Abstract
To develop effective bioremediation strategies, it is always important to explore autochthonous microbial community diversity using substrate-specific enrichment. The primary objective of this present study was to reveal the diversity of aerobic xylene-degrading bacteria at a legacy BTEX-contaminated site where xylene is the predominant contaminant, as well as to identify potential indigenous strains that could effectively degrade xylenes, in order to better understand the underlying facts about xylene degradation using a multi-omics approach. Henceforward, parallel aerobic microcosms were set up using different xylene isomers as the sole carbon source to investigate evolved bacterial communities using both culture-dependent and independent methods. Research outcome showed that the autochthonous community of this legacy BTEX-contaminated site has the capability to remove all of the xylene isomers from the environment aerobically employing different bacterial groups for different xylene isomers. Interestingly, polyphasic analysis of the enrichments disclose that the community composition of the o-xylene-degrading enrichment community was utterly distinct from that of the m- and p-xylene-degrading enrichments. Although in each of the enrichments Pseudomonas and Acidovorax were the dominant genera, in the case of o-xylene-degrading enrichment Rhodococcus was the main player. Among the isolates, two Hydogenophaga strains, belonging to the same genomic species, were obtained from p-xylene-degrading enrichment, substantially able to degrade aromatic hydrocarbons including xylene isomers aerobically. Comparative whole-genome analysis of the strains revealed different genomic adaptations to aromatic hydrocarbon degradation, providing an explanation on their different xylene isomer-degrading abilities.
Highlights
Xylene is one of the volatile organic compounds composed of a central benzene ring with two methyl groups attached as substituents, arranged in three various positions to create three distinct isomers: m-xylene, o-xylene, and p-xylene (Marshall and Rodgers 2008; Kandyala et al 2010; Yan and Zhou 2011)
Though the concentration of contaminants significantly decreased compared to the beginning of the contamination with time because of the autochthonous microbial community, the concentrations of some of the contaminants are still beyond the permissible limit according to Hungarian standards
Based on all above it can be concluded that the microbial community at the Siklos BTEX-contaminated site of Hungary has the metabolic potential to aerobically degrade all isomers of xylene
Summary
Xylene is one of the volatile organic compounds composed of a central benzene ring with two methyl groups attached as substituents, arranged in three various positions to create three distinct isomers: m-xylene, o-xylene, and p-xylene (Marshall and Rodgers 2008; Kandyala et al 2010; Yan and Zhou 2011). As a result of these different practices and procedures, the deposition of xylene in soil and groundwater can pose a tremendous challenge to soil and groundwater resources (Kao and Wang 2000; Kandyala et al 2010; Atlas and Hazen 2011; Das and Chandran 2011; Alrumman et al 2015). Because of their relatively high water solubility, this type of contamination was often treated as a considerable threat to the primary drinking water reserves. Since xylene has been reported as toxic to the liver, kidneys, and central nervous system, once it enters into the body by skin contact or inhalation, monitoring and removal of xylene from the environment have been regarded globally as a high priority (Kao and Wang 2000; Andreoni and Gianfreda 2007; Kandyala et al 2010; Atlas and Hazen 2011; Das and Chandran 2011)
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