Cloning, sequencing and expression in Escherichia coli of two Rhizobium sp. genes encoding haloalkanoate dehalogenases of opposite stereospecificity

Abstract

A 6.5-kb EcoRI fragment of genomic DNA from a Rhizobium sp. cloned into pUC19 was able to endow Escherichia coli K-12 with the novel ability to grow at the expense of 2-chloropropionic acid. Subcloning showed that this property was a consequence of two dehalogenases encoded on a 2.2-kb PstI fragment. Further subcloning of the PstI fragment led to two constructs that encoded, separately, dehalogenase activity that acted stereospecifically on D-2-chloropropionic acid and L-2-chloropropionic acid, respectively. The genes encoding these two stereospecific dehalogenases have been sequenced and shown to be separated by 177 bp of non-coding DNA. Expression of the dehalogenase genes involved the vector promoter, suggesting that the anticipated Rhizobium sp. regulatory sequences were not functional in E. coli. Comparison of the deduced amino acid sequences of the two dehalogenases (18% identity) indicated that there was no obvious evolutionary relationship between them. Nor was there any striking identity with any other 2-chloropropionic acid dehalogenase studied so far.