Optimizational production of phenyllactic acid by a Lactobacillus buchneri strain via uniform design with overlay sampling methodology

A Lactobacillus buchneri GBS3 strain isolated from the traditional Chinese pickles was used for the production of 3-phenyllactic acid(PLA), an important compound with antimicrobial activities against a wide species of grampositive and gram-negative bacteria and some fungi. The growth performance of this strain in the de Man, Rogosa and Sharpe(MRS) medium, the production of metabolites of valuable organic acids, and the biosynthesis of PLA using this strain as the whole-cell biocatalyst and phenylpyruvic acid(PPA) as the precursor, were investigated experimentally. The uniform design method with overlay sampling was developed for the optimization of the biotransformation conditions. The results showed that although it produced naturally lactic acid with the maximum concentration of 1.84 g·L^(-1) and PLA with the concentration of 0.015 g·L^(-1) after 66 to 72 h cultivation in MRS broth by fermentation, the present strain displayed an effective utilization ability by transforming PPA to PLA. By the uniform design method with overlay sampling for the design and optimization of transformation conditions, a maximum yield of 10.93 g·L^(-1) PLA with the mole conversion ratio of 83.07% from PPA to PLA was achieved under the optimized condition, i.e., 20 g·L^(-1) glucose, 270 g·L^(-1) cells, 13 g·L^(-1) PPA, pH 8.0 and the reaction time of 15 h, indicating that Lactobacillus buchneri GBS3 was an interesting strain for the biosynthesis of PLA via the microbial transformation. The prediction of PLA yield under different conditions was achieved successfully based on the limited information of only a small number of experiments by the uniform design with overlay sampling. Therefore, the present methodology is effective and helpful for the optimization of the biosynthesis processes of PLA.

Combined antibacterial and antibiofilm activity of phenyllactic acid and bacteriocin XJS01 against Shigella flexneri

This study investigated antibacterial and antibiofilm activity of the combined use of phenyllactic acid(PLA)and bacteriocin XJS01 against Shigella flexneri_14.The minimum inhibitory concentration(MIC)of PLA and XJS01 against S.flexneri_14 was 2.45 mg/mL and 18.75μg/mL,respectively.Growth and kill kinetics assays showed that the combined use of 1/2MIC PLA plus 1/2MIC XJS01 had a better activity against planktonic S.flexneri_14 compared to treatment with PLA and XJS01 used singly(1/2MIC and 2MIC).Cellular biochemical and morphological analysis revealed the remarkable ability of the combination in disrupting cell appearance and promoting deformation of planktonic S.flexneri_14 compared to single use.Moreover,S.flexneri_14 biofilm formation was inhibited and degraded by the combination,which showed a more remarkable antibiofilm activity than PLA and XJS01 when used singly.This study demonstrates the synergistic antibacterial activity of PLA and XJS01 against S.flexneri_14 in either planktonic or biofilm states in foods.