A complete catalase-encoding gene, designated soiCat1, was obtained from soil samples via metagenomic sequencing, assembly, and gene prediction. soiCat1 showed 73% identity to a catalase-encoding gene of Mucilaginibacter rubeus strain P1, and the amino acid sequence of soiCAT1 showed 99% similarity to the catalase of a psychrophilic bacterium, Pedobacter cryoconitis. soiCAT1 was identified as a psychrophilic enzyme due to the low optimum temperature predicted by the deep learning model Preoptem, which was subsequently validated through analysis of enzymatic properties. Experimental results showed that soiCAT1 has a very narrow range of optimum temperature, with maximal specific activity occurring at the lowest test temperature (4?°C) and decreasing with increasing reaction temperature from 4 to 50?°C. To rationally design soiCAT1 with an improved temperature range, soiCAT1 was engineered through site-directed mutagenesis based on molecular evolution data analyzed through position-specific amino acid possibility calculation. Compared with the wild type, one mutant, soiCAT1, exhibited an extended range of optimum temperature ranging from 4 to 20?°C. The strategies used in this study may shed light on the mining of genes of interest and rational design of desirable proteins. KEY POINTS: ? Numerous putative catalases were mined from soil samples via metagenomics. ? A complete sequence encoding a psychrophilic catalase was obtained. ? A mutant psychrophilic catalase with an extended range of optimum temperature was engineered through site-directed mutagenesis.