机三态氮去除影响因素、规律及除氮机制的阐明，可为APB微生物制剂的合理应用提供指导。

Abstract:

[Background] Anoxygenic phototrophic bacteria (APB) have been widely investigated and applied in the bioremediation of nitrogen-polluted aquaculture. Various organic compounds are predominated in the contaminated aquaculture water, among them, organic nitrides significantly hamper the nitrogen removal efficiency. [Objective] In order to investigate the effects of organic compounds and salinity on inorganic nitrogen removal (ammonia, nitrate and nitrite) and elucidate the mechanism of inorganic nitrogen removal by Rhodobacter azotoformans YLK20, moreover, further to develop well-adapted microbial agents with high nitrogen removal efficiency. [Methods] RAST and KEGG analyses were used to elucidate carbon and nitrogen metabolic pathways and salt-tolerant mechanism(s) of YLK20. The removals of ammonia, nitrate and nitrite were measured by sodium hypobromite oxidation, UV spectrophotometry and N-(1-naphtyl)-ethylenediamine dihydrochloride spectrophoto-metric method, respectively. [Results] Genomic analysis revealed that YLK20 possesses EMP, HMP, TCA, nitrogen fixation, ammonium assimilation and ammonification and denitrification pathways. It contains several salt-tolerant genes such as sohB, nhaC, betB and gbsA. Pyruvate, acetate, citrate, ethanol and mannitol stimulated the cell growth and the nitrogen removal of YLK20, while glucose and fructose decreased the nitrogen removal level. Nitrate and nitrite were removed efficiently in the presence of sucrose while it is difficult to remove ammonia. In the presence of high concentration of peptone (3.21 g/L) and urea (1.43 g/L), inorganic nitrogen concentrations were significantly decreased. YLK20 was able to tolerate to at least 3% of NaCl, efficiently remove the inorganic nitrogen under low salinity conditions while nitrite removal was significantly inhibited in the presence of the high salinity. The inorganic nitrogen both from freshwater and marine rearing water could be efficiently removed by YLK20. [Conclusion] YLK20 could efficiently remove the inorganic nitrogen by ammonium assimilation and denitrification pathways, especially in the presence of high concentration of organics nitrogen. YLK20 was tolerant of high salinity, which is suitable for both freshwater aquaculture and marine aquaculture. YLK20 as a specific microecological modulator, was capable of removing efficiently nitrogen, showing the great potentials in the application in aquaculture remediation.