Screening of lactic acid bacteria after N+ implantation and its effects on alfalfa silage quality

Low soluble sugar content of alfalfa (Medicago sativa), which effects the acid production of lactic acid bacteria (LAB) additives, is one of the important factors that influences its silage quality. In this study, cellulolytic activities of lactic acid bacteria were enhanced by N+ implantation to improve their acid production capabilities in alfalfa ensiling. Lactobacillus plantarumstrain ZZU A345 with high antimicrobial activity and good acid production ability was treated with a N+ ion beam and the mutant strains zw2-21 and zw3-57 were screened out with good degradation of sodium carboxymethyl cellulose. The activity levels for alfalfa meal acidification of the two strains was significantly higher (P<0.05) than that of ZZU A345, and the activity of cellulase endonuclease was also higher than that of ZZU A345, but no significant difference was found. Results for 65 d alfalfa ensiling showed that the pH of the treatment with zw2-21 decreased to 4.83, which was significantly lower (P<0.05) than that of the blank control group with no LAB additive (pH 5.5). It was also lower than that of the treatment with ZZU A345 (pH 5.08), but there was no significant difference. Content of lactic acid in the treatment with zw2-21 reached 1.22%, which was one time more than the content in the treatment with ZZU A345. We concluded that N+ implantation has potential application for improving the performance of LAB in cellulose degradation and acid production in alfalfa ensiling.