Studies revealing bioremediation potential of the strain Burkholderia sp. GB-01 for abamectin contaminated soils

Dissipation, processing factors and dietary risk assessment of the bioinsecticide abamectin in herbal plants belonging to Lamiaceae family from open field to herbal tea infusion

Abamectin, the mixture of avermectin B1a and B1b, is widely used as a bioinsecticide and is an alternative to chemical pest control from insects. To our knowledge, its behaviour is not fully recognized, especially in herbs. Thus, the objective of this study was to investigate the environmental fate of abamectin in herbal plants belonging to the Lamiaceae family, its dissipation in open field studies laboratory processing treatments and dietary risk assessment. Three medicinally and culinary important species of herbs: Melissa officinalis L., Mentha × piperita L. and Salvia L. were treated with single and double dose than recommended on the label during their cultivation (BBCH 11-29). Residues were monitored using the QuEChERS method followed by the LC-MS/MS. The dissipation pattern of the sum of avermectin B1a and B1b and their persistence were observed 14 d after spraying. Abamectin decline was very rapid in plants and followed the first-order kinetics model. The half-life (t1/2) was in the range of 0.96-1.08 d (single dose) and 0.93-1.02 d (double dose). The pre-harvest intervals (decrease to the level of 0.01 mg kg-1) were 7.29-7.92 d at single and 7.99-8.64 d at double dose application. Herbal infusion preparation in previously washed and dried mint, lemon balm and sage leaves was the key processing step in the removal of abamectin residues. The reduction of initial deposits after single dose treatment was noted up to 65% (PF = 0.35-0.67) and up to 79% after double dose application (PF = 0.21-0.72) in herbal tea. Acute risk assessment of children and adults for the highest residues in EFSA PRIMo model at single and double dose expressed as hazard quotients (HQ) were <1, indicating no risk to humans via consumption of the herbal products. The data provide a better understanding of abamectin behaviour in herbal plants and can help assure herbs' safety for consumers.

Effect of soil fumigants on degradation of abamectin and their combination synergistic effect to root-knot nematode

BACKGROUND

Root-knot nematode (Meloidogyne spp., RKN) causes a disease that significantly reduces the yield of greenhouse cucumber crops year after year. Chemical control based on a single pesticide is now unreliable mainly due to pest resistance. Fumigant and non-fumigant pesticide combinations can potentially result in effective and economic RKN control.

RESULTS

Combining the insecticide abamectin (ABM) with fumigants dazomet (DZ) or chloropicrin (CP) significantly extended the half-life of ABM by an average of about 1.68 and 1.56 times respectively in laboratory trials, and by an average of about 2.02 and 1.69 times respectively in greenhouse trials. Laboratory experiments indicated that all the low rate ABM combination treatments controlled RKN through a synergistic effect. ABM diffused into the nematode epidermis more rapidly when ABM was combined with DZ and CP, giving effective nematode control and an increase cucumber total yield, compared to the use of these products alone. ABM combined with CP or DZ produced significantly higher total cucumber yield than when these products were used alone.

CONCLUSIONS

A low concentration of ABM combined with DZ in preference to CP would be an economic and practical way to control nematode and soilborne fungi in a greenhouse producing cucumbers.

Study of the degradation in aqueous solution of a refractory organic compound: avermectin type used as pesticide in agriculture

We examined the removal of abamectin by the electro-Fenton (EF) process and the feasibility of biological treatment after degradation. The effect of the operating parameters showed that abamectin (Aba) degradation was enhanced with increasing temperature. Response surface analysis of the central composite design led to the following optimal conditions for the abatement of chemical oxygen demand: 45.5 °C, 5 mg L^-1, 150 mA, and 0.15 mmol L^-1 for the temperature, initial Aba concentration, current intensity, and catalyst concentration, respectively. Under these conditions, 68.01% of the organic matter was removed and 94% of Aba was degraded after 5 h and 20 min of electrolysis, respectively. A biodegradability test, which was performed on a solution electrolyzed at 47 °C, 9 mg L^-1, 150 mA, and 0.15 mmol L^-1, confirms that the ratio of biological oxygen demand/chemical oxygen demand increased appreciably from 0.0584 to 0.64 after 5 h of electrolysis. This increased ratio is slightly above the limit of biodegradability (0.4). These results show the relevance of the EF process and its effectiveness for abamectin degradation. We conclude that biological treatment can be combined with the EF process for total mineralization.

