The microbial degradation of nM-/uM concentrations of linuron estimated by a Lemna minor bioassay

摘要

In this work we studied the degradation of linuron by a microbial consortium (isolated from a linuron-treated orchard) and the strain Variovorax paradoxus, which is probably the main actor in this consortium. We used a plant-microbial bioassay, in which the aquatic macrophyte Lemna minor L. (duckweed) was used to monitor the biodegradation of linuron when this herbicide was applied to liquid cultures in nano- and micromolar concentrations. The toxicity of linuron to L. minor was assessed by several growth-related parameters such as total frond number, total frond area and doubling time. Log-logistic based dose-response analysis revealed significant growth inhibition of L. minor after 7 days of exposure to linuron concentrations > 80 nM. The relationship between herbicide dose and plant response was described most accurately by using an equation that is modified for growth stimulation at lower doses. The microbial consortium and the V. paradoxus strain significantly protected Lemna plants from the toxic effects of concentrations up to 1.28 mu M linuron. These results suggest that both inocula were capable of degrading nanomolar concentrations of linuron but there was indication that the consortium performed better than the pure isolate. In addition to the growth-related parameters, chlorophyll a fluorescence imaging was used to estimate the outcome of the plant-microbe-toxicant interaction by measuring the specific plant metabolic processes affected by linuron.