Molecular characterization of alkaline protease-coding gene from Bacillus licheniformis MK90 mutants with biofilm inhibitory activity

Abstract

Background Enzymes are organic materials that accelerate biochemical processes without themselves undergoing change. They can be produced by plant, animal, fungi, and bacteria. Bacterial proteases are much favorable than any other sources, because bacteria can grow quickly and can be easily cultivated in laboratory. Objective To isolate and screen bacteria from soil samples for their ability to produce alkaline protease, and to improve the alkaline protease production followed by evaluation of its antimicrobials and antibiofilm activity. Materials and methods Sample collection was carried out from different locations in Egypt. Isolation of bacteria from soil samples was done using serial dilution method on skim milk agar. All isolated bacteria were screened for their ability to produce protease enzyme. The bacterial isolate showing maximum alkaline protease activity was identified using 16 S rRNA genetic identification. To induce mutations, ultraviolet (UV) irradiation was used. The most active mutant strains were selected for production, purification, and characterization of alkaline protease followed by evaluation of alkaline protease antimicrobial and antibiofilm activity. Results and conclusion Three UV mutants (MT2, MT4, and MT26) out of 48 displayed proteolytic activity more than other mutants and wild type (WT). Bacillus alkaline extracellular protease gene was genetically characterized through isolation of the genomic DNA of Bacillus licheniformis MK90 WT, and the best protease-producing UV mutants were followed by amplification, sequencing, and analyses. WT strain and best protease-producing mutants were compared at proteomic level through sodium dodecyl sulfate polyacrylamide gel electrophoresis for total cellular proteins. Then protease enzyme of WT and mutants was purified and characterized. This study reports that the B. licheniformis protease was active at an alkaline pH and wide range of temperatures (40–60°C), reflecting its potential application in detergent and laundry industries. On the contrary, the antibiofilm activity of the protease enzymes was evaluated toward four pathogenic bacterial strains, i.e., Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Bacillus subtilis, and the results showed that proteases from B. licheniformis MK90 may be useful for controlling biofilm formation by some pathogenic bacteria.