Pongtharangkul Thunyarat, Demirci Ali
Department of Agricultural and Biological Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
Appl Microbiol Biotechnol. 2006 Nov;73(1):73-9. doi: 10.1007/s00253-006-0459-6. Epub 2006 May 30.
A biofilm reactor not only shortens the lag phase of nisin production, but also enhances nisin production when combined with an appropriate pH profile. Due to the substrate inhibition that takes place at high levels of carbon source, fed-batch fermentation was proposed as a better alternative for nisin production. In this study, the combined effects of fed-batch fermentation and various pH profiles on nisin production in a biofilm reactor were evaluated. The tested pH profiles include 1) a constant pH profile at 6.8 (profile 1), 2) a constant pH profile with an autoacidification after 4 h (profile 2), and 3) a step-wise pH profile with pH adjustment every 2 h (profile 3). When profile 1 was applied, fed-batch fermentation enhanced nisin production for both suspended-cell (4,188 IU ml(-1)) and biofilm (4,314 IU ml(-1)) reactors, yielded 1.8- and 2.3-fold higher nisin titer than their respective batch fermentation. On the other hand, pH profiles that include periods of autoacidification (profiles 2 and 3) resulted in a significantly lower nisin production in fed-batch fermentation (2,494 and 1,861 IU ml(-1) for biofilm reactor using profile 2 and 3, respectively) due to toxicity of excess lactic acid produced during the fermentation. Overall, this study suggested that fed-batch fermentation can be successfully used to enhance nisin production for both suspended-cell and biofilm reactors.
生物膜反应器不仅缩短了乳酸链球菌素生产的延迟期，而且与合适的pH曲线相结合时还能提高乳酸链球菌素的产量。由于在高浓度碳源下会发生底物抑制，因此提出补料分批发酵是生产乳酸链球菌素的更好选择。在本研究中，评估了补料分批发酵和各种pH曲线对生物膜反应器中乳酸链球菌素生产的综合影响。测试的pH曲线包括：1）pH值恒定在6.8的曲线（曲线1），2）4小时后自动酸化的恒定pH曲线（曲线2），以及3）每2小时进行pH调节的逐步pH曲线（曲线3）。应用曲线1时，补料分批发酵提高了悬浮细胞反应器（4,188 IU ml(-1)）和生物膜反应器（4,314 IU ml(-1)）的乳酸链球菌素产量，其乳酸链球菌素效价比各自的分批发酵分别高出1.8倍和2.3倍。另一方面，包括自动酸化阶段的pH曲线（曲线2和曲线3）导致补料分批发酵中乳酸链球菌素产量显著降低（使用曲线2和3的生物膜反应器分别为2,494和1,861 IU ml(-1)），这是由于发酵过程中产生的过量乳酸具有毒性。总体而言，本研究表明补料分批发酵可成功用于提高悬浮细胞和生物膜反应器中乳酸链球菌素的产量。
