INFLUENCE OF NUTRITIONAL FACTORS ON THE ANTIOXIDATIVE SYSTEM IN BACTERIA ISOLATED FROM BIOFILM

The 2,4-Dichlorophenoxyacetic acid (2,4-D) is a herbicide used in cereals, sugarcane and orchards, in the post-emergent control of weeds. However, it is also toxic to bacteria. Those microorganisms that are tolerant to herbicides, exhibit activity of some enzymes in the antioxidative process. The objective of this work was to evaluate enzymatic mechanisms of tolerance to herbicides and nutritional conditions. The Pseudomonas sp. strain was isolated from biofilm in the herbicide containers washing water reservoir and evaluated as 2,4-D tolerant. The rates of Hydrogen Peroxide (H2O2) and Malondealdehyde (MDA) were quantified as stress indicators; and Ascorbate Peroxidase (APX) and Glutathione Peroxidase (GPX) activities, such as antioxidative response system. Luria Broth (LB) and Mineral Medium (MM) with 2,4-D equivalent field concentration of 10x and 25x were used in the experiments, and three log phases was studied. In general, there was a better control of H2O2 rates in the terminal log phase, with the exception of LB25x, possibly related to the high growth rates in rich medium, and the toxic effect of the herbicide at this concentration. The MDA rates at terminal log follow a proportionality with H2O2 rates, possibly showing an increase in damage at LB25x. However, this proportionality does not occur at initial and median log phases, indicating that other mechanisms may be acting in the control of oxidative stress. The enzymes that act in the antioxidative process, APX and GPX, had approximately complementary activities in MM medium, indicating a control of the stress in all phases of log growth. The activities of both enzymes at LB treatments increased from the initial to the terminal log phase, but with exception for LB25x, which were presented relatively low. These results indicate a situation of oxidative stress in LB25x, characterized by the high production of H2O2, probably linked to the toxicity of high growth rates in the rich medium, late growing phase, and high 2,4-D concentration used in this treatment. The stress situation was also associated with the low activity of the antioxidative enzymes APX and GPX. In all remaining treatments, these enzymes were fundamental in response to the stress caused by the herbicide 2,4D in Pseudomonas sp. strain.