Weilan Shao
Jiangsu University School of the Enviroment, China
Title: How does Thermoanaerobacter ethanolicus regulate its ethanol fermentation pathway?
Biography
Biography: Weilan Shao
Abstract
Thermoanaerobacter species can efficiently use lignocellulose derived substrates to grow at temperatures above 70°C. T. ethanolicus produces ethanol as main fermentation product. The final steps of the ethanol fermentation pathway are redox reactions from acetyl-CoA to ethanol via an acetaldehyde intermediate. AdhA, AdhB and AdhE encoded by genes adhA, adhB and adhE are the key aldehyde/alcohol dehydrogenases to catalyze these reactions. rnAafter identifying adhE in T.ethanolicus, we find that the ethanol titer of fermentation is controlled by both transcriptional regulation and the properties of AdhA, AdhB and AdhE. The transcription of dehydrogenase genes is regulated by redox sensing protein, which binds to oprators of different affinities so that adhA, adhB and adhE are expressed at directed time. Real time PCR results show that cells transcribe adhB in the absence of ethanol while the transcription of adhA and adhE needs be induced by a low concentration of ethanol. Further increased ethanol concentrations inhibit the transcription of all these genes. Under imitating physiological conditions, the enzyme AdhE and AdhB play crucial roles of aldehyde and alcohol dehydrogenases, respectively, in ethanol formation. However, the propertied and physiological roles of AdhA were not determined until the enzyme is successfully expressed and purified recently. The main physiological function of AdhA is to control ethanol titer by sensing and consuming ethanol in growing cells. After T. ethanolicus JW200 was transformed by adhA or/and adhE expression plasmids, the homologous expression of adhE enhenced the ethanol production, while that of adhA reduced the ethanol fermentation levels.rnThese results supports a regulation theory: The limitation of ethanol concentration during fermentation is caused by a systematic regulation through transcriptions and activities of the key enzymes in the ethanol-formation pathway.