Metabolic flux in cellulose batch and cellulose-fed continuous cultures of Clostridium cellulolyticum in response to acidic environment
Metabolic flux in cellulose batch and cellulose-fed continuous cultures of Clostridium cellulolyticum in response to acidic environment
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DOI：
10.1099/00221287-147-6-1461
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发表时间：
2001-06-01
期刊：
影响因子：
2.8
通讯作者：
Petitdemange, H
中科院分区：
文献类型：
--
作者：
Desvaux, M;Guedon, E;Petitdemange, H
纤维素水解梭菌是一种非瘤胃纤维素水解中温细菌，在纤维素上使用化学定义的培养基进行批量和连续培养。与pH控制在7.2的培养相比，在不调节pH的批量培养中，纤维素降解较少，可溶性葡萄糖积累较多，可溶性葡萄糖积累较多。通过pH控制获得的纤维素降解的增益被分解代谢物的产生而不是可溶性糖生物量的积累所抵消。ph控制条件提高了生物质、乙醇和乙酸的产量。而乳酸和胞外丙酮酸的最大浓度低于非ph控制条件。在恒定稀释率和ph值范围从7.4到6.2的纤维素喂化恒温器中。pH 7.0时细胞密度最大。环境酸化主要影响生物量的形成。因为在pH 6.4时，细胞的干重比pH 7.0时低了四倍以上。而纤维素同化的比速率仅从11.74降低到10.13毫当量碳（g细胞）（-1）h（-1）。摩尔生长率和能量生长率不随ph的降低而下降，而是突然过渡到冲蚀。降低pH诱导从醋酸-乙醇发酵转变为乳酸-乙醇发酵。随着pH的降低，乙酸/乙醇的比值减小，在pH 6.4时接近1。不管pH值是多少。乳酸脱氢酶总是大量过剩。随着pH值的降低。丙酮酸-铁氧还蛋白氧化还原酶的生物合成效率和分解代谢效率均下降，其比酶活性与比代谢率之比从9.8下降到1.8。因此，仅1个pH单位的变化就会引起相当大的代谢变化，并在pH约6.2时以冲洗结束。溶纤维素菌对酸性条件的敏感性与瘤胃溶纤维素菌相似。显然，到目前为止研究的纤维素分解厌氧菌在pH值低于6.0时不会茁壮成长。这表明它们是在不需要酸耐受性来与其他微生物成功竞争的环境中进化的。
Clostridium cellulolyticum, a nonruminal cellulolytic mesophilic bacterium, was grown in batch and continuous cultures on cellulose using a chemically defined medium. In batch culture with unregulated pH, less cellulose degradation and higher accumulation of soluble glucides were obtained compared to a culture higher accumulation of soluble glucides were obtained compares to a culture with the pH controlled at 7.2. The gain in cellulose degradation achieved with pH control was offset by catabolite production rather than soluble sugar biomass accumulation. The pH-controlled condition improved biomass, ethanol and acetate production. whereas maximum lactate and extracellular pyruvate concentrations were lower than in the non-pH-controlled condition. In a cellulose-fed chemostat at constant dilution rate and ph values ranging from 7.4 to 6.2. maximum cell density was obtained at pH 7.0. Environmental acidification chiefly influenced biomass formation. since at pH 6.4 the dry weight of cells was more than fourfold lower compared to that at pH 7.0. whereas the specific rate of cellulose assimilation decreased only from 11.74 to 10.13 milliequivalents of carbon (g cells)(-1) h(-1). The molar growth yield and the energetic growth yield did not decline as ph was lowered, and an abrupt transition to washout was observed. Decreasing the pH induced a shift from an acetate-ethanol fermentation to a lactate-ethanol fermentation. The acetate/ethanol ratio decreased as the pH declined, reaching close to 1 at pH 6.4. Whatever the pH conditions. lactate dehydrogenase was always greatly in excess. As pH decreased. both the biosynthesis and the catabolic efficiency of the pyruvate-ferredoxin oxidoreductase declined, as indicated by the ratio of the specific enzyme activity to the specific metabolic rate, which fell from 9.8 to 1.8. Thus a change of only 1 pH unit induced considerable metabolic change and ended by washout at around pH 6.2. C. cellulolyticum appeared to be similar to rumen cellulolytic bacteria in its sensitivity to acidic conditions. Apparently, the cellulolytic anaerobes studied thus far do not thrive when the pH drops below 6.0. suggesting that they evolved in environments where acid tolerance was not required for successful competition with other microbes.