Bovicin HC5 is a peptide that has inhibitory activity against various pathogenic microorganisms and food spoilage bacteria. Aiming to improve the productivity of this bacteriocin, we evaluated several potential factors that could stimulate the synthesis of bovicin HC5 and selected variants of Streptococcus equinus (Streptococcus bovis) HC5 with enhanced bacteriocin production by adaptive laboratory evolution (ALE). The highest production of the bacteriocin (1.5-fold) was observed when Strep. equinus HC5 was cultivated with lactic acid (100 mmol/L). For the ALE experiment, Strep. equinus HC5 cells were subjected to acid-shock (pH 3.0 for 2 h) and maintained in continuous culture for approximately 140 generations (40 days) in media with lactic acid (100 mmol/L) and pH-controlled at 5.5 ± 0.2. An adapted variant was selected showing a distinct phenotype (sedimentation, pigmentation) compared with the parental strain. Bacteriocin production increased 2-fold in this adapted Strep. equinus HC5 variant, which appears to be associated with changes in the cell envelope of the adapted variant and enhanced bacteriocin release into the culture media. In addition, the adapted variant showed higher levels of expression of all bovicin HC5 biosynthetic genes compared with the parental strain during the early and late stages of growth. Results presented here indicate that ALE is a promising strategy for selecting strains of lactic acid bacteria with increased production of bacteriocins.

Bovicin HC5是一种对多种病原微生物和食品腐败菌具有抑制活性的肽。为了提高这种细菌素的生产力，我们评估了几个潜在因素，这些因素可以刺激 bovicin HC5 的合成，以及通过适应性实验室进化 (ALE) 增强细菌素产量的马链球菌( Streptococcus bovis ) HC5 的选定变体。当Strep时观察到细菌素的最高产量（1.5 倍）。用乳酸 (100 mmol/L) 培养马马HC5。对于 ALE 实验，Strep。马匹HC5 细胞经受酸休克（pH 3.0 2 小时），并在含有乳酸（100 mmol/L）和 pH 控制在 5.5 ± 0.2 的培养基中连续培养约 140 代（40 天）。与亲本菌株相比，选择了一种显示出不同表型（沉淀、色素沉着）的适应变体。在这种适应的链球菌中，细菌素产量增加了 2 倍。马匹HC5 变体，这似乎与适应变体的细胞包膜的变化和增加的细菌素释放到培养基中有关。此外，在生长的早期和晚期阶段，与亲本菌株相比，适应的变体显示出所有 bovicin HC5 生物合成基因的表达水平更高。这里呈现的结果表明，ALE 是一种很有前景的策略，用于选择细菌素产量增加的乳酸菌菌株。