Carbon and electron flow in Clostridium cellulolyticum grown in chemostat culture on synthetic medium
Carbon and electron flow in Clostridium cellulolyticum grown in chemostat culture on synthetic medium
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DOI：
10.1128/jb.181.10.3262-3269.1999
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发表时间：
1999-05-01
影响因子：
3.2
通讯作者：
Petitdemange, H
中科院分区：
文献类型：
--
作者：
Guedon, E;Payot, S;Petitdemange, H
先前的研究结果表明，在含有纤维素二糖和酵母提取物的培养基上培养溶纤维素梭菌时，其糖消耗较低，代谢和生长受到早期抑制。从复杂培养基到合成培养基的变化对：(1)比纤维素糖消耗量增加了三倍；（ii）电子流，因为在合成介质中NADH/NAD（+）比值从0.29到2.08不等，而在复杂介质中则高达42到57。这些数据表明，矿物盐介质比复杂介质对碳流的控制更好。通过连续培养，表明糖酵解产生的电子流被氢气、乙醇和乳酸盐的产生所平衡。在低碳流水平下，丙酮酸优先被裂解成醋酸酯和乙醇，使细菌能够最大限度地形成ATP。高分解代谢率导致丙酮酸溢出，乙醇和乳酸产量增加。体外条件下，甘油醛-3-磷酸脱氢酶、乳酸脱氢酶和乙醇脱氢酶水平较高，体内特定产率较高。氧化还原平衡主要由低碳流下的nadh -铁氧还蛋白还原酶-氢化酶维持，高碳流下的乙醇脱氢酶和乳酸脱氢酶维持。在无机盐和复合培养基中都发现了相同的最大生长速率（0.150 h(-1)），证明营养物质的吸收或生物合成前体的产生比它们的利用更快。在合成培养基中，纤维素二糖碳被转化为细胞团块并分解代谢产生ATP，而在复杂培养基中，它主要作为能量供应，如果过量存在，就会导致细胞内代谢物的积累，如NADH所示。在合成培养基和高水平的碳弓中生长的细胞能够诱导调节反应，如乙醇和乳酸脱氢酶的产生。
Previous results indicated poor sugar consumption and early inhibition of metabolism and growth when Clostridium cellulolyticum was cultured on medium containing cellobiose and yeast extract. Changing from complex medium to a synthetic medium had a strong effect on (i) the specific cellobiose consumption, which was increased threefold; and (ii) the electron flow, since the NADH/NAD(+) ratios ranged from 0.29 to 2.08 on synthetic medium whereas ratios as high as 42 to 57 on complex medium were observed. These data indicate a better control of the carbon flow on mineral salts medium than on complex medium. By continuous culture, it was shown that the electron flow from glycolysis was balanced by the production of hydrogen gas, ethanol, and lactate. At low levels of carbon flow, pyruvate was preferentially cleaved to acetate and ethanol, enabling the bacteria to maximize ATP formation. A high catabolic rate led to pyruvate overflow and to increased ethanol and lactate production. In vitro, glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and ethanol dehydrogenase levels were higher under conditions giving higher in vivo specific production rates. Redox balance is essentially maintained by NADH-ferredoxin reductase-hydrogenase at low levels of carbon flow and by ethanol dehydrogenase and lactate dehydrogenase at high levels of carbon flow. The same maximum growth rate (0.150 h(-1)) was found in both mineral salts and complex media, proving that the uptake of nutrients or the generation of biosynthetic precursors occurred faster than their utilization. On synthetic medium, cellobiose carbon was converted into cell mass and catabolized to produce ATP, while on complex medium, it served mainly as an energy supply and, if present in excess, led to an accumulation of intracellular metabolites as demonstrated for NADH. Cells grown on synthetic medium and at high levels of carbon Bow were able to induce regulatory responses such as the production of ethanol and lactate dehydrogenase.