Ammonia Reduction by the GdhA and GlnA Genes from Bacteria in Laying Hens

Ammonia emissions are a high-focus pollution issue in the livestock industry. Ammonia-degrading bacteria can assimilate ammonia nitrogen as a nitrogen source to promote their growth and reproduction, providing an environmentally friendly, low-cost and safe biological way to reduce ammonia emissions from livestock. However, it remains unclear how ammonia-degrading bacteria reduce ammonia emissions from animals and what are the key ammonia assimilation genes. In the present study, two strains with ammonia nitrogen-degrading abilities (Enterococcus faecium strain C2 and Bacillus coagulans strain B1) were screened from laying chicken caecal and faecal samples and reduced ammonia emission rates by 53.60% and 31.38%, respectively. The expression levels of the ammonia assimilation genes gdhA, glnA, and GMPS increased significantly. On this basis, we successfully constructed three clone strains (PET-GDH, PET-GS, and PET-GMPS) that expressed the gdhA, glnA and GMPS genes in E. coli, respectively, to verify their ammonia-reducing activities. The results of an in vitro fermentation study showed that the ammonia production of the PET-GDH and PET-GS groups was significantly lower than that of the empty vector group (p < 0.05), with ammonia emission reduction rates of 55.5% and 54.8%, respectively. However, there was no difference between the PET-GMPS and empty vector groups. These results indicate that gdhA and glnA may be key genes involved in the bacterial-mediated regulation of ammonia emissions by laying hens, and ammonia emissions may be reduced by regulating their expression. The results of the present study provide a theoretical basis for the construction of engineered bacteria to reduce ammonia production in animals.