Sampaio Fábio C, Torre Paolo, Passos Flávia M Lopes, Perego Patrizia, Passos Frederico J Vieira, Converti Attilio
Department of Microbiology, Federal University of Viçosa, Av. P. H. Rolfs s/n, 36571-000 Viçosa, Minas Gerais, Brazil.
Biotechnol Prog. 2004 Nov-Dec;20(6):1641-50. doi: 10.1021/bp049691j.
The new yeast Debaryomyces hansenii UFV-170 was tested in this work in batch experiments under variable oxygenation conditions. To get additional information on its fermentative metabolism, a stoichiometric network was proposed and checked through a bioenergetic study performed using the experimental data of product and substrate concentrations. The yeast metabolism resulted to be practically inactive under strict oxygen-limited conditions (qO2 = 12.0 mmol(O2) C-mol(DM)(-1) h(-1)), as expected by the impossibility of regenerating NADH2+. Significant fractions of the carbon source were addressed to both respiration and biomass growth under excess oxygen levels (qO2 > or = 55.0 mmol(O2) C-mol(DM)(-1) h(-1)), thus affecting xylitol yield (Y(P/S) = 0.41-0.52 g g(-1)). Semi-aerobic conditions (qO2 = 26.8 mmol(O2) C-mol(DM)(-1) h(-1)) were able to ensure the best xylitol production performance (Pmax = 76.6 g L(-1)), minimizing the fractions of the carbon source addressed either to respiration or biomass production and increasing Y(P/S) up to 0.73 g g(-1). An average P/O ratio of about 1.0 mol(ATP) mol(O)(-1) allowed estimation of the main kinetic-bioenergetic parameters of the biosystem. The overall ATP requirements of biomass were found to be particularly high and dependent on the oxygen availability in the medium as well as on the physiological state of the culture. Under semi-aerobic and aerobic conditions, they varied in the ranges 13.5-15.4 and 9.74-10.2 mol(ATP) C-mol(DM)(-1), respectively, whereas during the best semi-aerobic bioconversion they progressively increased from 5.68 to 24.7 mol(ATP) C-mol(DM)(-1). After a starting phase of adaptation to the medium, the cell achieved a phase of decelerated growth during which its excellent xylose-to-xylitol capacity kept almost constant after 112 h up to the end of the run.
在本研究中，新型酵母汉逊德巴利酵母UFV - 170在不同充氧条件下进行了分批实验。为了获取其发酵代谢的更多信息，构建了一个化学计量网络，并通过利用产物和底物浓度的实验数据进行生物能量学研究来进行验证。正如预期的那样，由于无法再生NADH2 +，在严格的氧限制条件下（qO2 = 12.0 mmol(O2) C - mol(DM)(-1) h(-1)），酵母代谢实际上处于无活性状态。在过量氧水平下（qO2 ≥ 55.0 mmol(O2) C - mol(DM)(-1) h(-1)），相当一部分碳源用于呼吸作用和生物量生长，从而影响木糖醇产量（Y(P/S) = 0.41 - 0.52 g g(-1)）。半好氧条件（qO2 = 26.8 mmol(O2) C - mol(DM)(-1) h(-1)）能够确保最佳的木糖醇生产性能（Pmax = 76.6 g L(-1)），使用于呼吸作用或生物量生产的碳源比例最小化，并将Y(P/S)提高到0.73 g g(-1)。约1.0 mol(ATP) mol(O)(-1)的平均P/O比有助于估算生物系统的主要动力学 - 生物能量学参数。发现生物量的总体ATP需求特别高，并且取决于培养基中的氧可用性以及培养物的生理状态。在半好氧和好氧条件下，它们分别在13.5 - 15.4和9.74 - 10.2 mol(ATP) C - mol(DM)(-1)范围内变化，而在最佳半好氧生物转化过程中，它们从5.68逐渐增加到24.7 mol(ATP) C - mol(DM)(-1)。在适应培养基的起始阶段之后，细胞进入生长减速阶段，在此期间，其出色的木糖转化为木糖醇的能力在112小时后直至运行结束几乎保持恒定。
