Enhanced biodegradation of oily wastewater through nuclear irradiation mutation and statistical experimental methodology

Abstract

This study presents the improved biodegradation of crude oil in aqueous phase using mutant Dietzia sp. obtained by random mutagenesis of wild Dietzia sp. using 60 Co-γ irradiation. The mutants obtained were screened based on their degradation performance and the best mutant was selected for oil degradation optimization research. A four factor central composite design coupled with response surface methodology was applied to evaluate and optimize the important variables. A genetically stable mutant, designated as M22, was isolated and demonstrated significantly higher degradation efficiency (52.5%) of total petroleum hydrocarbons (TPHs) than the parental strain (28.2%) in liquid media after 14 days of incubation. Increased production of enzyme responsible for the degradation was achieved with the mutant species. Optimum conditions were determined to be pH 7.6, 0.20 g/L K 2 HPO 4 , 0.57 g/L NH 4 NO 3 , and 0.62 g/L yeast extract. Approximately 68.5% of TPH was experimentally degraded after 14 h of incubation under the optimum conditions, which agreed well with the model prediction. Gas chromatography-mass spectrum analysis showed that the mutant M22 could degrade a wide range of crude oil fractions, while optimization of culture conditions could be effective for increasing its strain's degrading ability.

Biodegradation of used engine oil by novel strains of Ochrobactrum anthropi HM-1 and Citrobacter freundii HM-2 isolated from oil-contaminated soil

“…A genetically stable mutant, designated as M22, was isolated and approved significantly higher degradation percentage (52.5 %) of total petroleum hydrocarbons (TPHs) than the wild strain (28.2 %) in liquid media after incubation for 14 days. This enhancement was ascribed to increase production of enzymes responsible for the degradation by the mutant strain (Duan et al 2015 ).

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Implications of microbial adaptation for the assessment of environmental persistence of chemicals

“…These irradiations can induce mutations by forming pyrimidine dimerization and cross-links in DNA, but mutations can also be induced by exposure to various physical (Duan et al, 2015) or chemical agents (Sekar, Sivaprakasam, & Mahadevan, 2009). However, even if an induced mutation leads to enhanced degradation of various pollutants, such as phenol (Sekar et al, 2009), azo dye (Joshi, Inamdar, Jadhav, & Govindwar, 2013), tannery soak liquor (Sekar et al, 2009) and oil (Chen, Yang, Huang, Zhang, & Ding, 2011;Duan et al, 2015), the randomness of the approach makes it difficult to use it in bioremediation applications or in biodegradation testing strategies. Moreover, these types of mutation and genotype evolution induced by external stress are complex and difficult to predict in natural environments.…”

“…Indeed, alteration of gene sequences by exposure to various physical or chemical agents, such as UV irradiation and nitrous acid, can lead to the enrichment of effective strains for biodegradation of chemicals. Phenolic compounds (Ju & Parales, 2011;Mao et al, 2015), oil (Chen et al, 2011;Duan et al, 2015), azo dyes (Kannappan Panchamoorthy Joshi et al, 2013) or polycyclic aromatic hydrocarbons (Sideri, Goyal, Di Nardo, Tsotsou, & Gilardi, 2013) are different mixtures or chemicals that have been degraded by different strains after different stress induced mutations. Due to their randomness, such mutations can also lead to the biodegradation of nontoxic and persistent chemicals, even in an environment that provides enough nutrients for the community (van der Meer, 2006).…”

“…Investigating the relationship between microbial adaptation and biodegradation will ultimately facilitate the design of more robust screening tests. Furthermore, directed microbial adaptation may also be a solution to improve bioremediation of recalcitrant chemicals (Duan, He, Li, & Li, 2015;Timmis & Pieper, 1999) in contaminated environments or in wastewater treatment plant. Important issues and terms that we will discuss are 1) the definition of adaptation, 2) role of exposure to environmental pollution in microbial adaptation, 3) experimental induction of adaptation, 4) mechanisms of adaptation relevant to biodegradation, and 5) integrating microbial adaptation in biodegradability testing approaches.…”