Effcieny of bosurfactant from bacllus sp. GY19 enhancement of pyrene solublizaton and bodegradation

Abstract

The purpose of this study was to investigate efficiency of Bacillus sp. GY19 and its biosurfactant on enhancing of pyrene bioavailability and biodegradation. Firstly, six biosurfactant-producing bacterial screened strains were examined for efficiency of biosurfactant production by using several substrates as carbon source. Bacillus sp. GY19 was selected based on five criteria including; surface tension reduction of culture media (29 mN/m), emulsification activity with crude oil and diesel oil (56% and 64%, respectively), high biomass (1.8 g/l), capability to use bottom glycerol as carbon source and the highest crude oil solubilization property of cultivated broth by using bottom glycerol as carbon source (2,062 mg/l). Further study showed that cell-free broth containing biosurfactant of GY19 exhibited the property to solubilize naphthalene, acenaphthene, phenanthrene, fluoranthene and pyrene at 247, 41, 40, 12.6 and 3.6 mg/l, respectively. However, strain GY19 exhibited low ability to degrade 100 mg/l of phenanthrene, fluoranthene, pyrene and 0.5% (v/v) of crude oil and could not grow and produce biosurfactant in liquid media. Moreover, the GY19 cells also exhibited low adherence (3.5%) to hexadecane as measured by the BATH assay. Crude biosurfactant extracted by liquid-liquid extraction was therefore used in the studying on enhancement of pyrene biodegradation. The increasing concentration of crude biosurfactant resulted in high solubilization capability of PAHs in which 5 g/l of crude biosurfactant exhibited the highest solubilization of phenanthrene, fluoranthene and pyrene with 174, 449 and 522 mg/l, respectively. However, concentration at 5 g/l of crude biosurfactant exhibited toxicity to Pseudoxanthomonas sp. RN402 and Novosphingobium sp. PCY which were used as pyrene-degrading bacteria in this study. Hence, concentration at 1 g/l (above CMC) of crude biosurfactant was applied for enhancing pyrene degradation by strain RN402 and strain PCY in liquid medium. In enhancing pyrene biodegradation by crude biosurfactant experiment, the toxicity of crude biosurfactant mainly inhibited pyrene degradation for strain RN402 and strain PCY in form of free cells. On the other hand, immobilization of strain RN402 exhibited positive result at 500 mg/l of pyrene degradation while crude biosurfactant still exhibited toxicity to immobilized strain RN402. In conclusion, biosurfactant from Bacillus sp. strain GY19 using bottom glycerol as carbon source also exhibited high solubilization of PAHs and crude oil. However, it should be studied on other concentrations of crude biosurfactant on enhancing PAHs bioavailability and biodegradation. Furthermore, solubilization process can be further studied for applying in industrial as a detergent for cleaning oil or combining solubilization-biodegradation process to eliminate PAHs and crude oil.