(221c) Engineering Magnetic Nanomaterial Production in Magnetotactic Bacteria Through Gene Regulation

Authors: 
Wilson, M. E., Carnegie Mellon University
González, L. M., Carnegie Mellon University
LeDuc, P. R., Carnegie Mellon University
Ruder, W. C., Carnegie Mellon University


Magnetotactic bacteria possess the unique ability to synthesize intracellular magnetic particles, known as magnetosomes, which form magnetic chains and yield cells responsive to the Earth’s ambient geomagnetic field.  While several genomic regions have been identified that encode magnetosome-related genes, little is known about how these genes regulate magnetosome production. Determining magnetic field-induced signaling modules is a critical step for being able to eventually utilize magnetotactic bacteria as biomaterials-producing machines via controlling the production of magnetic nanoparticles by simply turning on or off a magnetic switch.  Here, we explore the genetic response of Magnetospirillum magneticum strain AMB-1 to an applied electromagnetic field as a means to identify genes activated by magnetic stimulation.  We first established the magnetic stimulation parameters for eliciting transcriptional regulation of specific genes.  Optimal magnetic field strength and exposure time was determined via quantitative real time-PCR (qRT-PCR) utilizing in-house primer sets for genes related to the magnetosome island (MAI), magnetotactic islet, cytoskeleton and flagellar structures.  AMB-1 cultures were subjected to a uniform, high magnetic field (10G) within a solenoid for 1 hour, 3 hours or 8 hours.  After extracting total RNA and converting to cDNA, quantitative real time-PCR (qRT-PCR) was performed to measure relative transcription levels.  After 1 hour of magnetic stimulation, gene expression was drastically down-regulated; whereas, gene expression was up-regulated after 3 hours.  After 8 hours, gene expression was relatively unchanged, indicating that the AMB-1 cells may have adapted or equilibrated to the field.  These results suggest that magnetic stimulation leads to altered AMB-1 signaling related to MAI activation/deactivation, as well as cytoskeletal and flagellar regulatory events, and show the challenging nature of magnetically-induced responses that are dynamically changing.  We believe this research lays the groundwork for identifying endogenous gene network modules particularly active following application of concentrated magnetic field, which can be coupled with engineered gene circuits to create magnetically inducible synthetic devices.  Ultimately, we aim to design synthetic devices that allow organisms to serve as machines that detect specified magnetic field gradients and react by performing a specific function – e.g., directed cell movement for engineered tissue morphogenesis or upregulated production of magnetic nanoparticles that could be exploited in biomedical applications such as cancer ablation therapy.