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Addressing the critical challenge for rhamnolipid production: discontinued synthesis in extended stationary phase
Process Biochemistry ( IF 4.4 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.procbio.2019.11.036
Maysam Sodagari , Lu-Kwang Ju

Abstract Rhamnolipids are commonly produced using N-limited Pseudomonas aeruginosa fermentations, with active production in the stationary phase. The production, however, stops after certain period. This causes lower productivity and yield because of downtime between batches and the substrate consumed for cell growth. This discontinued production is the significant problem addressed in this study. Rhamnolipid synthesis involves complex regulatory mechanisms, including quorum-sensing systems and alternative sigma factors. Current knowledge on these mechanisms, however, cannot adequately explain the discontinued rhamnolipid production at extended stationary phase. Four hypotheses to causes of this discontinued production were examined here with carefully planned fermentation designs using different initial N-source concentrations and different ways of adding oil and nutrients. Results rejected three of the hypothetical causes: accumulation of rhamnolipids or other inhibitory metabolites, presence of high amounts of oil phase, and exhaustion of non-N nutrients, and supported the hypothesis that the stopped production was caused solely by the extended N-starvation experienced by the cells. The discontinued production was found to be fully reactivated by partial broth replacements with fresh media containing N-source. The finding is important to production economics and promotes new designs to maximize rhamnolipid productivity and yield using extended stationary-phase production instead of short repeated batches.

中文翻译:

解决鼠李糖脂生产的关键挑战:在延长的固定相中停止合成

摘要 鼠李糖脂通常使用限氮铜绿假单胞菌发酵生产,在稳定期生产活跃。但是,生产会在一段时间后停止。由于批次之间的停机时间和细胞生长消耗的底物,这会导致生产率和产量降低。这种停产是本研究中解决的重要问题。鼠李糖脂合成涉及复杂的调节机制,包括群体感应系统和替代 sigma 因子。然而,目前关于这些机制的知识并不能充分解释延长固定相时鼠李糖脂生产的中断。这里通过仔细规划的发酵设计,使用不同的初始氮源浓度和不同的添加油和营养物质的方式,检查了导致这种停产原因的四个假设。结果拒绝了三个假设原因:鼠李糖脂或其他抑制性代谢物的积累、大量油相的存在以及非 N 营养物的耗尽,并支持停止生产仅由经历的长期 N-饥饿引起的假设由细胞。通过用含有 N 源的新鲜培养基替代部分肉汤,发现已中断的生产完全重新激活。
更新日期:2020-04-01
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