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Author: search.filters.author.Farías, Alejandro RubénSubject: search.filters.subject.biodegradation

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    Clomazone biodegradation in soil microcosms : evaluation of bioaugmentation and biostimulation with native bacteria from rice crop soils in Chaco, Argentina
    (Sociedad Argentina de Microbiología General, 2025-12-02) Cuadra, Pablo Nicolás; Farías, Alejandro Rubén; Echeverría, Macarena Celeste; Jorge, Nelly Lidia; Vullo, Diana Lia
    Clomazone (CMZ) is a selective pre and post emergence herbicide indicated for application in rice crops. Its incorrect use has been causing environmental problems, such as soil, groundwater and surface water persistent contamination. CMZ-resistant/tolerant native bacterial strains were previously isolated from rice crop soils in Las Palmas, Chaco, which were able to degrade this herbicide in batch cultures. The aim of this study was to evaluate CMZ biodegradation under controlled experiments in soil microcosms (MC) by bioaugmentation (the addition of specific microorganisms) and biostimulation (the addition of nutrients to increase microbial population activity) procedures. For this purpose, 30 MC were prepared by triplicates using 150 g of sterile and non-sterile rice crop soils under different treatments: control (non-treated MC), bioaugmentation, and a combination of bioaugmentation and biostimulation. The soil used exhibited a phosphorus deficit (8.4x10-4%), therefore biostimulated MC were designed by adding a stock solution of K2HPO4 1M to achieve the optimal C:N:P ratio of 100:10:1. For bioaugmented-MC, inocula consisted of strain G1 or a mixed culture of the isolates G1, H2, and H3, selected according to previous results. The MC were incubated at 30 °C and monitored for a period of 60 days. Bacterial growth was assessed by viable cell counts every 7 days, while CMZ concentration in soil was quantified by HPLC at regular intervals to determine CMZ removal. Results indicated that sterile soil control MC showed no detectable microbial growth until day 15, and CMZ concentration remained stable throughout the 60 days, confirming its abiotic stability under these conditions. In contrast, the other experimental conditions evidenced bacterial growth over time however no CMZ removal was registered in non sterile soil control MC. In G1 MC, G1 attained a maximum growth of 1×102 CFU/g soil at 14 days and of 1×103 CFU/g soil in P-supplemented MC, suggesting that P availability is a limiting factor. Furthermore, the G1-H3-H2-bioaugmented MC also achieved cell development of 1×103 CFU/g soil at 14 days, both with and without P-amendment indicating a greater intrinsic growth capacity of the consortium and a lesser dependence on external P supplementation. A clear predominance of isolate H2 was observed, followed by H3 and, to a lesser extent, G1, suggesting a dynamic of competition among the strains. Regarding the CMZ concentration analysis by HPLC, differentiated results were obtained: G1-MC did not show significant agrochemical degradation under any treatment condition. However, in the G1-H3-H2-MC a 14% CMZ removal was observed at 35 days without biostimulation, while in P-supplemented MC, the removal percentage increased to 26% at 35 days. These results suggest that the microbial consortium with P-amendment is effective in CMZ degradation in MC, being a factor to consider for the herbicide removal in polluted and productive soils.
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    Analysis of herbicide biodegradation by native bacteria isolated from rice crop soils in Chaco, Argentina
    (Sociedad Argentina de Microbiología General, 2024-12-10) Cuadra, Pablo Nicolás; Farías, Alejandro Rubén; Jorge, Nelly Lidia; Vullo, Diana Lia
    In Argentina, weed management in rice and other crops is often done with herbicides that persist in the soil for a long time. The incorrect and indiscriminate use of these agrochemicals has caused environmental problems, such as soil, groundwater and surface water contamination. Clomazone (CLM), an herbicide from the chemical group of oxazolidinones, is a selective pre- and post-emergence herbicide indicated for application in rice. Imazapyr and imazapic (IMR+IMC) are two herbicides that belong to the group of imidazolinones which interfere weed growth by inhibiting the action of the plant enzyme acetohydroxyacid synthase (AHAS). The objective of this work was to analyze the growth kinetics (GK) of bacterial strains isolated from rice crop soils with CLM and IMR+IMC as the only carbon source, and to analyze their biodegradation over time.
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    Selection of native bacteria from rice soils resistant to glyphosate, clomazone and Kifix, to be used as biodegrading agents
    (2022-10-28) Cuadra, Pablo Nicolás; Fontana, Gimena Lilián; Farías, Alejandro Rubén; Jorge, Nelly Lidia; Vullo, Diana Lia
    Rice is the main crop worldwide, covering about 11% of the planet’s arable land and constitutes a strategic component of the diet adopted for more than half of the world population. In Argentina, 3% of its production is in the Province of Chaco. Glyphosate, clomazone and kifix, are herbicides commonly used in rice crops for weed control, generating alterations in the soil ecosystem, and affecting the trophic chain. In this province, several studies reported poisoning cases in humans by herbicide applications, particularly in La Leonesa. Consequently, local producers requested assistance to find a prompt solution for this environmental concern. As demonstrated, the ability of certain soil bacteria to degrade these types of pollutants ensures an onsite detoxification process. For this reason, the objective of this work was to isolate native bacteria from soils of rice crops, resistant to a mixture of agrochemicals composed by the commercial formulates of glyphosate, clomazone and kifix, to be applied in biodegradation tests. The soils samples were taken from 3 areas of a field intended for rice cultivation, located in La Leonesa: 1. Virgin area without registered pesticide applications (ZA), 2. Area without applications for a decade (ZB), and 3. Crop area with continuous application of agrochemicals (ZC). As a first approach, counts of cultivable microorganisms were carried out in a traditional nutrient medium (PCA) and an oligotrophic medium (AS= soil agar) with and without pesticides (CP and SP respectively). Differences were detected both in number and in the diversity according to the sampling area, the composition of the medium and the presence of pesticides. In parallel, mixed cultures were obtained from soil suspensions in a saline broth (M9) with 0.5% m/v glucose and 1% v/v of the same herbicides, obtaining new isolates in M9 agar (AM9). As a result, 24 strains were selected and purified from AS-CP, PCA-CP and AM9. Toxicity was evaluated by exposing these isolates to increasing concentrations of herbicides in agar cultures, registering a greater growth inhibition in AS-CP with respect to PCA and AM9, probably related to pesticide interactions with medium components lowering the bioavailability. From these tests, 16 strains were selected according to their resistance to the highest concentrations of the mixture (from 0.25% in AS-CP to 15% in PCA-CP). Finally, resistance assays were performed in M9 broth supplemented with increasing concentrations of herbicides (1-20% v/v), detecting 9 strains capable of developing up to 15% v/v. In further studies, pesticide biodegradation by-products will be screened in cultures supernatants. Regarding that the agrochemical applications in crops will eventually not be discontinued, this work represents the first step to develop an alternative based on native bacteria bioinoculants for the future quality recovery of Chaco rice production soils.