Abstract
Escherichia coli is a robust, easily adaptable and culturable bacterium in vitro, and a model bacterium for studying the impact of xenobiotics in the environment. We have used correlative atomic force – laser scanning confocal microscopy (AFM-LSCM) to characterize the mechanisms of cellular response to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). One of the most extensively used herbicides world-wide, 2,4-D is known to cause hazardous effects in diverse non-target organisms. Sub-lethal concentrations of 2,4-D caused DNA damage in E. coli WM1074 during short exposure periods which increased significantly over time. In response to 2,4-D, FtsZ and FtsA relocalized within seconds, coinciding with the complete inhibition of cell septation and cell elongation. Exposure to 2,4-D also resulted in increased activation of the SOS response. Changes to cell division were accompanied by concomitant changes to surface roughness, elasticity and adhesion in a time-dependent manner. This is the first study describing the mechanistic details of 2,4-D at sub-lethal levels in bacteria. Our study suggests that 2,4-D arrests E. coli cell division within seconds after exposure by disrupting the divisome complex, facilitated by dissipation of membrane potential. Over longer exposures, 2,4-D causes filamentation as a result of an SOS response to oxidative stress induced DNA damage.
Highlights
A global crisis is emerging in which an increase in food demand which has led to the significant use and development of pesticides
Based on cytological evidence we propose that 2,4-D alters membrane potential, immediately impacting FtsZ, FtsA localization and disrupting cell division, induces oxidative DNA damage and initiates the SOS response, leading to the filamentous phenotype at longer exposure times
The minimum inhibitory concentrations (MIC) of 2,4-D for all strains used in this study were determined to be 6 mM, so 4 mM was used as the highest sub-lethal concentration that produced consistent and sufficient cell growth for microscopy and biochemical assays
Summary
A global crisis is emerging in which an increase in food demand which has led to the significant use and development of pesticides. Since the early 1940s, the herbicide 2,4-dichlorophenoxyacetic acid has been one of the most commonly used pesticides in Canada and world-wide to target broad-leaf weeds This compound persists with a half- life of 10–200 days in the environment and is known to have undesired effects on diverse species in the food chain, from mammals to soil bacteria (Boivin et al, 2005; Chinalia et al, 2007). 2,4-D Disrupts E. coli Cell Division exposure levels have been determined to be 5 mg kg−1, bacteria are exposed to a wide-range of pesticide concentrations depending on a number of factors such as soil type, moisture content, amount of organic matter and the presence of degrading bacteria (Zabaloy et al, 2010) This herbicide is known to have significant non-target effects and its complete mode of action is not clearly known, even in target species. Despite the significant application of this herbicide, its specific effects on non-target species are unknown
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