Enhanced Phenanthrene Biodegradation in Soil by Slender Oat Root Exudates and Root Debris

Abstract

To investigate the mechanisms by which slender oat (Avena barbata Pott ex Link) enhances phenanthrene biodegradation, we analyzed the impacts of root exudates and root debris on phenanthrene biodegradation and degrader community dynamics. Accelerated phenanthrene biodegradation rates occurred in soils amended with slender oat root exudates as well as combined root debris + root exudate as compared with unamended controls. Root exudates significantly enhanced phenanthrene biodegradation in rhizosphere soils, either by increasing contaminant bioavailability and/or increasing microbial population size and activity. A modified most probable number (MPN) method was used to determine quantitative shifts in heterotrophic and phenanthrene degrader communities. During the first 4 to 6 d of treatment, heterotrophic populations increased in all amended soils. Both root debris-amended and exudate-amended soil then maintained larger phenanthrene degrader populations than in control soils later in the experiment after much of the phenanthrene had been utilized. Thus, root amendments had a greater impact over time on phenanthrene degraders than heterotrophs resulting in selective maintenance of degrader populations in amended soils compared with controls.

Microbial expression profiles in the rhizosphere of willows depend on soil contamination

“…One of the most interesting features of phytoremediation is that many plant-derived chemicals (root degradation compounds, secondary metabolites, etc.) stimulate microorganisms to degrade contaminants (Donnelly et al, 1994;Fletcher and Hegde, 1995;Haby and Crowley, 1996;Miya and Firestone, 2001;Isidorov and Jdanova, 2002). Many of these plant-derived compounds are PAH analogs (Singer et al, 2003), and the rhizosphere of plants growing in uncontaminated soils is already enriched in PAH-degrading microorganisms (Daane et al, 2001).…”

Influences of artificial root exudate components on the behaviors of BDE-28 and BDE-47 in soils: desorption, availability, and biodegradation

“…Root exudates are likely to stimulate soil microbial diversity and activity and thereby facilitate microbial biodegradation of organic contaminants. Both in vivo and in vitro experiments have demonstrated that root exudates can enhance microbial biodegradation of petroleum hydrocarbons in soils (Miya and Firestone 2001;Joner et al 2002;Corgié et al 2004Corgié et al , 2006. Research by Yoshitomi and Shann (2001) has shown that root exudates stimulate microbial mineralization of polycyclic aromatic hydrocarbons (PAHs) by the growth of soil microorganisms and the changes in structure and function of microbial community.…”

Root Exudation: The Ecological Driver of Hydrocarbon Rhizoremediation

“…Root exudation is now considered to be the most important factor in the mediation of hydrocarbon biodegradation in the rhizosphere [54, 67,104,141,[227][228][229][230][231][232]. Root exudates serve as a carbon source and energy for microorganisms, and also improve the hydrocarbon degradation in the rhizosphere by stimulating hydrocarbon-degrader populations [67].…”

“…Increasing the microbial biomass and activity by exudation of labile C and N can be a solution. For example, the addition of root debris to phenanthrene contaminated soils only improve phenanthrene degradation after 20 days, in contrast to more labile water soluble exudates, which reflects the low biodegradability of the root debris [231]. In contrast, the high solubility of low molecular weight exudates allows them a higher mobility in soil and a rapid uptake by microbial cells [54].…”