Enhanced Biodegradation of Phenylurea Herbicides by Ochrobactrum anthrophi CD3 Assessment of Its Feasibility in Diuron-Contaminated Soils

Remediation of isoproturon-contaminated soil by Sphingobium sp. strain YBL2: Bioaugmentation, detoxification and community structure

The widely used phenylurea herbicide isoproturon (IPU) and its residues can inhibit the growth of subsequently planted crops. However, reports on bioremediation of IPU-contaminated soil are scarce. In this study, Sphingobium sp. strain YBL2-gfp (a derivative of the IPU-degrading Sphingobium sp. strain YBL2 isolated by our lab) was constructed to bioremediate IPU-contaminated soil. In pot experiments, strain YBL2-gfp colonized the roots of wheat and eliminated IPU residues in the soil within 21 d, effectively alleviating its toxicity and restoring wheat growth. IPU treatment reduced the richness and diversity of soil bacteria, while inoculation YBL2-gfp mainly affected richness with less impact on diversity. The high concentrations of IPU and inoculation of YBL2-gfp alone reduced the soil microbial community connections, while bioaugmentation treatment enhanced the soil microbial community connections. Additionally, strain YBL2-gfp stimulated the metabolic capacity of the indigenous microbes, promoting the degradation of IPU and reducing the negative impact of high concentrations of IPU on microbial community. Taken together, this study offers relatively comprehensive insights into the practical application of bioaugmentation, demonstrating that strain YBL2 has the potential to remediate IPU-contaminated soils.

Biodegradation of isoproturon by Escherichia coli expressing a Pseudomonas putida catechol 1,2-dioxygenase gene

The phenylurea herbicides are persistent in soil and water, necessitating the creation of methods for removing them from the environment. This study aimed to examine the soil microbial diversity, searching for local bacterial isolates able to efficiently degrade the phenylurea herbicide isoproturon, 3-(4-isopropylphenyl)-1, 1-dimethylurea (IPU). The best isolates able to effectively degrade IPU were selected, characterized, and identified as Pseudomonas putida and Acinetobacter johnsonii. The catechol 1, 2-dioxygenase enzyme's catA gene was amplified, cloned, and expressed in E. coli M15. The Expressed E. coli showed high degradation efficiency (44.80%) as analyzed by HPLC after 15 days of inoculation in comparison to P. putida (21.60%). The expression of the catA gene in P. putida and expressed E. coli was measured using quantitative polymerase chain reaction (qPCR). The results displayed a significant increase in the mRNA levels of the catA gene by increasing the incubation time with IPU. Hydrophilic interaction chromatography (HILIC) mass spectrometry analysis revealed that three intermediate metabolites, 1-(4-isopropylphenyl)-3-methylurea (MDIPU), 4-Isopropylaniline (4-IA) and 1-(4-isopropylphenyl) urea (DDIPU) were generated by both P. putida and expressed E. coli. In addition, IPU-induced catA activity was detected in both P. putida and expressed E. coli. The supernatant of both P. putida and expressed E. coli had a significant influence on weed growth. The study clearly exhibited that P. putida and expressed E. coli were capable of metabolizing IPU influentially and thus could be utilized for bioremediation and biodegradation technology development.

N-acetylation of toxic aromatic amines by fungi: Strain screening, cytotoxicity and genotoxicity evaluation, and application in bioremediation of 3,4-dichloroaniline

Aromatic amines (AA) are one of the most commonly used classes of compounds in industry and the most common pollutants found in both soil and water. 3,4-Dichloaniline (3,4-DCA) is a persistent residue of the phenylurea herbicide in the environment. In this study, we used a colorimetric method as a new approach to screen 12 filamentous fungal strains of the genera Aspergillus, Chaetomium, Cladosporium, and Mucor to assess their capacity to perform AA N-acetylation since it is considered a potential tool in environmental bioremediation. Subsequently, the selected strains were biotransformed with different AA substrates to evaluate the product yield. The strains Aspergillus niveus 43, Aspergillus terreus 31, and Cladosporium cladosporioides showed higher efficiencies in the biotransformation of 3,4-DCA at 500 µM into its N-acetylated product. These fungal strains also showed great potential to reduce the phytotoxicity of 3,4-DCA in experiments using Lactuca sativa seeds. Furthermore, N-acetylation was shown to be effective in reducing the cytotoxic and genotoxic effects of 3,4-DCA and other AA in the immortalized human keratinocyte (HaCaT) cell line. The isolated products after biotransformation showed that fungi of the genera Aspergillus and Cladosporium appeared to have N-acetylation as the first and main AA detoxification mechanism. Finally, A. terreus 31 showed the highest 3,4-DCA bioremediation potential, and future research can be carried out on the application of this strain to form microbial consortia with great potential for the elimination of toxic AA from the environment.

Bioremediation of a trifluralin contaminated soil using bioaugmentation with novel isolated bacterial strains and cyclodextrin

Trifluralin (TFL) is a highly persistent with a strong adsorption capacity on soil particles herbicide. This study was to isolate microbial consortia and bacterial strains from a soil with a historical application of pesticides to evaluate their potential to degrade TFL in soil. Different bioremediation techniques were considered for increasing the effectiveness of TFL degradation in soil. These techniques consisted of: i) biostimulation, using a nutrients solution (NS); ii) bioaugmentation, using a natural microbial consortium (NMC), seven individual bacterial strains isolated from NMC, and an artificial bacterial consortium formed by the seven TFL-degrading bacterial strains (ABC); iii) bioavailability enhancement, using a biodegradable compound, a randomly methylated cyclodextrin, RAMEB. Biostimulation using NS leads up to 34 % of soil TFL biodegraded after 100 d. When the contaminated soil was inoculated with NMC or ABC consortia, TFL loss increased up to 62 % and 74 %, respectively, with DT₅₀ values (required time for the pollutant concentration to decline to half of its initial value) of 5.9 and 11 d. In the case of soil inoculation with the isolated individual bacterial strains, the extent of TFL biodegradation ranged widely from 2.3 % to 55 %. The most efficient bacterial strain was Arthrobacter aurescens CTFL7 which had not been previously described in the literature as a TFL-degrading bacterium. Bioaugmentation with CTFL7 bacterium was also tested in the presence of RAMEB, provoking a drastic increase in herbicide biodegradation up to 88 %, achieving a DT₅₀ of only 19 d. Cyclodextrins had never been tested before for enhancement of TFL biodegradation. An ecotoxicity assay was performed to confirm that the proposed bioremediation techniques were also capable to reduce toxicity. A Microtox® test showed that after application A. aurescens CTF7 and A. aurescens CTF7 + RAMEB, the TFL-contaminated soil, which initially presented acute toxicity, became non-toxic at the end of the biodegradation experiments.