Magnetotactic Bacteria Nanoparticles Functionalized for Biomedical Control

Published in the Annals of Microbiology in April 2026, the short communication details the isolation of Klebsiella species AK01 and Priestia species AK02, along with the purification and analysis of their magnetosomes. The study highlights the ability to control bacterial movement using external magnetic fields within a microfluidic system, suggesting a pathway toward microrobotic applications in biotechnology.

The team collected soil samples from diverse environments in the Southern Karnataka region, including lake beds, rhizosphere soils, and areas around mineral-rich mountains. Approximately 100 grams of soil were taken from a depth of 2 to 4 centimeters at each site. These samples were serially diluted in sterile saline and inoculated into fluid thioglycolate broth, a medium previously standardized for the isolation of magnetotactic bacteria from aerobic forest soils. The enrichment process involved incubation for 168 hours at 30 degrees Celsius in the presence of applied neodymium magnets, a technique designed to select for bacteria that exhibit magnetic orientation.

Out of nine soil samples tested, all showed enriched presence of magnetotactic bacteria, but only two maintained consistent activity during sub-culturing. Sample 4, taken from the backwaters of the KRS dam, and Sample 8, from Coorg, confirmed the movement of colonies toward the applied magnetic field. These isolates were designated AK01 and AK02, respectively. Molecular characterization using 16S rDNA sequencing identified AK01 as a Klebsiella species and AK02 as a Priestia species, with sequences submitted to the NCBI GenBank under accession numbers PP886460.1 and PP869085.1. Phylogenetic analysis using the Maximum Likelihood method and Tamura-Nei model confirmed the evolutionary relationships of these isolates relative to an Escherichia coli outgroup.

The magnetosomes, which are lipid-bound magnetic crystals within the bacteria, were isolated and purified from the two strains. The purification process involved growing the bacteria in fluid thioglycolate broth, pelleting the cells, and resuspending them in 2 M potassium hydroxide. The solution was incubated at 80 degrees Celsius for one hour, and the magnetically active materials were collected using external magnets. The total yield of purified magnetic nanoparticles was 859 milligrams for isolate AK01 and 619 milligrams for isolate AK02, indicating a significant capacity for magnetic mineral sequestration in these soil-derived bacteria.

Characterization of the nanoparticles was performed using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. X-ray diffraction confirmed the crystalline nature of the nanoparticles, with characteristic peaks indicating magnetite crystals and a size range of approximately 50 nanometers. Scanning electron microscopy revealed an average nanoparticle size of 50 nanometers, while energy dispersive X-ray analysis detected the presence of iron at 0.58 percent in AK01 and 0.2 percent in AK02, alongside other monovalent cations and anions. Fourier transform infrared spectroscopy identified iron oxide-based signatures at specific wavenumbers, confirming the composition of the magnetosome nanoparticles.

To explore biomedical applications, the researchers functionalized the magnetic nanoparticles by immobilizing commercial fungal alpha-amylase. The enzyme was fixed onto 50 milligrams of nanoparticles using glutaraldehyde, a cross-linking agent, and incubated at 40 degrees Celsius for 30 minutes. The immobilization was confirmed by Fourier transform infrared spectroscopy, which showed amino stretches associated with bound primary amines and carbon-nitrogen bonds. This functionalization process is significant because it allows for the attachment of biomolecules to magnetic particles, potentially enabling their use in drug delivery, biofilm removal, or diagnostic assays where external magnetic control is required.

Enzymatic activity analysis demonstrated that the functionalized nanoparticles retained catalytic function. The magnetic nanoparticles alone showed no innate activity, but after functionalization, AK01 exhibited an activity of 1.07 micromoles per minute per milliliter, and AK02 showed 1.09 micromoles per minute per milliliter. This corresponded to 0.2675 and 0.2725 units of enzyme immobilized per milligram of nanoparticles, respectively. Statistical analysis indicated that the enzymatic activity was significantly higher than the magnetosome controls, with a p-value of less than 0.05, confirming the successful and stable immobilization of the enzyme on the magnetic surface.

The study also investigated the magnetic actuation of the bacteria within a microfluidic flow cell. A mould for the flow cell was constructed using a 3D printer with PLA resin, and the flow channels were set at 100 micrometers. The basic flow cell was constructed using 3 percent agarose and 3 percent soluble starch, which provided stable channel dimensions compared to lower concentrations that resulted in distorted channels. The flow cell was filled with a suspension of isolate AK01, and the movement of the bacteria was observed under a compound microscope at 100X magnification.

By placing magnets at different directions relative to the flow cell, the researchers demonstrated controlled accumulation of the magnetotactic bacteria at specific corners of the channels. This magnetic actuation suggests that the bacteria can be directed to specific sites of action, a key requirement for their potential use as microrobots in biomedical settings. The ability to control the movement of these bacteria using external magnetic fields, combined with the functionalization of their nanoparticles, expands the repertoire of microbial applications in biotechnology and biomedicine.

