Pseudomonas monteilii and Citrobacter murliniae, Biosurfactant-Producing Bacteria Isolated from Nigerian Soil

Aims: To isolate bacterial species with good potentials for biosurfactant production and to determine the tenso-active characteristics of the active producers.

Study Design: Study on biosurfactant-production potential of bacteria in shake flask.

Place and Duration of Study: Department of Applied Microbiology and Brewing, Nnamdi Azikiwe University, Awka, Nigeria, between October 2013 and June 2014.

Methodology: Soils, polluted with spent oil, from different regions of Anambra state, Nigeria, were examined for biosurfactant-producing bacteria. The bacterial isolates were screened for biosurfactant production in mineral salt medium (MSM) and nutrient broth supplemented with olive oil(NB). Biosurfactant production assay fermentation broth, include emulsification index measurement, oil displacement test, drop collapse test and blue agar plate test. The active producers were identified based on 16S rDNA sequencing.

Results: Out of the twenty-nine bacterial species screened, two of the isolates were recovered as active biosurfactant producers. They were identified as Pseudomonas monteilii AF064458 and Citrobacter murliniae AF025369. The biosurfactant production assay carried out on mineral salt medium and nutrient broth supplemented with olive oil revealed that P. monteilii AF064458 had emulsification index (E24) of 76.67% and 64.85%, oil displacement diameter of 2.1 cm and 1.2 cm respectively. The drop collapse test was positive in both medium and the organism showed a positive blue-agar plate test of 0.8 cm in diameter. With C. murliniae AF025369, an emulsification index (E24) of 66.67% and 63.33%, and an oil displacement diameter of 1.8 cm and 1.6 cm were obtained in MSM and NB respectively. A positive drop collapse test in both medium, and a negative blue-agar plate test were observed. Biosurfactants produced Biosurfactants produced by P. monteilii AF064458 and C. murliniae AF025369 reduced surface tension of water from 72 mN/m to 34 mN/m and 42 mN/m, with critical micelle concentrations (CMC) of 50 mg/L and 60 mg/L respectively.

Conclusion: The findings indicate that Pseudomonas monteilii AF064458 and Citrobacter murliniaeAF025369 are biosurfactant-producing bacteria.