BackgroundBiological methods of polycyclic aromatic hydrocarbons (PAH) contamination elimination typically involve the transformation of contaminants to non-toxic materials by microorganisms and plants and appear to be the most effective methods available.MethodsIn this study, Bacillus licheniformis and Bacillus mojavensis isolated from oil-contaminated soils were inoculated onto Festuca arundinacea seeds before planting in the pot and 3 weeks after planting by syringe injection into the rhizospheric zone in order to study the elimination of PAHs from Festuca’s rhizosphere in the greenhouse. Some physical and chemical properties of the soil, PAH concentrations, seeds germination percentage, root and shoot biomasses of the treated samples were examined.ResultsThe results showed that the treated samples inoculated with both bacteria had a significantly higher percentage of seed germination and root and shoot biomass compared to other treatments. The concentration of some PAHs reduced significantly (Pvalue < 0.05) in the rhizosphere of the treated samples inoculated with both bacteria compared to in contaminated soils. Concentrations of some PAHs (eg. Naphthalene, Phenanthrene, Benzo[a]anthracene and Dibenzo[a,h]anthracene) even reached below the detection limit of the method. The PAHs concentrations in the treated samples inoculated with bacteria was decreased significantly (Pvalue < 0.05). Therefore, the results showed the high efficiency of the Festuca and bacterial inoculation in eliminating PAHs from the soil.ConclusionAccording to the results, the partnership of Festuca with B. licheniformis and B. mojavensis isolates displayed positive effect on PAHs dissipation and can be effective cleanup technology with high performance.
The presence of toxic compounds like toluene has caused extensive contamination in oil-contaminated environments. Using bacteria to degrade monoaromatic compounds could be a good approach to finding a suitable bioaugmentation agent. In this study on toluene, degrading bacterial species were isolated from oil-contaminated environments (located in Bandar-Anzali, Guilan, Iran). The strain has been molecularly identified as Bacillus cereus ATHH39 (Accession number: KX344721) by partial sequencing of the 16S rDNA gene. Response surface methodology (RSM) was used for biodegradation of toluene by ATHH39 by implementing the central composite design (CCD). The central composite design (CCD) was applied to optimize and investigate pH, temperature, and toluene concentrations and their interactions for enhancing cell growth and toluene degradation by ATHH39 under in vitro conditions. The variables (pH, temperature, and toluene concentrations) with the highest significant impacts on growth and toluene degradation were selected. According to the prediction and optimization function of the design expert software, the optimum conditions of cell growth and toluene degradation were found. When pH, temperature, and toluene concentration were adjusted to 6.72, 33.16ºC and 824.15 mg/l, respectively, cell growth and toluene degradation reached OD 600 = 0.69 and 64.11%, respectively, which is very close to the predicted cell growth and toluene degradation of OD 600 = 0.71 and 65.85%, indicating that the response surface methodology optimization of process parameters for cell growth and toluene degradation is reliable. Based on the results, the ATHH39 strain was introduced as a useful microorganism with the potential for bioremediation of wastewater containing toluene.
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