Metal tolerance and biosorption capacities of bacterial strains isolated from an urban watershed

Abstract

Rapid industrialization and urbanization have led to widespread metal contamination in aquatic ecosystems. This study explores the metal tolerance and biosorption characteristics of four bacterial strains (Serratia sp. L2, Raoultella sp. L30, Klebsiella sp. R3, and Klebsiella sp. R19) isolated from Saint Clair River sediments. These strains effectively removed various metal cations (As3+, Pb2+, Cu2+, Mn2+, Zn2+, Cd2+, Cr6+, and Ni2+) in single and multi-metal solutions. Minimum inhibitory concentration (MIC) assays revealed strain-specific variations in metal tolerance, with L2 and L30 exhibiting higher tolerance. Surprisingly, R3 and R19, despite lower tolerance, demonstrated superior metal removal efficiency, challenging the notion that tolerance dictates removal efficacy. In single-metal solutions, R3 and R19 excelled at extracting various metal ions, while competitive binding in multi-metal solutions hindered removal. However, R3 and R19 retained higher removal efficiencies, possibly due to enhanced flocculation activities facilitating metal-ion contact. Comprehensive Fourier-transform infrared (FTIR) analysis highlighted the strains’ metal-binding capabilities, with novel peaks emerging after metal exposure, indicative of extracellular polymeric substance (EPS) production. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed metal accumulation on bacterial surfaces and within cytoplasmic regions and revealed morphological changes and metal adsorption patterns, emphasizing the strains’ ability to adapt to metal stress. Scanning transmission microscopy (STEM) and EDX analysis uncovered metal accumulation within bacterial cells, underscoring the complexity of microbial-metal interactions. This study also confirms that the simultaneous presence of an aqueous solution may cause a mutual inhibition in the adsorption of each metal to the EPS resulting in reduced metal uptake, which emphasizes the need to select specific bacterial strains for a given metal-containing effluent. The differences in metal distribution patterns between Klebsiella sp. R19 and Raoultella sp. L30 suggest species-specific metal accumulation strategies driven by environmental conditions and metal availability. The heavy metal-removing capabilities and the ability to grow over a wide range of metal concentrations of the strains used in this study may offer an advantage to employ these organisms for metal remediation in bioreactors or in situ.

Applications of Fourier Transform-Infrared spectroscopy in microbial cell biology and environmental microbiology: advances, challenges, and future perspectives

“…Microbial biosorption has gained prominence as an environmentally friendly method for extracting heavy metals from water (Bowman et al, 2018;Tiquia-Arashiro, 2018, Pagnucco et al, 2023. This process involves a variety of interactions between microbial cell surfaces and metal ions, including physical adsorption, ion exchange, complexation, and surface precipitation (Tiquia-Arashiro, 2018;Tiquia-Arashiro and Pant, 2019;Pagnucco et al, 2023). FT-IR spectroscopy allows researchers to investigate the molecular-level alterations on microbial cell surfaces during metal binding.…”

“…These modifications provide valuable information about the specific functional groups responsible for metal absorption and the ensuing chemical reactions on the microbial cell surface. Comprehensive analysis of biosorption of metal ions using FT-IR have been studied in bacteria (Pardo et al, 2003;Oh et al, 2009;Gutiérrez-Corona et al, 2016;Dhanwal et al, 2018;Saranya et al, 2018;Pagnucco et al, 2023), algae (Michalak et al, 2013;Gu and Lan, 2021) and fungi (George et al, 2012;Gutiérrez-Corona et al, 2016;Sundararaju et al, 2022;Table 9).…”

“…This has contributed to the management of water quality, assessment of ecosystem health, and the detection of microbial pollution. In the context of metal-pollutant bioremediation, FTIR has enabled the comprehensive analysis of how microorganisms interact with metal contaminants (Pagnucco et al, 2023). This has helped in understanding the mechanisms involved in metal sequestration, transformation, and detoxification.…”

New strontium-based coatings show activity against pathogenic bacteria in spine infection

“…Some bacterial cells on Sr-TCP coating also showed cracks and alterations in their rod-shape ( E. coli ) and spherical ( S. aureus ) morphology. Changes in the cell morphology may be either a consequence of the disruption and loss of functionality of the bacterial cells or an attempt of the bacterial cells to tolerate the toxicity of the metal present on the surface by modifying its cellular structure ( Mathivanan et al, 2021 ; Pagnucco et al, 2023 ). Based on what is known for other toxic metals, strontium might also inhibit the expression of genes involved in bacterial cell wall formation and production of septal peptidoglycan during cell division with possible effects on cellular morphology ( Ahmed et al, 2020 ).…”

Bioremoval of Lead by Bacillus amyloliquefaciens Mpa 1034 Isolated from Wastewater Textile Factories at El-Mahala El-Kobra City, Egypt

“…FTIR spectroscopy is a powerful tool for monitoring and revealing microorganism composition and responses to the environment. So, it was performed to confirm the interactions between metal ions and functional groups on the surface of the microbial cells in comparison to untreated ones (Dhanwal et al,2018;Rizvi and Saghir-Khan 2019;Pagnucco et al,2023 and. Where, Dhanwal et al,(2018) identified the surface chemical functional groups of the metal tolerant strain, Bacillus cereus FIT10, by FTIR spectroscopy as hydroxyl, carboxyl, amine, and halide, which might be involved in the biosorption of heavy metals, lead, chromium, copper, and nickel.…”