International Journal of Environmental Bioremediation & Biodegradation, 2017, Vol. 5, No. 1, 1-7 Available online at http://pubs.sciepub.com/ijebb/5/1/1 ©Science and Education Publishing DOI:10.12691/ijebb-5-1-1 Polyaromatic Hydrocarbon Phytoremediation Stimulated By Root Exudates John C. Thomas 1,* , Donald K. Russell 2 , Clayton L. Rugh 3 1 University of Michigan-Dearborn, Department of Natural Sciences, Dearborn, MI 2 Ford Motor Company, Environmental Quality Office, Ste. 950 West, Three Parklane Blvd., Dearborn 3 Michigan State University, Department of Crop and Soil Sciences, 516 Plant and Soil Science Bldg., East Lansing, Michigan *Corresponding author: jcthomas@umich.edu Abstract To encourage polyaromatic hydrocarbon (PAH) degradation in a historic steel production facility, contaminated soil was amended with 10% (v/v) compost and 5% (v/v) poultry litter. Within twelve 11.89 m X 27.13 m plots, 35,000 native Michigan perennials were planted. Soil and heterotrophic bacteria were sampled over several years beneath unplanted (control), Eupatorium perfoliatum (Boneset), Aster novae-angliae (New England Aster), Andropogon gerardii (Big Bluestem), and Scirpus atrovirens (Green Bulrush). All soils were found to degrade many PAHs, in one case up to 37% of the total. Cultivable microbes from the beneath plants were recovered, and 16S rDNA sequencing was used to identify microbial species. Implicated in phytoremediation, root exudates were prepared from select plants. Exudate amino acid composition changed with increasing plant age. A shift from Met and Lys to Glu and Asn was observed in exudates obtained from Swamp Goldenrod (Solidago patula). In Boneset, and New England Aster, Gly and Ala comprised at least 10% the total amino acids. Besides remediating a large fraction of the soil PAHs, the majority of planted plants survived the 3-year experiment. Root secretions and indigenous microbial communities may establish beneficial relationships that promote in situ PAH phytoremediation. Keywords: bioremediation, native plant species, environmental toxicity cleanup Cite This Article: John C. Thomas, Donald K. Russell, and Clayton L. Rugh, “Polyaromatic Hydrocarbon Phytoremediation Stimulated By Root Exudates.” International Journal of Environmental Bioremediation & Biodegradation, vol. 5, no. 1 (2017): 1-7. doi: 10.12691/ijebb-5-1-1. 1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants with cytotoxic, teratogenic and carcinogenic properties. PAHs with more than three aromatic rings are known as HMW PAHs. These toxicants are produced during the incomplete combustion of organic material through pyrolysis and pyrosynthesis, and are abundant in fossil fuels [1,2]. HMW PAHs are slightly soluble in water, are electrochemically stable and may be acutely toxic, putting at risk human and ecological health [3]. The physical and chemical properties of HMW PAHs contribute to their being persistent in the environment, in both their initial and chemically transformed forms [4]. Because of their high octanol–water partition coefficients (K ow ), HMW PAHs may predominate in organic phases in soil and sediments, and bioaccumulate [5]. In situ bioremediation may relieve the "cradle to grave" transition of raw materials flowing into manufactured goods, subsequently discarded in traditional landfills or on farmland [6]. Such pollutant dumping can be harmful to plants growing in those soils. Some fuel oils contain hydrocarbons that inhibit plant growth as well as seed germination [7]. PAHs and other organic pollutants derived from pesticides, coal or other fuel combustion, or from sewage may persist in soils and contaminate the plants grazed upon by livestock [8,9,10]. Poor plant growth noted in some contaminated soils can be attributed to acidification and nutrient depletion of soils. Using alder plants and root inoculation of N 2 -fixing bacteria such as Frankia and/or ectomycorrhizal fungi, mining waste soil pH was effectively adjusted to 7.5 [11]. Novosphingobium sp. are found in soils, and can effectively detoxify contaminants, greatly improving plant growth [12]. Nitrogen availability is also a key limitation for plant growth on contaminated sites. The addition of N-fertilizer was implicated in increasing sugars, sugar alcohols, and phenolics in root exudates, thereby enhancing the number and diversity of biodegrading rhizosphere bacteria [13]. Using select plants, soil detoxification with phytoremediation can lead to the subsequent introduction and growth of new plant and microbial species [14,15,16]. While some plant species secrete enzymes capable of transforming aromatic pollutants [17], it is widely believed plants more commonly stimulate changes in microbial populations and promote PAH metabolism in situ, [16,18,19,20]. Microbial population titer and composition all are thought to be potential targets affected by root exudates [20]. Laboratory studies have shown that roots release nutrients and organic compounds that may facilitate microbial growth and PAH biodegradation [15,17,21,22]. Exuded from plant roots, plant metabolites such as sugars, amino acids, phenolic and terpenoid compounds may all contribute to bacterial degradation of organic contaminants