Cell viability of <i>B</i>. <i>megaterium</i> isolates CCT 7729 and CCT 7730 after 3 h and 14 h of growth in MM, MMM and MMC media.

<p>Data were analyzed using two-way ANOVA followed by Bonferroni´s correction, *p < 0.05. The bars represent the standard errors on means.</p

Growth curve of the isolates (A) <i>B</i>. <i>megaterium</i> CCT 7729 and (B) <i>B</i>. <i>megaterium</i> CCT 7730.

<p>Legend: MM, MMM, and MMC indicate mineral medium, mineral medium with mesotrione, and mineral medium with Callisto, respectively. The bars represent the standard errors on means.</p

<i>Bacillus megaterium</i> strains derived from water and soil exhibit differential responses to the herbicide mesotrione

<div><p>The intense use of herbicides for weed control in agriculture causes selection pressure on soil microbiota and water ecosystems, possibly resulting in changes to microbial processes, such as biogeochemical cycles. These xenobiotics may increase the production of reactive oxygen species and consequently affect the survival of microorganisms, which need to develop strategies to adapt to these conditions and maintain their ecological functionality. This study analyzed the adaptive responses of bacterial isolates belonging to the same species, originating from two different environments (water and soil), and subjected to selection pressure by herbicides. The effects of herbicide Callisto and its active ingredient, mesotrione, induced different adaptation strategies on the cellular, enzymatic, and structural systems of two <i>Bacillus megaterium</i> isolates obtained from these environments. The lipid saturation patterns observed may have affected membrane permeability in response to this herbicide. Moreover, this may have led to different levels of responses involving superoxide dismutase and catalase activities, and enzyme polymorphisms. Due to these response systems, the strain isolated from water exhibited higher growth rates than did the soil strain, in evaluations made in oligotrophic culture media, which would be more like that found in semi-pristine aquatic environments. The influence of the intracellular oxidizing environments, which changed the mode of degradation of mesotrione in our experimental model and produced different metabolites, can also be observed in soil and water at sites related to agriculture. Since the different metabolites may present different levels of toxicity, we suggest that this fact should be considered in studies on the fate of agrochemicals in different environments.</p></div

Infrared spectrum profile of the lipid extract obtained after incubation on MM (Panel 1); MMM (Panel 2) and MMC (Panel 3) of <i>B</i>. <i>megaterium</i> CCT 7729, (A) 3 h, (B) 14 h and <i>B</i>. <i>megaterium</i> CCT 7730, (C) 3 h (D) 14 h (FTIR analysis with scans from 4,000 cm^-1 to 400 cm^-1).

<p>Bands 1 e 2 correspond to (CH₂); 3 to (CH₃₎; 4 to (C = O); 5 to (-C = C); 6 to (CH₂); 7 to (CH₃); 8 to (C-O) and to 9 (CH).</p

Graphical representation of the main results showing the different responses system to herbicides of <i>B</i>. <i>megaterium</i> CCT 7729 and CCT 7730.

<p>These strains were originated from water and soil environments contaminated with Callisto (A), respectively. The response system starts with different lipid saturation levels (B), forming a cascade characterized by different levels of membrane permeability and MDA rates (C), interfering with herbicide entry into the bacterial cells and inducing different antioxidant responses (D). Therefore, different levels of H₂O₂ between the two strains were created, originating distinct intracellular oxidizing environments (E) for each strain and, therefore, different degradation routes. These response systems interfered with the growth ability (F) and viability rates (G) and may be associated with the nutrient availability of the isolation environments of each strain (A). ↑ Represents significant increase compared with the control and ↓ represents significant decrease compared with the control.</p

CAT-PAGE of <i>B</i>. <i>megaterium</i> CCT 7729 (a) and <i>B</i>. <i>megaterium</i> CCT 7730 (b) after 3 and 14 h of growth in the control medium (MM) and treatment media (MMM and MMC).

<p>CAT-PAGE of <i>B</i>. <i>megaterium</i> CCT 7729 (a) and <i>B</i>. <i>megaterium</i> CCT 7730 (b) after 3 and 14 h of growth in the control medium (MM) and treatment media (MMM and MMC).</p

Characterization of the SOD isoforms in <i>B</i>. <i>megaterium</i> isolates CCT 7729 and CCT 7730.

<p>Characterization of the SOD isoforms in <i>B</i>. <i>megaterium</i> isolates CCT 7729 and CCT 7730.</p

(A) Quantification of H₂O₂ levels and (B) MDA in the <i>B</i>. <i>megaterium</i> isolates CCT 7729 and CCT 7730 after 3 h and 14 h periods in the MM, MMM, and MMC media.

<p>Data were analyzed using two-way ANOVA followed by Bonferroni’s correction, *p < 0.05. The bars represent the standard errors on means.</p

SOD-PAGE of samples from <i>B</i>. <i>megaterium</i> isolates CCT 7729 and CCT 7730 after 3 and 14 h of incubation in the control (MM) and treatment (MMM and MMC) media.

<p>SOD-PAGE of samples from <i>B</i>. <i>megaterium</i> isolates CCT 7729 and CCT 7730 after 3 and 14 h of incubation in the control (MM) and treatment (MMM and MMC) media.</p