Image-based physical characterization of magnetotactic bacteria from an environmental sample.

Magnetotactic bacteria (MTB) are a diverse group of microorganisms that are able to biomineralize magnetic nanoparticles. Most MTB remain uncultured, making population-level characterization of samples from natural environments difficult. The article reports on the discovery of a new and diverse MTB-rich site in the Ogre River, Latvia, and presents an integrated approach that combines 16S rRNA gene sequencing, transmission electron microscopy, and two novel open-source, automated, image-based physical methods to characterize bacteria populations within environmental samples. A pipeline for cell velocimetry is introduced, which uses a static magnetic field and a method to classify cell populations based on their magnetic moment using a modified U-turn method, where cell behavior is studied in an alternating magnetic field. This study demonstrates that image-based analysis methods provide a powerful, fast, and robust tool set for the analysis of MTB populations in complex environmental samples. IMPORTANCE: Magnetotactic bacteria are microorganisms that can be controlled using a magnetic field. They have potential applications in medicine, robotics, and environmental engineering, yet most species remain uncultured and poorly characterized. In this study, we report the discovery of a new MTB-rich site in the Ogre River, Latvia, and introduce open-source image-based methods that enable rapid and automated analysis of MTB directly from environmental samples. This accessible toolkit expands the methods to study MTB ecology and diversity, offering a robust framework for future ecological and applied microbiology research.