Bioremediation potential of a multidrug-resistant Bacillus paramycoides BCSS17 isolated from a contaminated aquatic ecosystem

Heavy metal pollution in aquatic environments demands effective and sustainable bioremediation solutions. This study explores the potential of Bacillus paramycoides BCSS17, a
bacterial isolate from the contaminated waters of Buckingham Canal, for heavy metal resistance and biosorption. A total of 25 morphologically distinct bacterial isolates (BCSS01–
BCSS25) were recovered, with BCSS17 exhibiting the highest Maximum Tolerable
Concentration (MTC) values for lead (Pb, 2100 ppm), chromium (Cr, 1900 ppm), zinc (Zn),
manganese (Mn, 1700 ppm each), and copper (Cu, 1300 ppm). Antibiotic susceptibility tests
revealed multidrug resistance, and PCR amplification confirmed the presence of resistance
genes pbrA (Pb) and zntA (Zn). The 16S rRNA gene was first sequenced and analyzed, revealing 100% identity with Bacillus paramycoides. Following identification, the sequence was
submitted to the NCBI GenBank database and assigned the accession number PP989439.
Growth profiling in metal-supplemented media revealed that Bacillus paramycoides exhibited
robust growth with Pb (1.643) and Cu (1.583) at 25 h, moderate growth with Zn (1.587) and
Mn (1.442), while Cr resulted in the lowest growth, with a peak OD of 1.383. Biosorption
studies showed that BCSS17 exhibited the highest uptake for Pb (5.024 ± 0.57 mg/g at
100 ppm) and significant Zn uptake (4.128 ± 0.52 mg/g at 200 ppm). Bioaccumulation analysis
revealed maximum accumulation of Zn (73.128 ± 0.62%) and Pb (69.435 ± 0.33%), even at
higher concentrations, highlighting its strong biosorption potential. Scanning electron
microscopy (SEM) analysis revealed morphological alterations in bacterial cells post-metal
exposure, indicating surface-level interactions with heavy metals, while Fourier-transform
infrared (FTIR) spectroscopy confirmed the involvement of functional groups such as
hydroxyl (-OH), carboxyl (-COOH), amide (–CONH2), and phosphate (–PO4
3-), indicating their
role in heavy metal binding. Molecular docking studies further supported these findings,
revealing that Metallo beta-lactamase exhibited the strongest binding affinity with Zn
(–9.6 kcal/mol), followed by Pb (–8.6 kcal/mol) and Mn (–8.3 kcal/mol), involving key interacting residues such as HIS61, HIS134, and ASP63. The novelty of this study lies in the discovery that BCSS17 exhibits exceptionally high MTC values, dual metal-resistance genes (pbrA
and zntA), and superior Pb and Zn biosorption capacities—levels significantly higher than
those reported for previously characterized Bacillus strains. These results underscore Bacillus
paramycoides BCSS17 as a highly promising candidate for the bioremediation of heavy
metal-contaminated aquatic ecosystems.