Björkmalm Johanna, Byrne Eoin, van Niel Ed W J, Willquist Karin
1Department of Energy and Circular Economy, RISE Research Institutes of Sweden, PO Box 857, 501 15 Borås, Sweden.
2Division of Applied Microbiology, Lund University, PO Box 124, 221 00 Lund, Sweden.
Biotechnol Biofuels. 2018 Jun 22;11:175. doi: 10.1186/s13068-018-1171-3. eCollection 2018.
is an attractive hydrogen producer suitable for growth on various lignocellulosic substrates. The aim of this study was to quantify uptake of pentose and hexose monosaccharides in an industrial substrate and to present a kinetic growth model of that includes sugar uptake on defined and industrial media. The model is based on Monod and Hill kinetics extended with gas-to-liquid mass transfer and a cybernetic approach to describe diauxic-like growth.
Mathematical expressions were developed to describe hydrogen production by consuming glucose, xylose, and arabinose. The model parameters were calibrated against batch fermentation data. The experimental data included four different cases: glucose, xylose, sugar mixture, and wheat straw hydrolysate (WSH) fermentations. The fermentations were performed without yeast extract. The substrate uptake rate of on single sugar-defined media was higher on glucose compared to xylose. In contrast, in the defined sugar mixture and WSH, the pentoses were consumed faster than glucose. Subsequently, the cultures entered a lag phase when all pentoses were consumed after which glucose uptake rate increased. This phenomenon suggested a diauxic-like behavior as was deduced from the successive appearance of two peaks in the hydrogen and carbon dioxide productivity. The observation could be described with a modified diauxic model including a second enzyme system with a higher affinity for glucose being expressed when pentose saccharides are consumed. This behavior was more pronounced when WSH was used as substrate.
The previously observed co-consumption of glucose and pentoses with a preference for the latter was herein confirmed. However, once all pentoses were consumed, most probably expressed another uptake system to account for the observed increased glucose uptake rate. This phenomenon could be quantitatively captured in a kinetic model of the entire diauxic-like growth process. Moreover, the observation indicates a regulation system that has fundamental research relevance, since pentose and glucose uptake in has only been described with ABC transporters, whereas previously reported diauxic growth phenomena have been correlated mainly to PTS systems for sugar uptake.
[具体微生物名称]是一种有吸引力的产氢菌，适合在各种木质纤维素底物上生长。本研究的目的是量化工业底物中戊糖和己糖单糖的摄取量，并提出[具体微生物名称]的动力学生长模型，该模型包括在限定培养基和工业培养基上的糖摄取情况。该模型基于莫诺德动力学和希尔动力学，并扩展了气液传质以及用控制论方法来描述类双相生长。
开发了数学表达式来描述[具体微生物名称]消耗葡萄糖、木糖和阿拉伯糖产生氢气的过程。模型参数根据分批发酵数据进行了校准。实验数据包括四种不同情况：葡萄糖、木糖、糖混合物和小麦秸秆水解物（WSH）发酵。发酵过程中未添加酵母提取物。在单一糖限定培养基上，[具体微生物名称]对葡萄糖的底物摄取速率高于木糖。相比之下，在限定糖混合物和WSH中，戊糖的消耗速度比葡萄糖快。随后，当所有戊糖被消耗完后，培养物进入滞后期，之后葡萄糖摄取速率增加。这种现象表明存在类双相行为，这是从氢气和二氧化碳生产率中相继出现的两个峰值推断出来的。这种观察结果可以用一个改进的双相模型来描述，该模型包括一个在戊糖消耗时表达的对葡萄糖具有更高亲和力的第二种酶系统。当使用WSH作为底物时，这种行为更为明显。
本文证实了之前观察到的葡萄糖和戊糖共同消耗且更偏好后者的现象。然而，一旦所有戊糖被消耗完，[具体微生物名称]很可能表达了另一种摄取系统来解释观察到的葡萄糖摄取速率增加的现象。这种现象可以在整个类双相生长过程的动力学模型中进行定量描述。此外，该观察结果表明了一个具有基础研究意义的调节系统，因为[具体微生物名称]中戊糖和葡萄糖的摄取仅用ABC转运蛋白进行了描述，而之前报道的双相生长现象主要与糖摄取的磷酸转移酶系统相关。
