Islam Rumana, Cicek Nazim, Sparling Richard, Levin David
Deptartment of Biosystems Engineering, University of Manitoba, Winnipeg, R3T 5V6 MB, Canada.
Appl Microbiol Biotechnol. 2006 Sep;72(3):576-83. doi: 10.1007/s00253-006-0316-7. Epub 2006 May 10.
We have investigated hydrogen (H2) production by the cellulose-degrading anaerobic bacterium, Clostridium thermocellum. In the following experiments, batch-fermentations were carried out with cellobiose at three different substrate concentrations to observe the effects of carbon-limited or carbon-excess conditions on the carbon flow, H2-production, and synthesis of other fermentation end products, such as ethanol and organic acids. Rates of cell growth were unaffected by different substrate concentrations. H2, carbon dioxide (CO2), acetate, and ethanol were the main products of fermentation. Other significant end products detected were formate and lactate. In cultures where cell growth was severely limited due to low initial substrate concentrations, hydrogen yields of 1 mol H2/mol of glucose were obtained. In the cultures where growth ceased due to carbon depletion, lactate and formate represented a small fraction of the total end products produced, which consisted mainly of H2, CO2, acetate, and ethanol throughout growth. In cultures with high initial substrate concentrations, cellobiose consumption was incomplete and cell growth was limited by factors other than carbon availability. H2-production continued even in stationary phase and H2/CO2 ratios were consistently greater than 1 with a maximum of 1.2 at the stationary phase. A maximum specific H2 production rate of 14.6 mmol g dry cell(-1) h(-1) was observed. As cells entered stationary phase, extracellular pyruvate production was observed in high substrate concentration cultures and lactate became a major end product.
我们研究了纤维素降解厌氧细菌热纤梭菌（Clostridium thermocellum）的产氢情况。在接下来的实验中，以三种不同底物浓度的纤维二糖进行分批发酵，以观察碳限制或碳过量条件对碳流、产氢以及其他发酵终产物（如乙醇和有机酸）合成的影响。细胞生长速率不受不同底物浓度的影响。氢气、二氧化碳（CO₂）、乙酸盐和乙醇是发酵的主要产物。检测到的其他重要终产物是甲酸盐和乳酸盐。在初始底物浓度较低导致细胞生长严重受限的培养物中，氢气产率为1摩尔氢气/摩尔葡萄糖。在因碳耗尽而生长停止的培养物中，乳酸盐和甲酸盐占总终产物的一小部分，在整个生长过程中，总终产物主要由氢气、二氧化碳、乙酸盐和乙醇组成。在初始底物浓度较高的培养物中，纤维二糖消耗不完全，细胞生长受到碳可用性以外的因素限制。即使在稳定期氢气仍持续产生，且氢气/二氧化碳比率始终大于1，在稳定期最高可达1.2。观察到最大比产氢速率为14.6毫摩尔·克干细胞⁻¹·小时⁻¹。当细胞进入稳定期时，在高底物浓度培养物中观察到细胞外丙酮酸的产生，乳酸盐成为主要终产物。
