Isolation and Characterisation of Biosurfactant-producing Pseudomonas specie from Soil

Abstract

Bacteria, especially members of the genera Bacillus and pseudomonads express surface-active compounds that are useful in biotechnology. Studies have shown that biosurfactant-expressing strains are rapidly isolated from both soil and water environments that are either contaminated or uncontaminated. The aim of this research is to isolate a large collection of surfactants expressing pseudomonads and to screen and characterised them for biosurfactant production. In this study, bacterial strains were isolated from Dundee Botanic Garden (United Kingdom) soil using pseudomonas selection agar supplemented with centrimide, fusidin and cephaloridine media (PSA+CFC) that select only pseudomonads. The isolates where screened for liquid surface tension reducing ability (LSTRA) using the drop-collapse assay before characterising the key strains using different metabolic and growth-based assays including their antibiogram. At least 30 key strains were identified from a collection of 58 isolated strains and further studied for diversity. A total of 27 assays were conducted to ascertain the phenotype of the 30 keys strains. All the 30 strains (100%) tested positive for catalase and glucose utilisation, while 28 (93%) tested positive for oxidase and KB* broth culture acidity. Also 22 (73%), 26 (87%) and 18 (60%) were found to be positive for swarming, swimming and twitching motilities respectively, while 22 (73%) were positive for lipase, 26 (87%) for protease and 27 (90%) for gelatinase. Furthermore, 12 (40%), 2 (7%), and 9 (30%) were resistance to mercury, kanamycin and to nalidixic acid respectively. Hierarchical cluster analysis of phenotypic characterisation data confirmed that these strains were a diverse group of pseudomonads.