Isolation of High-Efficient Ammonia-Removing Strains and Its Cultivated Condition Optimization

Odor pollution from animal industry has become a pain point and a difficulty in recent years. Ammonia (NH₃) is an important harmful gas with great contribution rate to odor pollution, and its cutting emission becomes an urgent task. The objective of this study was to isolate the efficient NH₃-removing strains and to optimize its cultivated conditions, which would provide excellent strains for developing deodorizers.

Manure deposited in the sewage outlet of the farm was collected as the source of strain isolation. The NH₃-removing strains were enriched, separated, and purified using NH₃ enrichment culture medium. Then, the degradation ability of purified bacteria above was determined using NH₃-degradating culture medium, and the efficient NH₃-removing strains were screened. The isolated strains were identified by morphology (colony morphology and Gram staining) and 16S rRNA sequencing method. Further, the effects of various cultivated conditions on biomass of the strains, including pH (5.0, 6.0, 7.0, 8.0, and 9.0), carbon sources (xylose, sucrose, fructose, maltose, and glucose), salt contents (0%, 0.5%, 1.0%, 1.5%, and 2.0%), and inoculum amounts (1.0%, 5.0%, 10%, 15%, and 20%), were performed, and the optimal conditions were determined.

(1) A total of 12 suspected NH₃-degrading strains were isolated by enrichment culture (named as C1-C12), among of which, the strain named C5 had efficient NH₃-removing ability. The logarithmic growth period of the strain C5 was 2 to 20 h. During the period, the degradation rate of C5 increased with the growing bacteria biomass, reaching 60.70% at 24 h and 75.49% at 48 h of culture, respectively, which was greater than that of the other 11 strains in the same time (P<0.05). From morphology and 16S rRNA identification, the C5 was characterized by stubby- and rod-shaded, pointless round at both ends, and no capsule, as well as Gram-negative bacteria. Combined with gene sequencing results and phylogenetic tree, the C5 was determined to be Klebsiella pneumoniae. (2) Various pH values, carbon sources, salt content, and inoculation amount showed different effects on the concentration of C5 after 48 h of culture. The C5 concentration at pH 7.0 was greater than that at pH 5.0, pH 6.0 and pH 9.0 (P<0.05). Compared with other carbon sources, the C5 concentration for glucose as carbon source was the greatest during the culture period of 8 to 48 h. Under different salt content and inoculation amount, there were differences (P<0.01) in bacterial concentration between groups, exhibiting the greatest concentration of bacterial solution at 1.5% salt and a peak value at 40 h of culture. Besides, the fast growth of bacteria was observed for 1.0% of inoculation amount and bacterial concentration increased, compared with other inoculation amounts. Therefore, the optimal growing conditions of the C5 were as follows: pH=7.0, carbon source of glucose, 1.5% salt content, and 1.0% of inoculum amount, where the growth rate and biomass of the C5 were optimal.

Klebsiella pneumoniae (strain C5) isolated from manure possessed the ability to remove NH₃ efficiently, which would have potential utilization value in livestock manure treatment.