Moving towards sustainable & economical bioproducts: bioremediation of waste streams and improving product titers

Andre David Bergeron

In this thesis research work, various underutilized waste streams were targeted as precursors for bioproduct production. Attempts were made to address critical technology gaps that limit the commercialization of these bioproducts. This thesis is split into two parts, each of which describes a different study to achieve these goals. PART 1 addresses a limitation affecting the widespread use of anaerobic digestion (AD) for managing dairy manure: the lack of robust AD effluent treatment strategies. Using algae for nutrient recovery is a promising option, however the high levels of ammonia/ammonium found in dairy AD effluent are toxic to most algae and limit nutrient recovery efficiencies. Dilutions or additional pretreatments of AD effluent have been previously used to achieve high algal growth. This work sampled dairy AD effluent lagoons in order to find algal strains naturally growing in high total ammonia nitrogen (TAN) environments. A strain of C. vulgaris was isolated from a lagoon containing 1.03 g/L TAN. The ammonia tolerance of the identified strain was subsequently tested in synthetic medium. Robust algal productivities were obtained (407 mg/L/d) when grown in a medium containing 1 g/l total ammonia nitrogen (TAN), indicating that the strain is well suited for high ammonia environments such as AD effluent. PART 2 describes an effort to increase the yield of bioproducts through metabolic pathway engineering. A Yarrowia lipolytica strain previously developed for the conversion of glycerol into long chain dicarboxylic acids (LCDCA-16 and 18) was found to predominantly synthesize the byproduct citric acid. Two metabolic engineering strategies were therefore tested in this study in an attempt to increase LCDCA titers. The first strategy was to overexpress the first committed step of fatty acid (FA) biosynthesis, acetyl-CoA carboxylase. In addition, two heterologous acyl-ACP transacylase enzymes (acyl-ACP TE) were expressed to disrupt FA activation and subsequent FA storage, degradation, and feedback inhibition. Ultimately these strategies, neither independently nor in conjunction, significantly increased LCDCA titers. These results indicate that the native fatty acid re-activation pathways may need to be further disrupted in order to increase product titers.

Moving towards sustainable & economical bioproducts: bioremediation of waste streams and improving product titers

Files and links (1)

Abstract

Metrics

Details