Assessment of homogeneous electro-Fenton process coupled with microbial fuel cell utilizing Serratia sp. AC-11 for glyphosate degradation in aqueous phase.

Glyphosate (GLY), a globally-used organophosphate herbicide, is frequently detected in various environmental matrices, including water, prompting significant attention due to its persistence and potential ecological impacts. In light of this environmental concern, innovative remediation strategies are warranted. This study utilized Serratia sp. AC-11 isolated from a tropical peatland as a biocatalyst in a microbial fuel cell (MFC) coupled with a homogeneous electron-Fenton (EF) process to degrade glyphosate in aqueous medium. After coupling the processes with a resistance of 100 Ω, an output voltage value of 0.64 V was obtained and maintained stable throughout the experiment. A bacterial biofilm of Serratia sp. AC-11 was formed on the carbon felt electrode, confirmed by attenuated total reflectance-Fourier transformed infrared (ATR-FTIR) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). In the anodic chamber, the GLY biodegradation rate was 100% after 48 h of experimentation, with aminomethylphosphonic acid (AMPA) remaining in the solution. In the cathodic chamber, the GLY degradation rate for the EF process was 69.5% after 48 h experimentation, with almost all of the AMPA degraded by the in situ generated hydroxyl radicals. In conclusion, the results demonstrated that Serratia sp. AC-11 not only catalyzed the biodegradation of glyphosate but also facilitated the generation of electrons for subsequent transfer to initiate the EF reaction to degrade glyphosate. This dual functionality emphasizes the unique capabilities of Serratia sp. AC-11, it as an electrogenic microorganism with application in innovative bioelectrochemical processes, and highlighting its role in sustainable strategies for environmental remediation.

Potential use of two Serratia strains for cadmium remediation based on microbiologically induced carbonate precipitation and their cadmium resistance.

Cadmium (Cd) presence and bioavailability in soils is a serious concern for cocoa producers. Cocoa plants can bioaccumulate Cd that can reach humans through the food chain, thus posing a threat to human health, as Cd is a highly toxic metal. Currently, microbiologically induced carbonate precipitation (MICP) by the ureolytic path has been proposed as an effective technique for Cd remediation. In this work, the Cd remediation potential and Cd resistance of two ureolytic bacteria, Serratia sp. strains 4.1a and 5b, were evaluated. The growth of both Serratia strains was inhibited at 4 mM Cd(II) in the culture medium, which is far higher than the Cd content that can be found in the soils targeted for remediation. Regarding removal efficiency, for an initial concentration of 0.15 mM Cd(II) in liquid medium, the maximum removal percentages for Serratia sp. 4.1.a and 5b were 99.3% and 99.57%, respectively. Their precipitates produced during Cd removal were identified as calcite by X-ray diffraction. Energy dispersive X-ray spectroscopy analysis showed that a portion of Cd was immobilized in this matrix. Finally, the presence of a partial gene from the czc operon, involved in Cd resistance, was observed in Serratia sp. 5b. The expression of this gene was found to be unaffected by the presence of Cd(II), and upregulated in the presence of urea. This work is one of the few to report the use of bacterial strains of the Serratia genus for Cd remediation by MICP, and apparently the first one to report differential expression of a Cd resistance gene due to the presence of urea.

Isolation of urease-producing bacteria from cocoa farms soils in Santander, Colombia, for cadmium remediation.

Cadmium (Cd) is a toxic heavy metal that causes serious health problems and is present in agriculturally important soils in Colombia, such as the ones used for cocoa farming. Recently, the use of ureolytic bacteria by the Microbiologically Induced Carbonate Precipitation (MICP) activity has been proposed as an alternative to mitigate the availability of Cd in contaminated soils. In this study, 12 urease-positive bacteria able to grow in the presence of Cd(II) were isolated and identified. Three were selected based on urease activity, precipitates formation and growth, with two belonging to the genus Serratia (codes 4.1a and 5b) and one to Acinetobacter (code 6a). These isolates exhibited low urease activity levels (3.09, 1.34 and 0.31 µmol mL-1 h-1, respectively), but could raise the pH to values close to 9.0 and to produce carbonate precipitates. It was shown that the presence of Cd affects the growth of the selected isolates. However, urease activity was not negatively influenced. In addition, the three isolates were observed to efficiently remove Cd from solution. The two Serratia isolates presented maximum removals of 99.70% and 99.62%, with initial 0.05 mM Cd(II) in the culture medium (supplemented with urea and Ca(II)) at 30 °C and 144 h of incubation. For the Acinetobacter isolate, the maximum removal was 91.23% at the same conditions. Thus, this study evidences the potential use of these bacteria for bioremediation treatments in samples contaminated with Cd, and it is one of the few reports that shows the high cadmium removal capacity of bacteria from the genus Serratia. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03495-1.

Phosphate-solubilizing Pseudomonas sp., and Serratia sp., co-culture for Allium cepa L. growth promotion.