Eco-toxicological effects of the avermectin family with a focus on abamectin and ivermectin

Avermectin family members are categorised as highly effective but toxic natural products that are used as pharmaceuticals in both humans and animals and for crop protection. Abamectin and ivermectin are the two most commonly used compounds from this family with abamectin the only compound to be used for both crop protection and pharmaceutical purposes. Avermectins are produced by the soil dwelling actinomycetes Streptomyces avermitilis and despite having complex chemical structures, they are manufactured via synthesis in large scales for commercial use. Although the extent of the eco-toxicological effects of avermectins is not well documented, reports of eco-toxicity exist. Avermectins have short half-lives and their residues can be eliminated through different food processing methods. However, avermectins can persist in water, sediment, soil and food products and therefore management practices that reduce the potential risks associated with eco-toxicity of these highly toxic compounds need to be further developed. This manuscript provides a critical review of the eco-toxicological risks and the potential for food contamination associated with avermectin use.

Abamectin in soils: Analytical methods, kinetics, sorption and dissipation

Abamectin is a broad-spectrum antiparasitic agent that has been widely employed in veterinary medicine and has also been used as a pesticide in agriculture. Veterinary drugs may reach the soil and may be transported to surface and ground waters, posing risks to terrestrial and aquatic organisms. Sorption, transformation and transport processes are primarily responsible for the fate of these substances in the environment. In this study, the sorption and the aerobic dissipation of abamectin in Brazilian soils (sand, clay and sandy-clay) were evaluated. For sorption studies, batch equilibrium experiments were performed. Sorption and desorption isotherms were fitted to the Freundlich model. Abamectin showed a high affinity to soil particles, with Freundlich sorption and desorption coefficients ranging from 44 to 138 μg(1-1/n) (cm(3))(1/n) g(-1) and from 89 to 236 μg(1-1/n) (cm(3))(1/n) g(-1), respectively. Dissipation of abamectin was evaluated in sterile and non-sterile soils in an aerobic and dark environment under controlled temperature and humidity. The time required for a 50% reduction of the amount of abamectin present in non-sterile soils was up to 4 days, and the time period for 90% dissipation was up to 12 days. In sterilized soils, there was no reduction in the concentration of abamectin over 37 days of exposure, suggesting that aerobic microbial degradation must have been the primary mechanism responsible for the dissipation of abamectin in soils.

Shifts in taxonomic and functional microbial diversity with agriculture: How fragile is the Brazilian Cerrado?

BACKGROUND

The Cerrado--an edaphic type of savannah--comprises the second largest biome of the Brazilian territory and is the main area for grain production in the country, but information about the impact of land conversion to agriculture on microbial diversity is still scarce. We used a shotgun metagenomic approach to compare undisturbed (native) soil and soils cropped for 23 years with soybean/maize under conservation tillage--"no-till" (NT)--and conventional tillage (CT) systems in the Cerrado biome.

