<i>Borrelia burgdorferi</i> radiosensitivity and Mn antioxidant content: antigenic preservation and pathobiology

The bacterium responsible for Lyme disease, <i>Borrelia burgdorferi</i>, accumulates high levels of manganese without iron and possesses a polyploid genome, characteristics suggesting potential extreme resistance to radiation. Contrary to expectations, we report that wild-type <i>B. burgdorferi</i> B31 cells are radiosensitive, with a gamma-radiation survival limit for 10⁶ wild-type cells of <1 kGy. Thus, we explored <i>B. burgdorferi</i> radiosensitivity through electron paramagnetic resonance (EPR) spectroscopy by quantitating the fraction of Mn²⁺ present as antioxidant Mn²⁺ metabolite complexes (H-Mn). The spirochetes displayed relatively low levels of H-Mn, in stark contrast to the extremely radiation-resistant <i>Deinococcus radiodurans</i>. The H-Mn content as revealed by EPR spectroscopy is sufficiently sensitive to detect small changes in radiosensitivity among <i>B. burgdorferi</i> strains. However, <i>B. burgdorferi</i> cells are significantly more sensitive than predicted by EPR, implicating their linear genome architecture as an additional explanation for radiosensitivity. We then explored the influence of the Mn²⁺-decapeptide-phosphate antioxidant complex MDP, known to shield proteins during irradiation, and showed that treatment with MDP preserves <i>B. burgdorferi's</i> epitopes at 5 kGy irradiation, which crucially prevents cell proliferation. This finding defines some of the pivotal mechanisms that <i>B. burgdorferi</i> evolved to survive oxidative conditions experienced with tick and mammal immune responses. These observations also provide an opportunity for innovative vaccine development strategies employing ionizing radiation to disrupt the <i>B. burgdorferi</i> genome, while maintaining antigenic potency. These fresh insights extend our understanding of the unique biology of <i>B. burgdorferi</i> and open new avenues for considering novel whole-cell Lyme disease vaccines using MDP and irradiation-based inactivation.IMPORTANCEThe study highlights that electron paramagnetic resonance (EPR) spectroscopy is sufficiently sensitive to detect small differences in radiation resistance among <i>Borrelia burgdorferi</i> strains based on their population of Mn²⁺-metabolite complexes (H-Mn). <i>B. burgdorferi</i> appears to have evolved a system not to protect from irradiation, but presumably to protect from oxidative stress when cyclically transmitted from tick to mammalian host and back. These data also suggest a path forward in the development of novel vaccines against spirochete infections, including Lyme disease, through preparation involving the synthetic Mn²⁺-decapeptide-phosphate antioxidant complex MDP to provide <i>B. burgdorferi</i> epitope protection during sterilizing gamma-irradiation that eliminates growth. Given the current lack of effective whole-cell vaccines for Lyme disease, this research identifies a potential strategy for developing alternative radiation-inactivated, yet highly effective vaccines.