Cold-active microbial oxidoreductases from Arctic sea ice and the deep sea

Industrial biotechnology has become a key technology towards a bio-based economy, which is currently developed to face climate change, the growth of the human population and limited fossil resources (Soetaert & Vandamme, 2010). Especially the chemical industry has started to become “green” by applying biotechnological processes, which provide both ecological and economical benefits (Dale, 2003). However, the development of novel, environmentally friendly processes requires extensive academic and industrial research in different fields of science and process engineering. Furthermore, efficient processes can only be established by iterative optimization, e. g. to reduce by-product formation and waste streams (Schmid et al., 2001). A prominent example of a by-product, which needs valorization in order to improvethe efficiency of the process, is glycerol. Due to the increase in biodiesel production over the past decade, an excess of glycerol is currently produced. To diminish expenses for the disposal of crude glycerol and to gain value-added products from this low-cost substrate instead, sophisticated new biorefinery concepts will have to be developed (Almeida et al., 2012). The aim of this study was to identify biocatalysts for the conversion of glycerol and glycerol-derived substrates. To obtain unusual enzymes with potential for biotechnological applications, a screening of extremophiles had to be performed. The first task of this study was, therefore, to develop a high-throughput screening for the identification of cold-active oxidoreductases from psychrophilic microorganisms. In particular, two approaches were applied: an activity-based screening of psychrophilic wild-type strains, which had previously been isolated from Arctic sea ice, and a sequence-based screening of a metagenome database derived from a microbial deep-sea consortium. The second major task comprised cloning and expression of novel oxidoreductase encoding genes. Of the obtained recombinant enzymes, most promising candidates for future industrial applications were selected for purification and subsequent biochemical characterization.