Using Lactococcus garvieae S5-4 preserved from the pre-screening of the laboratory as the starting strain,the original strain S5-4 was mutat-ed by multiple rounds of atmospheric and room temperature plasma-ultraviolet(ARTP-UV)compound mutagenesis.Esterase activity was used as evaluation index,and a high-yield esterase mutant strain ARUV3-26 was obtained,with an esterase activity of(25.88±0.02)U/ml,which was 64.42％higher than the original strain S5-4.After 15 generations of passage testing,the esterase activities of the mutant strain ARUV3-26 remained stable at(23.51±0.02)to(23.56±0.02)U/ml,which was 49.36％to 49.68％higher than that of the original strain S5-4.Physiological tolerance tests showed that the temperature tolerance,pH tolerance,glucose tolerance,ethanol tolerance,butyric acid and caproic acid tolerance of the mutant strain ARUV3-26 were improved compared with the original strain S5-4.Through single-factor tests optimization,the optimal medium compositions were obtained as follows:glucose 20 g/L,peptone 15 g/L,and NaCl 5 g/L.Through single-factor and response surface experiments,the optimal fermentation conditions were determined as follows:fermentation time 3.0 d,fermentation temperature 30 ℃,and initial pH value 7.0.Under these optimal conditions,the esterase activity of the mutant strain ARUV3-26 was(30.67±0.17)U/ml,which was 30.45％higher than the esterase production capacity of the original strain S5-4.
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