Fine‐scale degrader community profiling over an aerobic/anaerobic redox gradient in a toluene‐contaminated aquifer

Abstract

Hydrocarbon contaminants in groundwater can be degraded by microbes under different redox settings, forming hot spots of degradation especially at the fringes of contaminant plumes. At a tar-oil-contaminated aquifer in Germany, it was previously shown that the distribution of anaerobic toluene degraders as traced via catabolic and ribosomal marker genes is highly correlated to zones of increased anaerobic degradation at the lower fringe of the plume. Here, we trace the respective distribution of aerobic toluene degraders over a fine-scale depth transect of sediments taken at the upper fringe of the plume and below, based on the analysis of 16S rRNA genes as well as catabolic markers in intervals of 3-10 cm. Well-defined small-scale distribution maxima of typical aerobic degrader lineages within the Pseudomonadaceae, Comamonadaceae and Burkholderiaceae are revealed over the redox gradient. An unexpected maximal abundance of 9.2 × 10⁶ toluene monooxygenase (tmoA) genes per g of sediment was detected in the strongly reduced plume core, and gene counts did not increase towards the more oxidized upper plume fringe. This may point towards unusual ecological controls of these yet unidentified aerobic degraders, and indicates that competitive niche partitioning between aerobic and anaerobic hydrocarbon degraders in the field is not yet fully understood. These findings demonstrate the potential of catabolic marker gene assays in elaborating the ecology of contaminant plumes, which is a prerequisite for developing integrated monitoring strategies for natural attenuation.

Organic contamination versus mineral properties: competing selective forces shaping bacterial community assembly in aquifer sediments

“…Earlier studies on sediments from the same sites showed a low variability within biological replicates and a high reproducibility of technical replicates with our T-RFLP protocol (Pilloni et al 2012). Moreover, key degrader populations identified match well with the findings from earlier studies (Winderl et al 2008, Anneser et al 2010, Larentis et al 2013). …”

“…(T-RF 130 bp), Desulfobulbaceae (T-RF 159 bp), and Desulfosporosinus spp. (T-RF 228 bp), that have been identified in previous studies at this site (Winderl et al 2008, Anneser et al 2010, Pilloni et al 2011, Larentis et al 2013 were most abundant. Moreover, their relative abundance did not differ significantly between TQ and mica (Fig.…”

“…1). Microbial community composition investigated in natural (mixed) aquifer sediments collected from different zones and depths of the respective aquifer has been studied in earlier work with respect to key contaminant degraders (Winderl et al 2008, Pilloni et al 2011, Larentis et al 2013), redox gradients (Anneser et al 2008, 2010, and sulfur cycling (Einsiedl et al 2015). Here, we specifically evaluate individual selective forces responsible for shaping sediment microbial community composition and biomass including organic contamination and water chemistry.…”

“…Data evaluation was performed as reported elsewhere (Pilloni et al 2012, Larentis et al 2013. Data from 454 pyrosequencing as conducted in previous studies at this site (Winderl et al 2008, Anneser et al 2010, Pilloni et al 2012, Larentis et al 2013 were used to assign the most common terminal restriction fragments (T-RFs) to specific taxonomic groups. Briefly, forward and reverse quality-trimmed pyrosequencing reads were assembled into short contigs (up to ~500 bp) using the software Seqman II (DNAStar).…”

“…4). More detailed information on the affiliation of T-RFs to specific bacterial lineages is provided in Pilloni et al (2012) and Larentis et al (2013). …”