Search

IntroductionSoil bacteria offer a promising approach to bioremediate pesticide contamination in agricultural ecosystems. This study investigated the potential of bacteria isolated from rice paddy soil for bioremediating fipronil and thiobencarb, common agricultural pesticides.MethodsBacterial isolates capable of degrading fipronil and thiobencarb were enriched in a mineral salt medium. A response surface methodology with a Box-Behnken design was utilized to optimize pesticide degradation with the isolated bacteria. Bioaugmentation tests were performed in paddy soils with varying conditions.Results and discussionSix strains, including single isolates and their mixture, efficiently degraded these pesticides at high concentrations (up to 800 µg/mL). Enterobacter sp., Brucella sp. (alone and combined), and a mixture of Stenotrophomonas sp., Bordetella sp., and Citrobacter sp. effectively degraded fipronil and thiobencarb, respectively. Notably, a single Pseudomonas sp. strain degraded a mixture of both pesticides. Optimal degradation conditions were identified as a slightly acidic pH (6-7), moderate pesticide concentrations (20-50 µg/mL), and a specific inoculum size. Bioaugmentation assays in real-world paddy soils (sterile/non-sterile, varying moisture) demonstrated that these bacteria significantly increased degradation rates (up to 14.15-fold for fipronil and 5.13-fold for thiobencarb). The study identifies these novel bacterial strains as promising tools for bioremediation and bioaugmentation strategies to tackle fipronil and thiobencarb contamination in paddy ecosystems.

IntroductionFipronil (FIP) and thiobencarb (THIO) represent widely utilized pesticides in paddy fields, presenting environmental challenges that necessitate effective remediation approaches. Despite the recognized need, exploring bacterial consortia efficiently degrading FIP and THIO remains limited.MethodsThis study isolated three unique bacterial consortia—FD, TD, and MD—demonstrating the capability to degrade FIP, THIO, and an FIP + THIO mixture within a 10-day timeframe. Furthermore, the bioaugmentation abilities of the selected consortia were evaluated in paddy soils under various conditions.ResultsSequencing results shed light on the consortia’s composition, revealing a diverse bacterial population prominently featuring Azospirillum, Ochrobactrum, Sphingobium, and Sphingomonas genera. All consortia efficiently degraded pesticides at 800 µg/mL concentrations, primarily through oxidative and hydrolytic processes. This metabolic activity yields more hydrophilic metabolites, including 4-(Trifluoromethyl)-phenol and 1,4-Benzenediol, 2-methyl-, for FIP, and carbamothioic acid, diethyl-, S-ethyl ester, and Benzenecarbothioic acid, S-methyl ester for THIO. Soil bioaugmentation tests highlight the consortia’s effectiveness, showcasing accelerated degradation of FIP and THIO—individually or in a mixture—by 1.3 to 13-fold. These assessments encompass diverse soil moisture levels (20 and 100% v/v), pesticide concentrations (15 and 150 µg/g), and sterile conditions (sterile and non-sterile soils).DiscussionThis study offers an understanding of bacterial communities adept at degrading FIP and THIO, introducing FD, TD, and MD consortia as promising contenders for bioremediation endeavors.

This research aimed to optimize a lipopeptide biosurfactant produced from Bacillus sp. SHA302 due to its high efficiency of heavy metal release in soil. The results demonstrated that the metal release capacity of the lipopeptide biosurfactant alone increased with increasing the biosurfactant concentration. Among treatments with different biosurfactant concentrations plus acid, the highest metal release rates of 53.8% ± 1.4 and 39.3% ± 1.7 for Zn and Pb, respectively, were observed in the critical micelle concentration (CMC) + HCl treatment. The results of a factorial experiment designed for optimizing biosurfactant production showed that among five inexpensive carbon sources and six mineral nitrogen sources, sugar beet molasses (1%) and ammonium chloride (0.1%) were the most efficient sources in lowering the surface tension (ST) of the culture media to 32.2 ± 0.76 mN/m. The second step of the experiment was a Plackett–Burman design with 11 factors and showed that the four factors of pH, ammonium chloride, magnesium sulfate, and molasses significantly affected (P < 0.05) the changes in ST and biosurfactant production. The third step of the experiment was done using the response surface methodology (RSM) with a central composite design. The results showed that a pH of 7.3, 1.5 g/l of ammonium chloride, 0.3 g/l of magnesium sulfate, and 10% of sugar beet molasses yielded values of 29.2 ± 0.71 mN/m and 5.74 ± 0.52 g/l for the two variables of ST and biosurfactant production, respectively, which reached their most optimal levels.

Hydrocarbon contamination emerging from the crude oil industrial-related activities has led to severe environmental issues. Prolonged contamination with the constant infiltration of crude oil into the soil is a severe problem in remediating contaminated soils. Hence, the current study focuses on comparing various bioremediation strategies, thereby isolating native bacteria competent to reduce TPH in both liquid and microcosm environments in an old-aged petroleum hydrocarbon contaminated soil. Assays in the modified 6SW-Vit medium after 7 days of incubation revealed that Bacillus altitudinis strain HRG-1 was highly hydrophobic and had a suitable ability to decrease surface tension (40.98%) and TPH (73.3%). The results of biodegradation in the microcosm proved that among the designated treatments, including bio-stimulated microcosm (SM), bacterialized microcosm (BM), a combined bio-stimulated microcosm and bacterialized microcosm (SB), and natural attenuation (NA), the SB treatment was the most effective in mitigating TPH (38.2%). However, the SM treatment indicated the lowest TPH biodegradation (18%). Pearson correlation coefficient among microcosm biological indicators under investigation revealed that soil basal respiration had the highest correlation with the amount of residual TPH (r = −0.73915, P < 0.0001), followed by the microbial population (r = −0.65218, P < 0.0001), catalase activity (r = 0.48323, P = 0.0028), polyphenol oxidase activity (r = −0.43842, P = 0.0075), and dehydrogenase activity (r = −0.34990, P = 0.0364), respectively. Nevertheless, considering the capability of strain HRG-1 and the higher efficiency of the combined technique, their use is recommended to diminish the concentration of petroleum hydrocarbons in hot and dry contaminated areas.