In vitro protein synthesis is affected by the herbicide 2,4-dichlorophenoxyacetic acid in Azospirillum brasilense

Rhizobium leguminosarum bv. viciae 3841 Adapts to 2,4-Dichlorophenoxyacetic Acid with "Auxin-Like" Morphological Changes, Cell Envelope Remodeling and Upregulation of Central Metabolic Pathways

There is a growing need to characterize the effects of environmental stressors at the molecular level on model organisms with the ever increasing number and variety of anthropogenic chemical pollutants. The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), as one of the most widely applied pesticides in the world, is one such example. This herbicide is known to have non-targeted undesirable effects on humans, animals and soil microbes, but specific molecular targets at sublethal levels are unknown. In this study, we have used Rhizobium leguminosarum bv. viciae 3841 (Rlv) as a nitrogen fixing, beneficial model soil organism to characterize the effects of 2,4-D. Using metabolomics and advanced microscopy we determined specific target pathways in the Rlv metabolic network and consequent changes to its phenotype, surface ultrastructure, and physical properties during sublethal 2,4-D exposure. Auxin and 2,4-D, its structural analogue, showed common morphological changes in vitro which were similar to bacteroids isolated from plant nodules, implying that these changes are related to bacteroid differentiation required for nitrogen fixation. Rlv showed remarkable adaptation capabilities in response to the herbicide, with changes to integral pathways of cellular metabolism and the potential to assimilate 2,4-D with consequent changes to its physical and structural properties. This study identifies biomarkers of 2,4-D in Rlv and offers valuable insights into the mode-of-action of 2,4-D in soil bacteria.

Interactions of atrazine and 2,4-D with human serum albumin studied by gel and capillary electrophoresis, and FTIR spectroscopy

The herbicides 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine) and 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agricultural practice to fight dicotyledon weeds mainly in maize, cereals, and lucerne. As a result, these compounds are found not only in the plants, soil, and water, but also in the cultivated ground in the following years as well as in agricultural products such as fruits, milk, butter, and sugar beet. The toxicological effects of herbicides occur in vivo, when transported to the target organ through the bloodstream. It has been suggested that human serum albumin (HSA) serves as a carrier protein to transport 2,4-D to molecular targets. This study was designed to examine the interaction of atrazine and 2,4-D with HSA in aqueous solution at physiological pH with herbicide concentrations of 0.0001-1 mM, and final protein concentration of 1% w/v. Gel and capillary electrophoresis, UV-visible and Fourier transform infrared spectroscopic methods were used to determine the drug binding mode, the drug binding constant, and the protein secondary structure in aqueous solution. Structural analysis showed that different types of herbicide-HSA complexes are formed with stoichiometric ratios (drug/protein) of 3:1 and 11:1 for atrazine and 4.5:1 and 10:1 for 2,4-D complexes. Atrazine showed a weak binding affinity (K=3.50 x 10(4) M(-1)), whereas two bindings (K(1)=2.50 x 10(4) M(-1) and K(2)=8.0 x 10(3) M(-1)) were observed for 2,4-D complexes. The herbicide binding results in major protein secondary structural changes from that of the alpha-helix 55% to 45--39% and beta-sheet 22% to 24--32%, beta-anti 12% to 10--22% and turn 11% to 12--15%, in the drug-HSA complexes. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of herbicides in aqueous solution.

2,4-Dichlorophenoxyacetic acid affects the attachment of Azospirillum brasilense Cd to maize roots

2.4-Dichlorophenoxyacetic acid (2,4-D) is a herbicide widely applied to forage, grain and cereals. We previously determined that 1 mM 2,4-D diminished cell growth and cellular activity of Azospirillum brasilense Cd. The present work was designed to determine the possible effect of this herbicide--at concentrations used on crops--on the attachment of the bacteria to maize roots, since this step is of prime importance for the growth stimulation of the plant obtained with Azospirillum brasilense. In this paper we demonstrate that 2,4-D alters the bacterial adhesion to maize roots.

Characterization of 2,4-dichlorophenoxyacetic acid transport and its relationship with polyamines in Azospirillum brasilense

We have previously shown that 2,4-dichlorophenoxyacetic acid (2,4-D) inhibits Azospirillum brasilense growth, the synthesis of DNA, RNA and proteins. These toxic effects are prevented when polyamines are added to the culture medium. The purposes of our research were to determine the effects of the herbicide on the number of viable Azospirillum brasilense cells, characterize the 2,4-D transport system and to study the effects of polyamines upon the latter in this microorganism. We found that 2,4-D reduced the number of viable cells and that 2,4-D transport is energy-independent, since it was not affected by metabolic inhibitors. Polyamines did not alter 2,4-D uptake, further supporting the hypothesis that the herbicide most likely produces its toxic effects by interfering with the polyamine metabolism.

The interaction of 2,4-dichlorophenoxyacetic acid, ribosomes and polyamines in Azospirillum brasilense

2,4-Dichlorophenoxyacetic acid (2,4-D) is an herbicide used extensively in agriculture. We had previously determined that 1 mM 2,4-D could inhibit cell growth, DNA and protein synthesis of Azospirillum brasilense. The present work was designed to determine if these alterations are a consequence of 2,4-D action on polyamine biosynthesis and if the protein synthesis inhibition is a result of ribosomal impairment. In this paper we demonstrate that 2,4-D alters the metabolism of polyamines and, thus, affects protein synthesis at the ribosomal level.

Effects of 2,4-dichlorophenoxyacetic acid on Rhizobium sp. growth and characterization of its transport

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) produced a deleterious effect on the growth of Rhizobium sp. M4, that was reversed by transferring the cells to a fresh control medium. The uptake of 2,4-D by Rhizobium sp. was not affected by chloramphenicol, indicating that it is constitutive rather than inducible. The mechanism of transport also appears to be energy independent, since uptake was not inhibited by azide or arsenate.