Cloning and nucleotide sequence of the isoamylase gene from a strain of Pseudomonas sp.

A strain of Pseudomonas sp., SMP1, isolated from a soil sample collected in the Monterotondo area (Rome), secreted isoamylase activity into the culture medium. The enzyme was purified and optimal reaction and stability conditions were determined by varying pH and temperature. The chemico-physical properties of the enzyme were similar to those of the isoamylase purified in Japan more than 20 years ago from 'Pseudomonas amyloderamosa' strain SB15. A genomic library of SMP1 was prepared in Escherichia coli using pUC12 as vector. Two isoamylase-producing colonies were identified out of 6300 screened. The hybrid plasmids isolated from the two clones showed common restriction patterns. The chromosomal portion of one of these plasmids (pSM257) was completely sequenced. Comparison between the deduced amino acid sequence of the isoamylase and the published sequences of other amylolytic enzymes showed the presence of conserved domains.