| dc.description.abstract | With the advances of industrial technology, the efficiency of agricultural production has been greatly improved. While satisfying human’s needs, the agriculture also comes along with large amounts of solid organic waste. For example, Taiwan′s agriculture produces 200,000 tons of fish waste and 130,000 tons of bagasse annually, respectively. In the past, the economic value added by organic waste recycling is low (such as compost), reducing the public’s will for organic waste recycling. Therefore, this study aims to valorize fish waste and bagasse to produce highly value-added products, and thereby enhancing the public’s will for organic waste recycling. α-Ketoisocaproic acid (KIC) is a naturally occurring metabolite of leucine that is capable of boosting animal muscle growth. In this study, we managed to develop a Bacillus-based fermentation system to produce KIC using fish waste and bagasse as the substrates. We selected Bacillus subtilis as the model organism for the KIC bioproduction because B. subtilis readily secrets extracellular protease subtilisin to the environments, which can hydrolyze fish waste protein into free amino acids. The leucine released would be subsequently converted into KIC by B. subtilis. We observed the optimal protein degradation rate in the wild-type B. subtilis cultures at pH 8.0 and at 40℃, and thus performing all the KIC bioproduction trials under such conditions. Later, we found that deletion of the bkdAB, which is responsible for KIC degradation, led to the KIC accumulation. In addition, heterologous expression of L-amino acid deaminase (LAAD) in B. subtilis increased the KIC yield up to 26 g/kg of fish waste. The results showed that the B. subtilis ∆bkdAB + LAAD cultures produced a 1.75 times higher yield of KIC (3.37 mmol per L of culture) than the yield of the B. subtilis ∆bkdAB culture. Moreover, we observed a higher amino acid utilization rate and a lower CO2 emission in B. subtilis ∆bkdAB + LAAD cultures compared to that in wild-type B. subtilis cultures. Altogether, this thesis demonstrated a successful microbial fermentation system capable of converting solid organic waste into the non-toxic, value-added products. This system represents an addition to circular bioeconomy, buttressing the 12th goal (responsible consumption and production) of the Sustainable Development Goals (SDGs) and facilitating the net-zero CO2 emission. | en_US |