Distribution of the Mycobacterium community and polycyclic aromatic hydrocarbons (PAHs) among different size fractions of a long‐term PAH‐contaminated soil

Abstract

Summary Mycobacterium is often isolated from polycyclic aromatic hydrocarbon (PAH)-contaminated soil as degraders of PAHs. In model systems, Mycobacterium shows attachment to the PAH substrate source, which is considered to be a particular adaptation to low bioavailability as it results into increased substrate flux to the degraders. To examine whether PAH-degrading Mycobacterium in real PAH-contaminated soils, in analogy with model systems, are preferentially associated with PAH-enriched soil particles, the distribution of PAHs, of the PAH-mineralizing capacity and of Mycobacterium over different fractions of a soil with an aged PAH contamination was investigated. The clay fraction contained the majority of the PAHs and showed immediate pyrene- and phenanthrene-mineralizing activity upon addition of (14)C-labelled pyrene or phenanthrene. In contrast, the sand and silt fractions showed a lag time of 15-26 h for phenanthrene and 3-6 days for pyrene mineralization. The maximum pyrene and phenanthrene mineralization rates of the clay fraction expressed per gram fraction were three to six times higher than those of the sand and silt fractions. Most-probable-number (MPN)-polymerase chain reaction demonstrated that Mycobacterium represented about 10% of the eubacteria in the clay fraction, while this was only about 0.1% in the sand and silt fractions, indicating accumulation of Mycobacterium in the PAH-enriched clay fraction. The Mycobacterium community composition in the clay fraction represented all dominant Mycobacterium populations of the bulk soil and included especially species related to Mycobacterium pyrenivorans, which was also recovered as one of the dominant species in the eubacterial communities of the bulk soil and the clay fraction. Moreover, Mycobacterium could be identified among the major culturable PAH-degrading populations in both the bulk soil and the clay fraction. The results demonstrate that PAH-degrading mycobacteria are mainly associated with the PAH-enriched clay fraction of the examined PAH-contaminated soil and hence, that also in the environmental setting of a PAH-contaminated soil, Mycobacterium might experience advantages connected to substrate source attachment.

Insight into the Modulation of Dissolved Organic Matter on Microbial Remediation of PAH-Contaminated Soils

“…And, the ratios of abundances of different PAH-degrading genes to bacterial 16S rRNA gene in some DOM-treated soils were significantly higher than that in the control on some incubation time. It indicated that addition of DOMs was an important driving force to stimulate the growth of bacteria especially those responsible for the [35][36][37][38]. The profiling analysis of microbial communities can contribute to identify the members of potential PAH-degrading microbial consortia and understand the patterns of microbial responses to external stimuli in polluted soils [14,39].…”

Importance of soil organic matter for the diversity of microorganisms involved in the degradation of organic pollutants

“…In contrast, cells of Rhodococcus or Cryptococcus would preferentially be located in less affected microsites, as it was the case for POM, sand or silt. Niche preference for clay within a soil matrix has, in fact, been demonstrated for a Mycobacterium degrading polycyclic aromatic hydrocarbons (Uyttebroek et al, 2006).…”

The reactive transport of trichloroethene is influenced by residence time and microbial numbers

“…The pH at the column effluent was regularly verified using pH-indicator strips (Universal indicator, Merck). DNA was extracted from 400 µL of liquid sample or 400 µg of wet solid phase as described by Uyttebroek et al (2006). Quantification of Dehalococcoides numbers was performed using real-time PCR as described previously (Dijk et al 2008) with a detection limit of 1.6×10 6 16S rDNA copies L -1 .…”