Screening, cloning and expression of a novel alginate lyase gene from P. aeruginosa TAG 48 and its antibiofilm effects on P. aeruginosa biofilm

Pseudomonas aeruginosa is an opportunistic pathogen and utilizes several virulence factors for pathogenesis. One of the most important factors is alginate, found in the biofilm which enables P. aeruginosa to establish chronic lung infections.In this study, 25 clinical alginate-degrading isolates were selected. Biochemical and molecular approach were carried out to identify the isolates by 16S rDNA gene amplification. Growth conditions and enzyme production were the criteria for selection. Since the main objective of the project was the production and characterization of alginate lyase and its effect on biofilm elimination, the P. aeruginosa sp.TAG48 alginate lyase-encoding gene was isolated, cloned, sequenced and expressed in E.coli DH5α. The resultant enzyme was purified by affinity chromatography. Ciprofloxacin, tobramycin and cefixime were also used to test the effectiveness of these antibiotics on P. aeruginosa biofilm by minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC). The synergistic effects of these antibiotics and the recombinant alginate lyase on biofilm were evaluated.Results indicate that the addition of alginate (0.2%–0.8%) and NaCl (0.2–0.5 M) to the medium significantly increases cell growth followed by higher enzyme production (p≤ 0.05). Moreover, substrate specificity of alginate lyase produced by P. aeruginosa sp.TAG48 shows the enzyme is capable of degrading both polyM and polyG alginate and acts bifunctionally. Results from the antimicrobial characteristics of the antibiotics and the enzyme have shown MBIC for ciprofloxacin, tobramycin, cefixime and enzyme in the following concentrations 4, 32, 256 and 18.75 μg/ml, and MBEC: 32, 128, ≥ 512 and 37.5 μg/ml, respectively. The study of synergism between the antibiotics and the enzyme to prevent growth and eradication of P. aeruginosa sp.TAG48 biofilm shows that alginate lyase exhibits synergy with tobramycin and cefixime but not with ciprofloxacin.The results indicate that the use of purified novel alginate lyase with antibiotics could be a beneficial alternative for the treatment of P. aeruginosa infections. Elucidation of mechanisms involved in antibiotic resistance and the role of biofilm structure could assist physicians select optimum treatment regimen.