Inactivation of aprE Gene in Bacillus subtilis 168 by Homologus Recombination

One of the most important producers of high quality industrial enzymes is the Gram-positive bacterium, Bacillus subtilis (B. Subtilis). One major limitation that hinders the wide application of B. subtilis is the secretion of high levels of extracellular proteases which degrade the secreted foreign proteins. In this study, homologus recombination technique was used to knock out its protease gene, aprE.

The internal segment of the pro-sequence of aprE gene of B. subtilis 168 with a length of 80 bps and its complementary sequence were synthesized and ligated into pUB110 at EcoR1 and XbaI restriction sites. Competent cells of B. subtilis 168 were prepared and transformed by electroporation using Bio Rad gene pulser as explained in the methods section. Transformants carrying the recombinant plasmid were selected for resistance to neomycin. The success of homologous recombination was checked by PCR amplification of the neomycin gene which was part of the vector and did not exist in the genome of B. subtilis 168. The protease activity was measured using the Protease Fluorescent Detection Kit based on the proteolytic hydrolysis of fluorescein isothiocyanate (FITC)-labeled casein-substrate.

The results demonstrated that aprE gene would not be able to produce further active subtilisin E. The reduction of protease activity also confirmed the efficacy of the induced mutation in this gene.

It will therefore be a major challenge for future research to identify and modulate quality control systems of B. subtilis which limit the production of high quality protease- sensitive products such as lipase.