Laboratory for Biomaterials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St. Gallen, Switzerland.
Biotechnol Bioeng. 2012 Feb;109(2):451-61. doi: 10.1002/bit.23312. Epub 2011 Aug 31.
The success of bioprocess implementation relies on the ability to achieve high volumetric productivities and requires working with high-cell-density cultivations. Elevated atmospheric pressure might constitute a promising tool for enhancing the oxygen transfer rate (OTR), the major growth-limiting factor for such cultivations. However, elevated pressure and its effects on the cellular environment also represent a potential source of stress for bacteria and may have negative effects on product formation. In order to determine whether elevated pressure can be applied for enhancing productivity in the case of medium-chain-length polyhydroxyalkanoate (mcl-PHA) production by Pseudomonas putida KT2440, the impact of a pressure of 7 bar on the cell physiology was assessed. It was established that cell growth was not inhibited by this pressure if dissolved oxygen tension (DOT) and dissolved carbon dioxide tension (DCT) were kept below ∼30 and ∼90 mg L(-1), respectively. Remarkably, a little increase of mcl-PHA volumetric productivity was observed under elevated pressure. Furthermore, the effect of DCT, which can reach substantial levels during high-cell-density processes run under elevated pressure, was investigated on cell physiology. A negative effect on product formation could be dismissed since no significant reduction of mcl-PHA content occurred up to a DCT of ∼540 mg L(-1). However, specific growth rate exhibited a significant decrease, indicating that successful high-cell-density processes under elevated pressure would be restricted to chemostats with low dilution rates and fed-batches with a small growth rate imposed during the final part. This study revealed that elevated pressure is an adequate and efficient way to enhance OTR and mcl-PHA productivity. We estimate that the oxygen provided to the culture broth under elevated pressure would be sufficient to triple mcl-PHA productivity in our chemostat system from 3.4 (at 1 bar) to 11 g L(-1)h(-1) (at 3.2 bar).
生物工艺实施的成功依赖于实现高容积产率的能力，并且需要进行高细胞密度培养。提高大气压力可能是提高氧传递速率（OTR）的有前途的工具，OTR 是此类培养的主要生长限制因素。然而，高压及其对细胞环境的影响也代表了细菌潜在的应激源，并可能对产物形成产生负面影响。为了确定在 7 巴的压力下是否可以应用于提高生产能力，在 Pseudomonas putida KT2440 生产中链长聚羟基烷酸酯（mcl-PHA）的情况下，评估了压力对细胞生理学的影响。如果溶解氧张力（DOT）和溶解二氧化碳张力（DCT）分别保持在约 30 和 90mg/L 以下，则确定该压力不会抑制细胞生长。值得注意的是，在高压下观察到 mcl-PHA 容积产率略有增加。此外，还研究了在高细胞密度过程中可以达到相当水平的 DCT 对细胞生理学的影响。由于在 DCT 高达约 540mg/L 时没有发生 mcl-PHA 含量的显著降低，因此可以排除对产物形成的负面影响。然而，比生长速率显著降低，表明在高压下成功的高细胞密度过程将仅限于具有低稀释率的恒化器和在最后部分施加低生长速率的分批补料。这项研究表明，提高压力是提高 OTR 和 mcl-PHA 产率的合适且有效的方法。我们估计，在高压下提供给培养基的氧气足以将我们的恒化器系统中的 mcl-PHA 产率从 3.4（在 1 巴）提高到 11g/L/h（在 3.2 巴），提高三倍。
