Abstract

In this study, genome shuffling was conducted to improve the propionate production and acid-tolerance of the wild-type strain Megasphaera elsdenii H6. The initial mutant population of M. elsdenii H6 was treated with UV irradiation and nitrosoguanidine (NTG), resulting in an improved population producing more propionate than the original strain at pH 5.5. These mutants were used as the starting strains for 3 rounds of genome shuffling. After each round, the pH of the medium plates used for selection was decreased by 0.2. The improved strains were selected based on their acid tolerance and propionate production. Apparent acid tolerance of the mutants on the gradient plate increased progressively with each round of shuffling up to 3 rounds. After three rounds of genome shuffling, the mutant F32 of M. elsdenii H6 grew at pH 4.8 and the yield of propionate was increased to 151.02% compared with the original strain. The mutant F32 could be potential candidates for preventing rumen acidosis and production disease.

Key words: Genome shuffling, Megasphaera elsdenii, acid-tolerance, propionate.