Singh Randeep, Yang Yea-Tyng, Lu Biqing, Bennett George N, San Ka-Yiu
Department of Bioengineering, Rice University, P.O. Box 1892, MS 142, Houston, Texas 77251-1892, USA.
Biotechnol Prog. 2006 May-Jun;22(3):898-902. doi: 10.1021/bp050326h.
Our laboratory previously studied the interaction between nuo and the acetate-producing pathway encoded by ackA-pta in Escherichia coli. We examined metabolic patterns, particularly the ethanol and acetate production rates, of several mutant strains grown under anaerobic growth conditions. Since the pyruvate formate-lyase (PFL) pathway is the major route for acetyl-CoA and formate production under anaerobic conditions, we examined the effects of nuo and ackA/pta mutations on the expression of pyruvate formate-lyase (pfl) under anaerobic conditions. The ackA-pta mutant has a pfl::lacZ expression level much higher than that of the wild-type strain, and cultures also exhibit the highest ethanol production. Real-time PCR demonstrated that the adhE gene expression in the ack-pta mutant strain was approximately 100 fold that of the same gene in the ackA-pta nuo mutant strain. This result correlates with the observed ethanol production rates in cultures of the strain. However, the lack of exact correlation between the ethanol production rates and the RT-PCR data suggests additional regulation actions at the posttranslation level. In addition, the activity of the pfl gene as indicated by mRNA levels was also considerably greater in theack-pta mutant. We can conclude that deletions of nuo and ack/pta can partially affect the expression of the genes encoding adhE and pfl under anaerobic conditions.
我们实验室之前研究了大肠杆菌中nuo与由ackA-pta编码的乙酸盐生成途径之间的相互作用。我们检测了几种突变菌株在厌氧生长条件下的代谢模式，尤其是乙醇和乙酸盐的生成速率。由于丙酮酸甲酸裂解酶（PFL）途径是厌氧条件下乙酰辅酶A和甲酸生成的主要途径，我们检测了nuo和ackA/pta突变对厌氧条件下丙酮酸甲酸裂解酶（pfl）表达的影响。ackA-pta突变体的pfl::lacZ表达水平远高于野生型菌株，其培养物的乙醇产量也最高。实时PCR表明，ack-pta突变菌株中adhE基因的表达量约为ackA-pta nuo突变菌株中同一基因表达量的100倍。这一结果与观察到的该菌株培养物中的乙醇生成速率相关。然而，乙醇生成速率与RT-PCR数据之间缺乏确切的相关性，这表明在翻译后水平存在额外的调控作用。此外，ack-pta突变体中pfl基因的活性（以mRNA水平表示）也显著更高。我们可以得出结论，在厌氧条件下，nuo和ack/pta的缺失可部分影响adhE和pfl编码基因的表达。