RESULTS

Soil management and fertilizer inputs with the introduction of agriculture improved chemical properties, but decreased soil macroporosity and microbial biomass of carbon and nitrogen. Principal coordinates analyses confirmed different taxonomic and functional profiles for each treatment. There was predominance of the Bacteria domain, especially the phylum Proteobacteria, with higher numbers of sequences in the NT and CT treatments; Archaea and Viruses also had lower numbers of sequences in the undisturbed soil. Within the Alphaproteobacteria, there was dominance of Rhizobiales and of the genus Bradyrhizobium in the NT and CT systems, attributed to massive inoculation of soybean, and also of Burkholderiales. In contrast, Rhizobium, Azospirillum, Xanthomonas, Pseudomonas and Acidobacterium predominated in the native Cerrado. More Eukaryota, especially of the phylum Ascomycota were detected in the NT. The functional analysis revealed lower numbers of sequences in the five dominant categories for the CT system, whereas the undisturbed Cerrado presented higher abundance.

CONCLUSION

High impact of agriculture in taxonomic and functional microbial diversity in the biome Cerrado was confirmed. Functional diversity was not necessarily associated with taxonomic diversity, as the less conservationist treatment (CT) presented increased taxonomic sequences and reduced functional profiles, indicating a strategy to try to maintain soil functioning by favoring taxa that are probably not the most efficient for some functions. Our results highlight that underneath the rustic appearance of the Cerrado vegetation there is a fragile soil microbial community.

Spatial distribution of an uranium-respiring betaproteobacterium at the Rifle, CO field research site

The Department of Energy’s Integrated Field-Scale Subsurface Research Challenge Site (IFRC) at Rifle, Colorado was created to address the gaps in knowledge on the mechanisms and rates of U(VI) bioreduction in alluvial sediments. Previous studies at the Rifle IFRC have linked microbial processes to uranium immobilization during acetate amendment. Several key bacteria believed to be involved in radionuclide containment have been described; however, most of the evidence implicating uranium reduction with specific microbiota has been indirect. Here, we report on the cultivation of a microorganism from the Rifle IFRC that reduces uranium and appears to utilize it as a terminal electron acceptor for respiration with acetate as electron donor. Furthermore, this bacterium constitutes a significant proportion of the subsurface sediment community prior to biostimulation based on TRFLP profiling of 16S rRNA genes. 16S rRNA gene sequence analysis indicates that the microorganism is a betaproteobacterium with a high similarity to Burkholderia fungorum. This is, to our knowledge, the first report of a betaproteobacterium capable of uranium respiration. Our results indicate that this microorganism occurs commonly in alluvial sediments located between 3-6 m below ground surface at Rifle and may play a role in the initial reduction of uranium at the site.

Homology modeling and protein engineering of alkane monooxygenase in Burkholderia thailandensis MSMB121: in silico insights

The degradation of hydrocarbons plays an important role in the eco-balancing of petroleum products, pesticides and other toxic products in the environment. The degradation of hydrocarbons by microbes such as Geobacillus thermodenitrificans, Burkhulderia, Gordonia sp. and Acinetobacter sp. has been studied intensively in the literature. The present study focused on the in silico protein engineering of alkane monooxygenase (ladA)-a protein involved in the alkane degradation pathway. We demonstrated the improvement in substrate binding energy with engineered ladA in Burkholderia thailandensis MSMB121. We identified an ortholog of ladA monooxygenase found in B. thailandensis MSMB121, and showed it to be an enzyme involved in an alkane degradation pathway studied extensively in Geobacillus thermodenitrificans. Homology modeling of the three-dimensional structure of ladA was performed with a crystal structure (protein databank ID: 3B9N) as a template in MODELLER 9v11, and further validated using PROCHECK, VERIFY-3D and WHATIF tools. Specific amino acids were substituted in the region corresponding to amino acids 305-370 of ladA protein, resulting in an enhancement of binding energy in different alkane chain molecules as compared to wild protein structures in the docking experiments. The substrate binding energy with the protein was calculated using Vina (Implemented in VEGAZZ). Molecular dynamics simulations were performed to study the dynamics of different alkane chain molecules inside the binding pockets of wild and mutated ladA. Here, we hypothesize an improvement in binding energies and accessibility of substrates towards engineered ladA enzyme, which could be further facilitated for wet laboratory-based experiments for validation of the alkane degradation pathway in this organism.