A novel thermophilic and halophilic esterase from Janibacter sp. R02, the first member of a new lipase family (Family XVII).

Janibacter sp. strain R02 (BNM 560) was isolated in our laboratory from an Antarctic soil sample. A remarkable trait of the strain was its high lipolytic activity, detected in Rhodamine-olive oil supplemented plates. Supernatants of Janibacter sp. R02 displayed superb activity on transesterification of acyl glycerols, thus being a good candidate for lipase prospection. Considering the lack of information concerning lipases of the genus Janibacter, we focused on the identification, cloning, expression and characterization of the extracellular lipases of this strain. By means of sequence alignment and clustering of consensus nucleotide sequences, a DNA fragment of 1272bp was amplified, cloned and expressed in E. coli. The resulting recombinant enzyme, named LipJ2, showed preference for short to medium chain-length substrates, and displayed maximum activity at 80°C and pH 8-9, being strongly activated by a mixture of Na and K. The enzyme presented an outstanding stability regarding both pH and temperature. Bioinformatics analysis of the amino acid sequence of LipJ2 revealed the presence of a consensus catalytic triad and a canonical pentapeptide. However, two additional rare motifs were found in LipJ2: an SXXL β-lactamase motif and two putative Y-type oxyanion holes (YAP). Although some of the previous features could allow assigning LipJ2 to the bacterial lipase families VIII or X, the phylogenetic analysis showed that LipJ2 clusters apart from other members of known lipase families, indicating that the newly isolated Janibacter esterase LipJ2 would be the first characterized member of a new family of bacterial lipases.