Huang J, Lacroix C, Daba H, Simard R E
Centre de recherche STELA, Université Laval, Ste-Foy, Québec, Canada.
J Appl Bacteriol. 1996 Jun;80(6):635-44. doi: 10.1111/j.1365-2672.1996.tb03268.x.
Continuous production of pediocin 5 from Pediococcus acidilactici UL5 was investigated in MRS medium at different pH and dilution rates during continuous free cell (FC) and immobilized cell (IC) fermentations. Pediocin 5 activity from FC operated at a dilution rate of 0.31 h-1 largely increased from 128 to 2048 AU mL-1 as pH decreased from 7.0 to 5.0. Pediocin 5 activity in IC at a dilution rate of 0.93 h-1 was much less affected by pH, varying from 256 AU mL-1 at pH 7.0 to 512 AU mL-1 at pH 5.0. At the optimum pH 5.0, the dilution rate greatly influenced pediocin 5 activity both in FC and IC. Pediocin 5 production during continuous FC culture decreased with time for all dilution rates tested except 0.31 h-1 and average activity over 144 h cultures reached a maximal value of 4915 AU mL-1 at a dilution rate of 0.26 h-1. For IC, pediocin 5 production was stable with time and increased with the dilution rate from 256 to 1024 AU mL-1 in the range of 0.47-2.28 h-1. Three Listeria strains were tested for their ability to screen low bacteriocin-producing variants (Bac+v) of Bac+ cells in FC and IC cultures by using a modified deferred antagonism method. Ten to 28% of Bac+v cells appeared after 144 h of FC cultures at dilution rates in the range 0.09-0.42 h-1 and pH control set points of 5.0-7.0 while almost no Bac+v cell was detected during 192 h IC culture in the same pH range and for dilution rates varying from 0.47 to 2.28 h-1. The Bac+v cells isolated produced eight- to 64-fold less pediocin 5 than the Bac+ cells. Although electrophoresis analysis showed no apparent difference in the plasmid profiles of Bac+v and Bac+ cells, the Bac- mutant obtained by acriflavine treatment had lost the pMJ5 plasmid encoding for bacteriocin production. The decreased quantity of plasmid DNA in Bac+v cells suggests that the decreased pediocin 5 activity of Bac+v cells resulted from a decrease in plasmid copy number.
在连续游离细胞（FC）和固定化细胞（IC）发酵过程中，研究了嗜酸乳杆菌UL5在不同pH值和稀释率的MRS培养基中连续生产片球菌素5的情况。在稀释率为0.31 h⁻¹的FC发酵中，随着pH值从7.0降至5.0，片球菌素5的活性从128 AU mL⁻¹大幅增加至2048 AU mL⁻¹。在稀释率为0.93 h⁻¹的IC发酵中，片球菌素5的活性受pH值的影响较小，在pH 7.0时为256 AU mL⁻¹，在pH 5.0时为512 AU mL⁻¹。在最佳pH 5.0时，稀释率对FC和IC发酵中的片球菌素5活性均有很大影响。在连续FC培养过程中，除了0.31 h⁻¹外，所有测试稀释率下片球菌素5的产量均随时间下降，在稀释率为0.26 h⁻¹的144小时培养中，平均活性达到最大值4915 AU mL⁻¹。对于IC发酵，片球菌素5的产量随时间稳定，在0.47 - 2.28 h⁻¹范围内，随着稀释率从256 AU mL⁻¹增加到1024 AU mL⁻¹。使用改良的延迟拮抗法，测试了三种李斯特菌菌株在FC和IC培养中筛选产细菌素能力低的细菌素产生变体（Bac + v）的能力。在稀释率为0.09 - 0.42 h⁻¹且pH控制点为5.0 - 7.0的FC培养144小时后，出现了10% - 28%的Bac + v细胞，而在相同pH范围内且稀释率为0.47 - 2.28 h⁻¹的192小时IC培养过程中，几乎未检测到Bac + v细胞。分离得到的Bac + v细胞产生的片球菌素5比Bac +细胞少8至64倍。虽然电泳分析显示Bac + v和Bac +细胞的质粒图谱没有明显差异，但通过吖啶黄素处理获得的Bac⁻突变体失去了编码细菌素产生的pMJ5质粒。Bac + v细胞中质粒DNA数量的减少表明，Bac + v细胞片球菌素5活性的降低是由于质粒拷贝数的减少。
