Pioneering research: Harnessing magnetotactic bacteria to purify uranium-contaminated water

Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have achieved a significant breakthrough in water purification by utilizing magnetotactic bacteria. These unique bacteria possess the ability to respond to magnetic fields and can accumulate heavy metals, such as uranium, within their cell walls. This novel discovery also provides valuable insights into the interaction between uranium and bioligands.

Dr. Evelyn Krawczyk-Bärsch from HZDR’s Institute of Resource Ecology explains, “Our experiments focus on the potential industrial applications of microbiological water remediation, particularly in cases where water is contaminated with heavy metals commonly found in abandoned uranium mines.” Her colleague, Dr. Johannes Raff, further adds, “For this project, we sought the assistance of a remarkable group of organisms known as magnetotactic bacteria. Due to their unique structure, they are exceptionally well-suited for such tasks.”

Magnetotactic bacteria possess a distinguishing feature that sets them apart from other bacteria—namely, they produce nanoscopic magnetic crystals within their cells. These crystals are arranged in a linear fashion, resembling a string of beads, and are so impeccably formed that replicating them synthetically remains beyond human capabilities. Each individual crystal is encased within a protective membrane, collectively forming a structure called the magnetosome. This magnetosome enables the bacteria to align themselves with the Earth’s magnetic field and navigate their surroundings. It also facilitates straightforward separation processes.

Magnetotactic bacteria are ubiquitous in various aquatic environments, ranging from freshwater to saltwater, including environments with limited nutrients. Microbiologist Dr. Christopher Lefèvre has even discovered these bacteria in the hot springs of Nevada. The researchers at Rossendorf acquired their strain of bacteria from Dr. Lefèvre and his colleague Dr. Damien Faivre from the French Alternative Energies and Atomic Energy Commission (CEA). They also received expert guidance on the preservation of these bacteria, as cultivating them requires specialized knowledge despite their relative abundance.

Stable heavy metal collectors in a hostile environment

Magnetotactic bacteria exhibit remarkable resilience to high concentrations of uranium, even at neutral pH levels. These bacteria have the exceptional ability to bind uranium predominantly within their cell walls, making them highly suitable for tackling water conditions associated with mining. Interestingly, uranium does not permeate the interior of the cell or interact with the magnetosome, the distinctive magnetic crystal structure found within the bacteria.

While it was already known that different bacterial types could bind heavy metals in their cell walls, magnetotactic bacteria present a unique case. Their cell walls consist of a peptidoglycan layer, a macromolecule comprising sugars and amino acids, which is typically around four nanometers thick and is a primary component of many bacterial cell walls.

The cell walls of magnetotactic bacteria are enveloped by an outer membrane composed of sugars and lipid-like components, which serve as potential binding sites for uranium.

Dr. Krawczyk-Bärsch explains, “Our findings indicate that peptidoglycan plays a significant role in uranium absorption in magnetotactic bacteria. This discovery is both new and unexpected for this bacterial group.” The research team successfully identified three distinct species of uranium-bound peptidoglycan and verified their findings using reference samples. This breakthrough was made possible through the combination of microscopy and various spectroscopic techniques, a rare integration of expertise found at very few research institutions worldwide.

Dr. Raff emphasizes the advantages of collaborating with the Institute of Ion Beam Physics and Materials Research at HZDR, stating, “Our partnership allowed us to utilize the electron microscope, among other resources. The close proximity of our institutes and the expertise of our colleagues provide significant benefits for our research endeavors.”

Significance for purifying contaminated water

The magnetic properties of magnetotactic bacteria offer a convenient means of separating them from water using magnets. Dr. Krawczyk-Bärsch envisions the potential for large-scale applications, such as conducting the treatment directly in surface water or establishing pilot treatment plants to pump water from underground mines.

Utilizing magnetotactic bacteria presents an effective and cost-efficient alternative to conventional chemical treatments. These bacteria have low maintenance requirements compared to other biomass-based solutions, which often incur higher costs due to increased nutrient and energy demands.

Another intriguing aspect that has captured the researchers’ attention is the ability of magnetotactic bacteria proteins to stabilize divalent and trivalent iron, facilitating the synthesis of magnetite within the magnetosomes. Dr. Raff elaborates on their curiosity, stating, “We are particularly interested in understanding how these microorganisms interact with radionuclides in different oxidation states, especially in relation to plutonium.” Unlike uranium, plutonium’s chemical similarity to iron may allow it to employ alternative pathways to enter the cell. Exploring these dynamics has implications for understanding plutonium’s migration behavior in nature and investigating the potential of utilizing magnetotactic bacteria to remove plutonium from wastewater. Consequently, this research is relevant to repository studies, where the findings can contribute to safety assessments.

The research findings have been published in the Journal of Hazardous Materials.

Source: Helmholtz Association of German Research Centres

Leave a Comment