Screening and metabolomic analysis of a fungal strain efficiently assimilating ammonia nitrogen

Abstract:

[Objective] To screen out a fungal strain that can efficiently assimilate ammonia nitrogen, reveal the metabolome differences of the strain in different media and the changes in the amino acid content of the feed fermented with the strain, and clarify the mechanism of its ammonia assimilation. [Methods] Seven strains of Trichoderma, 7 strains of Aspergillus niger, and 9 strains of Aspergillus oryzae were cultured in the media with (NH₄)₂SO₄ as the only nitrogen source. The strains with high ammonia nitrogen use efficiency and glutamine synthetase (GS) activity were selected for comparison of the metabolic differences in potato dextrose agar (PDA) plates and inorganic nitrogen plates by non-targeted metabonomics. Furthermore, the crude protein and organic nitrogen content in the feed fermented with different strains was determined, and the changes in amino acid content in the fermented feed extract were measured by amino acid-targeted metabolomics. [Results] The utilization rate of ammonia nitrogen and the glutamine synthetase activity of A. oryzae MQ28 were 54.46% and 0.61 μmol/(h·g), respectively, which were higher than those of other strains (P<0.05). The comparative metabonomics analysis suggested that MQ28 was associated with the metabolism of multiple amino acids during ammonia assimilation. MQ28 fermentation increased the crude protein and organic nitrogen in the feed by 22.25% and 35.83% (P<0.05), respectively. Furthermore, MQ28 fermentation increased the total amino acid content in feed extract from 31.86 mmol/100 g to 57.69 mmol/100 g (P<0.05). Specifically, it increased the content of 14 amino acids such as threonine, lysine, and arginine, glutamic acid (by 3.46 folds), and glutamine (by 99 folds) (P<0.05). [Conclusion] To sum up, A. oryzae MQ28 has high ammonia nitrogen utilization capacity. It may regulate the ammonia assimilation process through the synthesis of glutamine to regulate amino acid metabolism and can be used as an elite strain for the production of single-cell protein.