Characterization of a Thermostable, Recombinant Carboxylesterase from the Hyperthermophilic Archaeon Metallosphaera sedula DSM5348

Lipid-producing microalgae are emerging as the leading platform for producing alternative biofuels in response to diminishing petroleum reserves. Optimization of fatty acid production is required for efficient conversion of microalgal fatty acids into usable transportation fuels. Microbial lipases/esterases can be used to enhance fatty acid production because of their efficacy in catalyzing hydrolysis of esters into alcohols and fatty acids while minimizing the potential poisoning of catalysts needed in the biofuel production process. Although studies have extensively focused on lipases/esterases produced by mesophilic organisms, an understanding of lipases/esterases produced by thermophilic, acidic tolerant microbes, such as Metallosphaera sedula, is limited. In this work, the carboxylesterase from Metallosphaera sedula DSM5348 encoded by Msed_1072 was recombinantly expressed in Escherichia coli strain BL21 (λDE3). The purified enzyme either with a hexahistidine (His6)-tag (Msed_1072Nt and Msed_1072Ct) or without the hexahistidine (His6)-tag (Msed_1072) was biochemically characterized using a variety of substrates over a range of temperatures and pH and in the presence of metal ions, organic solvents, and detergents. In this study, the fusion of the protein with a hexahistidine (His6)-tag did not result in a change in substrate specificity, but the findings provide information on which enzyme variant can hydrolyze fatty acid esters in the presence of various chemicals, and this has important implication for their use in industrial processes. It also demonstrates that Metallosphaera sedula Msed_1072 can have application in microalgae-based biofuel production systems.