Isolation of Efficient Trimethylamine-Removing Strains and Optimization of Growth Conditions

Trimethylamine (TMA) is a typical nitrogen-containing amine organic pollutant, and one of the main malodorous gases causing odor pollution in animal husbandry. This gas is a harmful gas with a strong fishy odor. It not only causes point-source pollution in farming areas, but also its long-term exposure poses potential health risks to humans, attracting people's attention in recent years.

This study aimed to screen high-efficiency TMA-removing strains with strong degradation ability by collecting large amounts of animal manure, for providing excellent strains for the prevention and control of TMA pollution in livestock farming.

In this study, efficient TMA-removing strains were screened from the manures of pigs and cows by the methods of enrichment culture, isolation, purification, and deodorization ability measurement. Then the strains were identified using morphological observation and 16S rRNA gene analysis to determine their taxonomic characteristics. On this basis, the effects of different pH values (5.0, 6.0, 7.0, 8.0, and 9.0), carbon sources (glucose, sucrose, fructose, maltose, and xylose), salinities (0, 0.5%, 1.0%, 1.5%, and 2.0%), and inoculum concentrations (1%, 5%, 10%, 15%, and 20%) on bacterial biomass were further investigated to define the optimal growth conditions for the strains. Moreover, the actual deodorization effect of the efficient strains was verified by investigating the release concentration and removal rate of TMA during the initial stage of feces fermentation.

(1) A total of 10 TMA-removing strains, named T1 to T10, were isolated from livestock manure, among which strain T2 (Bacillus subtilis) and strain T3 (Acinetobacter sp.) exhibited the highest removal abilities of TMA. The TMA-removing rates after 48 h of incubation reached 26.91% for T2 and 29.59% for T3, which were higher than those of the other eight strains (P < 0.05). (2) Different pH values, carbon sources, salinities, and inoculum concentrations exerted varying effects on the growth of strains T2 and T3. Optimal growth conditions for T2 were as follows: pH=6.0, glucose as carbon source, 0.5% NaCl, and inoculum concentration of 1%; for T3, pH=8.0, sucrose as carbon source, 0.5% NaCl, and inoculum concentration of 1%. Under these optimal conditions above, the strains exhibited the fastest growth rate and achieved the maximum biomass. (3) The verification test of deodorization effect showed that when the feces were supplemented with T2 or T3, the average release amounts of TMA were lower than those in the control group (P < 0.01), and the highest removal rates reached 42.65% for T1 and 39.63% for T2.

Bacillus subtilis (T2) and Acinetobacter sp. (T3) isolated in this study had a high-efficiency ability to remove TMA, and would possess potential utilization value in the field of livestock manure treatment and control of pollution in animal husbandry.