Exploiting plant-microbe partnerships to improve plant growth and phytoremediation

Abstract

Established methods to remediate contaminated soils and groundwater are frequently expensive, environmentally invasive, labour intensive, and do not make cost-effective use of existing resources. Especially in case of large-scale contaminated areas phytoremediation is considered to be a cost-effective and sustainable alternative for remediation since it works in situ, is solar powered and demands minimal site disturbance and maintenance. However, phytoremediation still has to deal with some important shortcomings like phytotoxicity, a limited contaminant uptake, and evapotranspiration of volatile organic contaminants. Plant-associated bacteria can be exploited to overcome these constraints. In case of phytoremediation of organic contaminants, endophytes equipped with the appropriate degradation pathway can diminish phytotoxicity and evapotranspiration. To increase metal bioavailability and to decrease metal phytotoxicity during phytoremediation of toxic metals, plantassociated bacteria that are provided with a metal resistance/sequestration system and that are capable of producing siderophores and/or organic acids can be used. Proof of this concept was already provided under controlled laboratory conditions for single contaminations of toluene or nickel. However, at most contaminated sites, plants and their associated microorganisms have to deal with mixed pollutions of organics and toxic metals. Moreover, this proof of concept on laboratory scale is no guarantee that (a) in situ inoculation of bacteria is possible, (b) the inoculated strains will become an integrated part of the endogenous community, and (c) the selection pressure will be sufficient to maintain a stable degradation capacity and/or metal sequestration. Since the main objective of this work was to move endophyte-enhanced phytoremediation towards application in the field, these critical issues were further investigated. ...