Effects of PAH-Contaminated Soil on Rhizosphere Microbial Communities

Abstract

Bacterial associations with plant roots are thought to contribute to the success of phytoremediation. We tested the effect of addition of a polycyclic aromatic hydrocarbon contaminated soil on the structure of the rhizosphere microbial communities of wheat (Triticum aestivum), lettuce (Lactuca sativa var. Tango), zucchini (Cucurbita pepo spp. pepo var. Black Beauty), and pumpkin (C. pepo spp. pepo var. Howden) 16S rDNA terminal restriction fragment length polymorphism (T-RFLP) profiles of rhizosphere microbial communities from different soil/plant combinations were compared with a pairwise Pearson correlation coefficient. Rhizosphere microbial communities of zucchini and pumpkin grown in the media amended with highest degree of contaminated soil clustered separately, whereas communities of these plants grown in unamended or amended with lower concentrations of contaminated soil, grouped in a second cluster. Lettuce communities grouped similarly to cucurbits communities, whereas wheat communities did not display an obvious clustering. The variability of 16S rDNAT-RFLP profiles among the different plant/soil treatments were mostly due to the difference in relative abundance rather than presence/ absence of T-RFLP fragments. Our results suggest that in highly contaminated soils, the rhizosphere microbial community structure is governed more by the degree of contamination rather than the plant host type.

Rhizosphere effect on removal and bioavailability of PAHs in contaminated agricultural soil

“…Several plants were reported in PAH rhizoremediation assays (Sipila et al 2008;Pritchina et al 2011;Bisht et al 2014;Liu et al 2014;Salehi et al 2015;Shahsavari et al 2015), among which ryegrass has been chosen as a research target due mainly to its large and fibrous root system that enables it to colonize a large area of soil and favors interactions between roots, microbes and pollutants (Joner et al 2001;Corgi'e et al 2006;Xu et al 2014;Chen et al 2016). The influence of plants on PAHs dissipation may vary according to the distance from growing roots (Bourceret et al 2015), and it seems that PAH removal efficiency gets higher when proximity to roots increases (Corgi'e et al 2003).…”

Diversity and distribution of 16S rRNA and phenol monooxygenase genes in the rhizosphere and endophytic bacteria isolated from PAH-contaminated sites

“…The community structures of rhizosphere bacteria in heavy metal- or pesticide-contaminated environments have been investigated 19 20 21 . Pritchina et al 22 used a terminal restriction fragment length polymorphism (TRFLP) technique to investigate the rhizosphere bacterial communities of four types of plant grown in the presence of different PAH-contaminated soils; the results showed that the level of PAH pollution had a more significant influence on the rhizosphere bacterial community structure than did the type of host plant. Rhizosphere width (distance from root surface) also affected the bacterial species and quantities 23 .…”

“…Monooxygenase plays an important role in microbial biodegradation of PAHs 25 . The phenol monooxygenase (PHE) gene and several other aromatic oxygenase genes (e.g., toluene/naphthalene/chlorobenzene dioxygenase and ring hydroxylating monooxygenases) are typically used as indicator genes because of their substrate specificity, high conservation, and being the rate-limiting component in aromatic hydrocarbon biodegradation 22 26 27 28 . Therefore, investigations of PAH-degrading genes as well as the diversity and distribution of rhizospheric and endophytic bacteria in PAH-contaminated sites is particularly important; this is also a prerequisite for use of PAH-degradable bacteria to eliminate soil PAH contamination and reduce plant PAH risk.…”