Mechanisms of phytoremediation: biochemical and ecological interactions between plants and bacteria

Abstract

The use of plants to reduce contaminant levels in soil is a cost-effective method of reducing the risk to human and ecosystem health posed by contaminated soil sites. This review concentrates on plant-bacteria interactions that increase the degradation of hazardous organic compounds in soil. Plants and bacteria can form specific associations in which the plant provides the bacteria with a specific carbon source that induces the bacteria to reduce the phytotoxicity of the contaminated soil. Alternatively, plants and bacteria can form nonspecific associations in which normal plant processes stimulate the microbial community, which in the course of normal metabolic activity degrades contaminants in soil. Plants can provide carbon substrates and nutrients, as well as increase contaminant solubility. These biochemical mechanisms increase the degradative activity of bacteria associated with plant roots. In return, bacteria can augment the degradative capacity of plants or reduce the phytotoxicity of the contaminated soil. However, the specificity of the plant-bacteria interaction is dependent upon soil conditions, which can alter contaminant bioavailability, root exudate composition, and nutrient levels. In addition, the metabolic requirements for contaminant degradation may also dictate the form of the plant-bacteria interaction i.e., specific or nonspecific. No systematic framework that can predict plant-bacteria interactions in a contaminated soil has emerged, but it appears that the development of plant-bacteria associations that degrade contaminants in soil may be related to the presence of allelopathic chemicals in the rhizosphere. Therefore, investigations into plants that are resistant to or produce allelopathic chemicals is suggested as one possible method of identifying plant-bacteria associations that can degrade contaminants in soil.Résumé : L'utilisation des plantes pour réduire les teneurs en contaminants des sols est une méthode coûteuse pour réduire les risques envers la santé de l'homme et des écosystèmes occasionnés par la présence de sols contaminés. Dans leur revue, les auteurs concentrent leur attention sur les interactions plantes-bactéries qui augmentent la dégradation des composés organiques problématiques du sol. Les plantes et les bactéries peuvent former des associations spécifiques dans lesquelles les plantes fournissent aux bactéries une source spécifique de carbone qui amène ces bactéries à réduire la phytotoxicité du sol contaminé. Alternativement, les plantes et les bactéries peuvent former des associations non spécifiques dans lesquelles les processus végétaux normaux stimulent la communauté microbienne, laquelle, au cours de ses activités métaboliques normales, dégrade les contaminants du sol. Les plantes fournissent des substrats carbonés et des nutriments et augmentent la solubilité des contaminants. Ces mécanismes biochimiques augmentent l'activité de dégradation des bactéries associées aux racines des plantes. En retour, les bactéries peuvent augmenter la capacité de dégradation de...

Efficiency of Rye Biomass on Oil Hydrocarbon Biodegradation

“…The main plant enzymes involved in degradation and detoxification of organic pollutants, including petroleum products, belong to oxidoreductase class. It is established that a large proportion of these enzymes found in plant root exudates distinction along with the other metabolites [14]. Extra cellular plant enzymes including laccases, dehalogenases, nitroreductases, peroxidases and hydrolases can be effective against a number of contaminants.…”

“…The microbe number intensively increased in soil with hexadecane, and achieved log7 CFU/1g. Aside from the uptake of compounds with subsequent metabolism, plants frequently participate indirectly by changing the soil conditions so that soil micro-organisms can degrade pollutants [14]. Plants affect the water balance, pH of a site, and stimulate microbial activity of the soil.…”

Phytoremediation of Weathered Petroleum in Groundwater by Arroyo Willows in Nutrient Amended On-Site Mesocosms

“…As much as 40% of a plant's photosynthate can be deposited in the soil as root exudates (Kumar et al, 2006). A few known root exudates are similar in chemical structure to known pollutants as seen in Figure 2.5 (Siciliano and Germida, 1998).…”

“…Research by Stotz et al (2000) suggests that some of the exudates are actually a signal compound for either a symbiotic or a defense communication. (Siciliano and Germida, 1998) The Rhizosphere Effect: The successful application of rhizodegradation is largely dependent on promoting plant growth and supporting microbes to efficiently colonize the rhizosphere (Lugtenberg et al, 2001). This enhancement of the microbial activity that may enhance degradation of contaminants in the rhizosphere is called the rhizosphere effect (Frick et al, 1999).…”

“…The soluble plant products of alcohols, sugars, etc and root turnover accounts for 7-27% of the total plant mass produced annually and can account for 10% to 40% of plant photosynthesis output annually (Kamath et al, 2004;Kumar et al, 2006). The microbial population of the rhizosphere has been reported to be 4 to 100 times larger than that of the bulk soil, since the higher availability of organic matter is thought to support these high populations (Siciliano and Germida, 1998;Penrose and Glick, 2001). The composition of the microbial community is dependent on the plant species and the root exudates (Kirk et al, 2005).…”