Different genus of bacteria has been reported with the capacity to solubilize phosphorus from phosphate rock (PR). Pseudomonas sp., (A18) and Serratia sp., (C7) isolated from soils at the "Departamento de Boyacá" Colombia, where Allium cepa is cultivated. Bacteria were cultured in MT11B media and evaluated as a bio-fertilizer for A. cepa germination and growth during two months at greenhouse scale. Pseudomonas sp., and Serratia sp., cultured at 30 °C, 48 h in SMRS1 agar modified with PR, (as an inorganic source of phosphorus), presented a phosphate solubilization index (SI) of 2.1 ± 0.2 and 2.0 ± 0.3 mm, respectively. During interaction assays no inhibition halos were observed, demonstrating there was no antagonism between them. In MT11B media growth curve (12 h) demonstrated that co-culture can grow in the presence of PR and glucose concentrations 7.5-fold, lower than in SMRS1 media and brewer's yeast hydrolysate; producing phosphatase enzymes with a volumetric activity of 1.3 ± 0.03 PU at 6 h of culture and 0.8 ± 0.04 PU at 12 h. Moreover, co-culture released soluble phosphorus at a rate of 58.1 ± 0.28 mg L-1 at 8 h and 88.1 ± 0.32 mg L-1 at 12 h. After five days of evaluation it was observed that germination percentage was greater than 90 % of total evaluated seeds, when placing them in contact with the co-culture in a concentration of 1 × 108 CFU mL-1. Furthermore, it was demonstrated that co-culture application (10 mL per experimental unit to complete 160 mL in two months) at 8.0 Log10 CFU mL-1 twice a week for two months increased A. cepa total dry weight (69 ± 13 mg) compared with total dry weight (38 ± 5.0 mg) obtained with the control with water.

Density and diversity of diazotrophic bacteria isolated from Amazonian soils using N-free semi-solid media

Non-symbiotic diazotrophic bacteria are amongst the most important functional groups of soil-dwelling microorganisms. These bacteria contribute to plant growth predominantly through biological N2 fixation. Here, we evaluated the density and diversity of non-symbiotic diazotrophic bacteria in soils taken from diverse land use systems (LUS) in Amazonia using nitrogen-free media. A total of 30 soil samples were collected from the following LUS: pristine forest, young secondary forest, old secondary forest, agroforestry, agriculture and pasture. Bacterial density was evaluated by the most probable number (MPN) method utilizing N-free semi-solid media with varied compositions (JNFb, NFb, LGI and Fam). Individual isolates were characterized by colony and cellular morphology as well as total protein profiles and nitrogenase activity. Isolate genotypes were determined by partial 16S rDNA sequences. No typical diazotrophic growth in the JNFb medium was observed. Bacterial densities in the NFb medium were higher in the agriculture and agroforestry soil samples. In LGI and Fam media, bacterial densities were highest in the pasture soil samples. Overall, 22 isolates with high phenotypic diversity were obtained. Eleven isolates exhibited nitrogenase activity. Sequences of 16S rDNA genes of 14 out of 19 isolates had similarities below 100 % with known nitrogen-fixing species. Isolates were identified as belonging to the Burkholderia, Enterobacter, Serratia, Klebsiella, and Bacillus genera. A higher number of isolates from pasture soil samples were isolated, with the majority of these belonging to the Burkholderia and Bacillus genera. Among the isolates, unknown sequences were obtained, possibly indicating new species. Taken together, these data demonstrate that Fam, NFb, and LGI semi-solid media allowed the growth of diazotrophic bacteria belonging to different phylogenetic lines.

Density and diversity of diazotrophic bacteria isolated from Amazonian soils using N-free semi-solid media

Non-symbiotic diazotrophic bacteria are amongst the most important functional groups of soil-dwelling microorganisms. These bacteria contribute to plant growth predominantly through biological N2 fixation. Here, we evaluated the density and diversity of non-symbiotic diazotrophic bacteria in soils taken from diverse land use systems (LUS) in Amazonia using nitrogen-free media. A total of 30 soil samples were collected from the following LUS: pristine forest, young secondary forest, old secondary forest, agroforestry, agriculture and pasture. Bacterial density was evaluated by the most probable number (MPN) method utilizing N-free semi-solid media with varied compositions (JNFb, NFb, LGI and Fam). Individual isolates were characterized by colony and cellular morphology as well as total protein profiles and nitrogenase activity. Isolate genotypes were determined by partial 16S rDNA sequences. No typical diazotrophic growth in the JNFb medium was observed. Bacterial densities in the NFb medium were higher in the agriculture and agroforestry soil samples. In LGI and Fam media, bacterial densities were highest in the pasture soil samples. Overall, 22 isolates with high phenotypic diversity were obtained. Eleven isolates exhibited nitrogenase activity. Sequences of 16S rDNA genes of 14 out of 19 isolates had similarities below 100 % with known nitrogen-fixing species. Isolates were identified as belonging to the Burkholderia, Enterobacter, Serratia, Klebsiella, and Bacillus genera. A higher number of isolates from pasture soil samples were isolated, with the majority of these belonging to the Burkholderia and Bacillus genera. Among the isolates, unknown sequences were obtained, possibly indicating new species. Taken together, these data demonstrate that Fam, NFb, and LGI semi-solid media allowed the growth of diazotrophic bacteria belonging to different phylogenetic lines.

First isolation of microorganisms from the gut diverticulum of Aedes aegypti (Diptera: Culicidae): new perspectives for an insect-bacteria association

We show for the first time that the ventral diverticulum of the mosquito gut (impermeable sugar storage organ) harbors microorganisms. The gut diverticulum from newly emerged and non-fed Aedes aegypti was dissected under aseptic conditions, homogenized and plated on BHI medium. Microbial isolates were identified by sequencing of 16S rDNA for bacteria and 28S rDNA for yeast. A direct DNA extraction from Ae. aegypti gut diverticulum was also performed. The bacterial isolates were: Bacillus sp., Bacillus subtilis and Serratia sp. The latter was the predominant bacteria found in our isolations. The yeast species identified was Pichia caribbica.