Biodegradation of phthalate esters by Bacillus sp. And Pseudomonas sp. Isolated from soil

Abstract

Phthalate esters have been widely used not only as a plasticizer for polymer industries, but also used in the production of paint, glue, lubricant, pharmaceutics, cosmetics and pesticides. Due to a high demand, millions of tons have been globally produced per year. Consequently, they may leak into the environment from manufacturing, product use/disposal, industrial and municipal wastewater treatment plants and also be leached out of landfills causing a threat to aquatic environment. Since phthalate esters may result in carcinogenic, teratogenic and endocrine effects, degradation is therefore necessary. Recent studies have reported that short chain phthalate esters can be degraded either by hydrolysis or photolysis or by microorganisms. In this study, Bacillus sp. strain 3C3 which was isolated from hot spring soil in Krabi province, Thailand, as an organic-solvent tolerant bacterium and Pseudomonas aeruginosa strain DB-9 which was isolated from soil with a history of municipal waste exposure exhibited the ability to biodegrade a wide range of PEs, i.e. DMP, DEP, DPrP, DBP and BBP. The effect of additional carbon and energy source, temperature, pH, surfactant, PEs concentration and PEs interaction towards PEs biodegradation by Bacillus sp. strain 3c3 and P. aeruginosa strain DB-9 were investigated. Initially, Bacillus sp. strain 3C3 was able to slowly degrade DEP (0.45 mM) to the maximum at 68% within 2 days. The addition of yeast extract stimulated bacterial growth and enhanced the highest DEP biodegradability by 40%. Furthermore, bacterial growth rate and BBP degradation efficiency of P. aeruginosa strain DB-9 in the presence of yeast extract was increased by 25% and 2%, respectively. The optimal conditions for PEs degradation of Bacillus sp. strain 3c3 and P. aeruginosa strain DB-9 were at room temperature (35-37 °C) and pH 7.0. Tween 80 at 2 g L-1 was nonionic surfactant selected for enhancing PEs solubility and supporting bacterial growth of the strain DB-9, though it was slightly toxic to the strain 3c3. Moreover, Bacillus sp. strain 3c3 exhibited ability to completely degrade PEs at various concentrations, but the degradation capacity was decreased at higher concentrations. The P. aeruginosa strain DB-9 could completely degrade DBP and BBP at various concentrations, while DMP, DEP and DPrP could be degraded to some extents. In addition, the ability of Bacillus sp. strain 3c3 and P. aeruginosa strain DB-9 to degrade PEs in mixed conditions was also feasible.