科研之友
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摘要
The use of the phenoxy herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been steadily increasing in recent years due to its selectivity against broad-leafed weeds and use on genetically modified crops resistant to 2,4-D. This increases the likelihood of 2,4-D persisting in agriculturally impacted soils, sediments, and aquatic systems. Aerobic microorganisms are capable of degrading 2,4-D enzymatically. Anaerobic degradation also occurs, though the enzymatic pathway is unclear. Iron-reducing bacteria (FeRB) have been hypothesized to augment anaerobic degradation through the production of a chemically reactive Fe(II) adsorbed to Fe(III) oxyhydroxides. To test whether this iron species can catalyze abiotic degradation of 2,4-D, an enrichment culture (BLA1) containing a photosynthetic Fe(II)-oxidizing bacterium (FeOB) "Candidatus Chlorobium masyuteum" and the FeRB "Candidatus Pseudopelobacter ferreus", both of which lacked known 2,4-D degradation genes was investigated. BLA1 produces Fe(II)-adsorbed to Fe(III) oxyhydroxides during alternating photoautotrophic iron oxidation and dark iron reduction (amended with acetate) cycles. No 2,4-D degradation occurred during iron oxidation by FeOB Ca. C. masyuteum or during iron reduction by FeRB Ca. P. ferreus under any incubation conditions tested (i.e., +/-Fe(II), +/-cells, and +/-light), or due to the presence of Fe(II) adsorbed to Fe(III) oxyhydroxides. Our results cast doubt on the hypothesis that the mineral-bound Fe(II) species augments the anaerobic degradation of 2,4-D in anoxic soils and waters by iron-cycling bacteria, and further justify the need to identify the genetic underpinnings of anaerobic 2,4-D degradation. @@@ 2,4-D use has steadily increased due to genetically modified crops.Biological and chemical degradation pathways are not well understood in anaerobic organisms.An Fe-oxidizing and Fe-reducing bacterial co-culture did not degrade 2,4-D in biotic or abiotic 2,4-D degradation.No chemical degradation of 2,4-D by Fe during microbial Fe-cycling was detected in co-culture experiments.
