A novel, high performance enzyme for starch liquefaction -: Discovery and optimization of a low pH, thermostable α-amylase

High throughput screening of microbial DNA libraries was used to identify alpha-amylases with phenotypic characteristics compatible with large scale corn wet milling process conditions. Single and multiorganism DNA libraries originating from various environments were targeted for activity and sequence-based screening approaches. After initial screening, 15 clones were designated as primary hits based upon activity at pH 4.5 or 95 degreesC without addition of endogenous Ca2+. After further characterization, three enzyme candidates were chosen each with an exceptional expression of one or more aspects of the necessary phenotype: temperature stability, pH optimum, lowered reliance on Ca2+ and/or enzyme rate. To combine the best aspects of the three phenotypes to optimize process compatibility, the natural gene homologues were used as a parental sequence set for gene reassembly. Approximately 21,000 chimeric daughter sequences were generated and subsets screened using a process-specific, high throughput activity assay. Gene reassembly resulted in numerous improved mutants with combined optimal phenotypes of expression, temperature stability, and pH optimum. After biochemical and process-specific characterization of these gene products, one a-amylase with exceptional process compatibility and economics was identified. This paper describes the synergistic approach of combining environmental discovery and laboratory evolution for identification and optimization of industrially important biocatalysts.