Li Z J, Shukla V, Fordyce A P, Pedersen A G, Wenger K S, Marten M R
Department of Chemical and Biochemical Engineering, University of Maryland, Baltimore County (UMBC),1000 Hilltop Circle, Baltimore, Maryland 21250, USA.
Biotechnol Bioeng. 2000 Nov 5;70(3):300-12. doi: 10.1002/1097-0290(20001105)70:3<300::aid-bit7>3.0.co;2-3.
It is well known that high-viscosity fermentation broth can lead to mixing and oxygen mass transfer limitations. The seemingly obvious solution for this problem is to increase agitation intensity. In some processes, this has been shown to damage mycelia, affect morphology, and decrease product expression. However, in other processes increased agitation shows no effect on productivity. While a number of studies discuss morphology and fragmentation at the laboratory and pilot scale, there are relatively few publications available for production-scale fungal fermentations. The goal of this study was to assess morphology and fragmentation behavior in large-scale, fed-batch, fungal fermentations used for the production of protein. To accomplish this, a recombinant strain of Aspergillus oryzae was grown in 80 m(3) fermentors at two different gassed, impeller power-levels (one 50% greater than the other). Impeller power is reported as energy dissipation/circulation function (EDCF) and was found to have average values of 29.3 +/- 1.0 and 22.0 +/- 0.3 kW m(-3) s(-1) at high and low power levels, respectively. In all batches, biomass concentration profiles were similar and specific growth rate was < 0.03 h(-1). Morphological data show hyphal fragmentation occurred by both shaving-off of external clump hyphae and breakage of free hyphae. The fragmentation rate constant (k(frag)), determined using a first-order model, was 5.90 and 5.80 h(-1) for high and low power batches, respectively. At the end of each batch, clumps accounted for only 25% of fungal biomass, most of which existed as small, sparsely branched, free hyphal elements. In all batches, fragmentation was found to dominate fungal growth and branching. We speculate that this behavior was due to slow growth of the culture during this fed-batch process.
众所周知，高粘度发酵液会导致混合和氧气传质受限。对于这个问题，看似显而易见的解决办法是提高搅拌强度。在某些工艺中，这已被证明会损害菌丝体，影响形态，并降低产物表达。然而，在其他工艺中，增加搅拌对生产率没有影响。虽然有许多研究在实验室和中试规模讨论了形态和破碎情况，但关于生产规模真菌发酵的出版物相对较少。本研究的目的是评估用于蛋白质生产的大规模补料分批真菌发酵中的形态和破碎行为。为了实现这一目标，将米曲霉的重组菌株在80立方米的发酵罐中，于两种不同的通气叶轮功率水平下培养（一种比另一种高50%）。叶轮功率以能量耗散/循环函数（EDCF）表示，发现在高功率和低功率水平下，其平均值分别为29.3±1.0和22.0±0.3千瓦·米-3·秒-1。在所有批次中，生物量浓度曲线相似，比生长速率<0.03小时-1。形态学数据表明，菌丝破碎是通过外部菌团菌丝的削落和游离菌丝的断裂发生的。使用一级模型确定的破碎速率常数（k(frag)），高功率批次和低功率批次分别为5.90和5.80小时-1。在每个批次结束时，菌团仅占真菌生物量的25%，其中大部分以小的、分支稀疏的游离菌丝体形式存在。在所有批次中，发现破碎主导了真菌的生长和分支。我们推测这种行为是由于在这个补料分批过程中培养物生长缓慢所致。
