Abstract
Microbial community composition and diversity at a diesel-contaminated railway site were investigated by pyrosequencing of bacterial and archaeal 16S rRNA gene fragments to understand the interrelationships among microbial community composition, pollution level, and soil geochemical and physical properties. To this end, 26 soil samples from four matrix types with various geochemical characteristics and contaminant concentrations were investigated. The presence of diesel contamination significantly impacted microbial community composition and diversity, regardless of the soil matrix type. Clean samples showed higher diversity than contaminated samples (
P
< 0.001). Bacterial phyla with high relative abundances in all samples included
Proteobacteria
,
Firmicutes
,
Actinobacteria
,
Acidobacteria
, and
Chloroflexi
. High relative abundances of
Archaea
, specifically of the phylum
Euryarchaeota
, were observed in contaminated samples. Redundancy analysis indicated that increased relative abundances of the phyla
Chloroflexi
,
Firmicutes
, and
Euryarchaeota
correlated with the presence of contamination. Shifts in the chemical composition of diesel constituents across the site and the abundance of specific operational taxonomic units (OTUs; defined using a 97% sequence identity threshold) in contaminated samples together suggest that natural attenuation of contamination has occurred. OTUs with sequence similarity to strictly anaerobic
Anaerolineae
within the
Chloroflexi
, as well as to
Methanosaeta
of the phylum
Euryarchaeota
, were detected.
Anaerolineae
and
Methanosaeta
are known to be associated with anaerobic degradation of oil-related compounds; therefore, their presence suggests that natural attenuation has occurred under anoxic conditions. This research underscores the usefulness of next-generation sequencing techniques both to understand the ecological impact of contamination and to identify potential molecular proxies for detection of natural attenuation.