Gene Discovery in Antarctic Dry Valley Soils

Abstract

The metagenomic approach to gene discovery circumvents conventional gene and gene product acquisition by exploiting the uncultured majority of microorganisms in the environment. It was demonstrated in this study that metagenomic methods are suitable for gene mining in extreme environments that harbor very high levels of unculturable microorganisms. DNA was extracted from Antarctic mineral soil samples taken from the Miers Valley, Antarctica. The metagenomic DNA was also used to construct a fosmid library comprising over 7900 clones with an average insert size of 29 kb. PCR amplification using bacterial and archaeal 16S rRNA gene specific primers and subsequent denaturing gradient gel electrophoresis (DGGE) of bacterial 16S rDNA amplicons showed that a small percentage of bacterial diversity was captured in the metagenomic fosmid library. Activity-based screening for lipase and esterase genes using a tributyrin plate assay yielded twelve positive clones. LD1, a putative, novel cold-active GDSL lipase/esterase was identified and sequenced. The C-terminal domain of the ORF was found to be an autotransporter similar to those associated with type V secretion systems in Gram negative bacteria. Sub-cloning of the gene resulted in lipolytic activity in E. coli. Preliminary enzyme assays have determined that LD1 hydrolyses p-nitrophenyl esters with chain lengths shorter than C10, an indication that the enzyme is an esterase. Complete purification and characterisation of this enzyme is subject to further study.