Bench-Scale Production of Heterologous Proteins from Extremophiles- Escherichia coli and Pichia pastoris based expression systems

Abstract: Over the past few years considerable research attention has been assigned to extremophiles as sources of extremozymes due to their applicability in industrial processes, and the development of eco-friendly technologies. The establishment of efficient production strategies for heterologous proteins is an empirical process requiring broad background knowledge on available expression systems together with their major advantages and shortcomings. The studies conducted during the course of this thesis has included four enzymes originating from thermophiles namely, thermostable glycoside hydrolases, xylanase and cellulase from Rhodothermus marinus, cyclomaltodextrinase from Anoxybacillus flavithermus and a phospholipase from alkaliphilic Bacillus halodurans. Batch cultivation of R. marinus in the presence of xylan allowed low production of the native xylanase in sufficient amounts to probe cell-attachment studies by enzymatic and immunological techniques. Higher levels of the target proteins were achieved by intracellular and extracellular heterologous production using an Escherichia coli and Pichia pastoris based expression system respectively. The production of a functional enzyme is intimately related to the host's cellular machinery furthermore, as a prerequisite, the establishment of efficient bioprocess strategies is crucial for attaining optimum enzyme production yields. The results presented include bench-scale production strategies employing high cell density fed-batch cultivations with E. coli as a host. Also efficient extracellular production of thermostable xylanase and alkaliphilic phospholipase production using the methylotrophic yeast P. pastoris as a host is reported.