The isolation of aerobic magnetotactic bacteria remains a challenge due to the oxygen sensitivity of magnetite and the complex redox stabilization required for magnetosome formation in oxic-anoxic conditions. Previous studies have predominantly reported magnetotactic bacteria from aquatic or microaerophilic environments, making the isolation from dry lakebeds and agricultural soils in this study a notable extension. The use of fluid thioglycolate medium with resazurin to reduce oxygen levels facilitated the consistent isolation of these strains from aerobic samples, addressing a significant methodological hurdle in the field.

The findings indicate that the isolated Klebsiella and Priestia species possess the ability to sequester environmental metal ions to form functional cytoplasmic magnetic crystals. The characterization of their magnetosomes as magnetic nanoparticles with defined size and composition provides a foundation for further development in bioelectronic devices, biosensors, and targeted therapy. The functionalization with alpha-amylase serves as a proof of concept for attaching other biomolecules, potentially allowing for the creation of specialized magnetic tools for medical diagnostics and treatment.

The study concludes that the isolated magnetotactic bacteria and their magnetosome nanoparticles exhibit the ability to be functionalized and controlled using external actuators. This work enhances the understanding of microbial applications in bacteria that were previously not reported in such contexts, offering a new perspective on the use of magnetotactic bacteria in microrobotic vistas of biotechnology. The data supports the potential for these organisms to serve as versatile platforms for biomedical interventions where precise magnetic control is advantageous.

The research was published as a short communication in the Annals of Microbiology, Volume 76, article number 29, in April 2026. The authors positioned this work as an extension of previous methods for isolating magnetotactic bacteria from aerobic environments, specifically addressing the challenge of stabilizing oxygen-sensitive magnetite in prokaryotic cells.

Magnetotactic bacteria are described as a polyphyletic group capable of sequestering environmental metal ions to form functional cytoplasmic magnetic crystals. These crystals are enclosed within packets of lipids known as magnetosomes, which help the bacteria orient themselves relative to Earth’s magnetic fields based on the redox nature of their environment. While these organisms are widely distributed, they are predominantly reported from aquatic or microaerophilic habitats where chemical stratification favors magnetic mineral synthesis. The presence of a single-layer lipid membrane around the mineralized crystals helps the cell to exhibit localized magnetism in packets called magnetosomes.

The discussion highlights that conventional isolation techniques often involve magnetic response-based methods, cultivation in enrichment media, and microscopic scrutiny. However, the isolation of aerobic magnetotactic bacteria remains rare because the mechanism for redox stabilization of aerobic magnetosomes is complex. The authors note that the genus Priestia, from which isolate AK02 was identified, has been reclassified from the genus Bacillus and has been reported multiple times for iron sequestration and biomagnetism. Similarly, the genus Klebsiella, identified for isolate AK01, has been reported for its ability to mineralize iron into intracellular particles, providing a biological context for the magnetic properties observed in these soil isolates.

The potential applications of these functionalized nanoparticles extend beyond simple enzymatic assays. The authors suggest that the biocompatibility of magnetosomes enhances their utility in targeted drug delivery, diagnostic tools, and as contrast agents in magnetic resonance imaging. The ability to immobilize biomolecules onto magnetic nanoparticles allows for their use in drug delivery and biofilm removal, with the added advantage of external magnetic control. This control mechanism is crucial for directing the nanoparticles to specific sites of action, a requirement for their effective use in biomedical settings.

The study emphasizes that the ability to use magnetotactic bacteria as microrobots in flow cells has been conceptualized previously, but the specific control mechanisms need to be studied individually for each isolated strain. The use of basic agarose-based flow cells helps in evaluating the magnetic actuation of these bacteria, driving them to the site of action when functionalized. This approach provides a rudimentary model for understanding how external actuators can influence microbial movement, which is a key step toward developing more complex micro-robotic applications in biotechnology and biomedicine.

Subject of Research: Isolation and functionalization of magnetotactic bacteria nanoparticles for biomedical applications

Article Title: Functionalization of magnetotactic bacterial isolates and their nanoparticles for potential applications in biomedicine

Article References: Narayan, A., Hegde, K., & Markande, A. R. (2026). Functionalization of magnetotactic bacterial isolates and their nanoparticles for potential applications in biomedicine. Annals of Microbiology, 76(1), Article 29. https://doi.org/10.1186/s13213-025-01798-7

Image Credits: AI Generated

DOI: 10.1186/s13213-025-01798-7

Keywords: magnetotactic bacteria, magnetic nanoparticles, biomedical applications, enzyme immobilization, microfluidics, Klebsiella, Priestia, magnetosomes, biotechnology, Southern Karnataka, Functionalization, magnetotactic