TL;DR
Results support the hypothesis that SNBT005 actively facilitates metal recovery and reveal some localized pitting and surface degradation of the PCB matrix as the result of microbial activity.
Heavy metal contamination arising from municipal, industrial, and biomedical waste disposal has emerged as a major environmental concern, contributing not only to ecosystem degradation but also to the co-selection and dissemination of antimicrobial resistance among environmental microorganisms. The present study aimed to isolate, characterize, and molecularly identify an antibiotic- and heavy metal-resistant (AHMR) bacterium from contaminated solid waste disposal sites in West Bengal, India, and to evaluate its potential for bioremediation of heavy metal-polluted environments. Soil samples collected from hospital, industrial, and municipal waste disposal sites were screened on nutrient agar supplemented with nickel (Ni), lead (Pb), and cadmium (Cd) (50 µg mL⁻¹), resulting in the recovery of seven morphologically distinct bacterial isolates. Antibiotic susceptibility profiling using the Kirby–Bauer disc diffusion method identified isolate S23 as the most resistant strain, exhibiting a multidrug resistance (MDR) index of 0.8 with resistance to gentamicin, tetracycline, penicillin, and amphotericin B. Heavy metal tolerance assays demonstrated a minimum inhibitory concentration (MIC) of approximately 100 µg mL⁻¹ for all three metals, with nickel producing the strongest inhibitory effect on bacterial growth. Physiological and biochemical characterization revealed that isolate S23 was a mesophilic, halotolerant, catalase-positive bacterium capable of utilizing multiple carbohydrates, including glucose and sucrose. Growth kinetics further demonstrated its ability to maintain sustained proliferation under heavy metal stress, indicating a high degree of environmental adaptability. Molecular identification based on 16S rRNA gene sequencing confirmed the isolate as Aeromonas hydrophila. The concurrent occurrence of multidrug antibiotic resistance and heavy metal tolerance supports the hypothesis of co-selection of resistance determinants in contaminated environments. Furthermore, the remarkable metal tolerance exhibited by A. hydrophila suggests its potential application in the bioremediation of heavy metal-contaminated soils and wastewater through mechanisms such as biosorption, bioaccumulation, and biotransformation. Overall, this study highlights the ecological significance of environmental A. hydrophila as a resilient microorganism with promising applications in sustainable remediation strategies while emphasizing the environmental role of polluted habitats as reservoirs for multidrug-resistant bacteria
Triclosan (TCS), a widely used pharmaceutical and personal care product (PPCP), has emerged as a significant environmental contaminant due to its widespread occurrence and associated ecological risks. Conventional wastewater treatment plant (WWTP) processes are often ineffective in completely removing TCS, emphasizing the need for more efficient and cost-effective treatment approaches. In the present study, bacterial isolates obtained from wastewater were evaluated for their ability to remove TCS at a concentration of 2 mg L-1 using free cells, microbial consortia, and immobilized systems. Three bacterial strains, namely Bacillus pumilus, Bacillus licheniformis, and Pseudomonas stutzeri, along with a consortium consisting of B. pumilus and B. licheniformis, were investigated for their TCS removal efficiency. Among the tested isolates, B. pumilus exhibited rapid removal of TCS, achieving approximately 90 % removal within 3 h. The microbial consortia showed enhanced performance compared to individual strains, reducing TCS concentrations to below the analytical detection limit. Furthermore, immobilized bacterial systems significantly improved the removal efficiency, indicating greater stability and sustained metabolic activity compared to free cells. Overall, the findings suggest that wastewater derived bacteria, particularly when employed as consortia and immobilized systems, represent a promising approach for the treatment of TCS contaminated wastewater.
To address heavy metal contamination in soils of the northern Shaanxi coal mining area, this study directionally screened and isolated a functional bacterial strain, Bacillus sp. NM-1, tolerant to Mn2+, Fe3+, and Cr6+, from polluted soil collected in the Shenmu mining region, Shaanxi Province, China. The isolate was identified as Bacillus sp. based on 16S rRNA gene sequencing analysis. A subsequent pot experiment was conducted to systematically evaluate the remediation efficacy of the selected strain in manganese-contaminated soil. Among the six metal-tolerant strains obtained, strain NM-1 exhibited the highest removal efficiency and the broadest concentration adaptability for Mn2+, Fe3+, and Cr6+, achieving over 99.5% removal of Mn2+ at an initial concentration of 100 mg/L. Subcellular distribution analyses of intracellular and extracellular ions, together with inactivated cell controls, revealed that extracellular adsorption constituted the primary mechanism underlying heavy metal removal. In the pot experiment, manganese ion (Mn2+) was used as the model contaminant. The results demonstrated that inoculation with NM-1 significantly alleviated manganese-induced growth inhibition in maize plants, as evidenced by increased plant height, biomass, and photosynthetic pigment content. Furthermore, NM-1 inoculation reduced malondialdehyde (MDA) accumulation while enhancing peroxidase (POD) activity and proline content, thereby improving the plant’s antioxidant capacity and osmotic regulation. Overall, this study provides a multifunctional metal-tolerant bacterial strain that represents a valuable microbial resource and offers theoretical support for microbe–plant combined remediation strategies in heavy metal-contaminated soils of the northern Shaanxi mining region.
