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Alginate is a major component of brown algae, but it cannot be utilized for ethanol fermentation by industrial microorganisms. A natural alginate degrading and ethanol producing strain was obtained in our previous research. However, the research on the ethanol metabolism process of the natural alginate fermentation strain is lacked. In this research, the key enzyme and metabolic process of ethanol fermentation were studied. Three kinds of key enzyme including alginate lyase, pyruvate dehydrogenase and ethanol dehydrogenase were determined. The enzyme activity in the metabolic process was relatively high at 60-96 h which was the most important period during the fermentation. Meanwhile the concentration change of the important substances including soluble sugar, reducing sugar, acidity, pyruvic acid and ethanol were tracked and analyzed. Total soluble sugar and reducing sugar change tendency during the fermentation was similar. In the whole fermentation process, the fermentation broth was acidic. The value of pyruvic acid content reached highest at 72 h. During 48-96 h, the growth of ethanol concentration was very obvious. The alginate metabolic process in natural alginate fermentation strain was to generate extracellular alginate lyase to degrade alginate to produce reducing sugar, and then some intermediate metabolites formed such as pyruvic acid. Finally under the effect of pyruvate dehydrogenase and ethanol dehydrogenase, ethanol was produced.

The production of bioethanol from algae has attracted wide attention in the field of energy. A novel algae fermentation strain, Meyerozyma guilliermondii, can produce alginate lyase and alcohol dehydrogenase (ADH) at the same time. At present, there is no research on the fermentation conditions, separation, and purification of the alcohol dehydrogenase of Meyerozyma guilliermondii. In this research, the fermentation conditions of Meyerozyma guilliermondii, the separation, and purification processes of alcohol dehydrogenase, and the performance study of alcohol dehydrogenase were studied. According to the experimental results, the optimum fermentation conditions for enzyme production were as follows: fermentation medium with alginate, initial pH 5.0, and fermentation temperature of 30 °C. The highest enzyme activity reached 69.9 U mL-1 crude enzyme. The optimal treating time of the ultrasonic separation procedure was 12 min at power of 320 W. The suitable purification method of the enzyme was salting out and dialysis method. When saturation reached 50 %, the total enzyme activity was the highest. Finally, the properties of enzyme were studied in this research. The maximum activity was reached at pH 7. The optimum temperature of ADH activity was 35 °C.