Biotechnological prospects of Thermoanaerobacter AK15; end-product formation from sugars, amino acids, lignocellulosic and macroalgae hydrolysates

Abstract

The present study is on the biotechnological potential of Thermoanaerobacter strain AK15 concerning its ability to produce ethanol and valuable alcohols from carbohydrates and amino acids as well as investigations on their enzyme capability. The strain AK15 was found to be positive for alkaline phosphate, C4 esterase, acid phosphatase, napthol-AS-BI-phosophohydrolase, and α-glucosidase. Strain AK15 is highly ethanologenic, producing a maximum of 1.57 mol ethanol per mol of glucose degraded at high liquid-gas phase ratios. The strain degrades most of the sugars tested as well as starch and pretreated hydrolysates of biopolymers (Whatman paper, newspaper, Timothy grass, Rhubarb leaves, and several macroalgae species) to ethanol mainly. The strains degraded serine and threonine when used as a single substrate, producing mainly acetate and ethanol as end products, and the branched-chain amino acids (leucine, isoleucine, valine) when cultivated in the presence of thiosulfate. The main end products from branched-chain amino acids were a mixture of their corresponding branched-chain fatty acids and alcohols. Finally, the strain was also shown to use butyrate as an electron sink during glucose degradation resulting in the reduced product butanol in addition to end products produced from glucose. Thus, strain AK15 is a promising candidate for ethanol and fine chemical production.