Multifactorial Resistance ofBacillus subtilisSpores to High-Energy Proton Radiation: Role of Spore Structural Components and the Homologous Recombination and Non-Homologous End Joining DNA Repair Pathways

Abstract

The space environment contains high-energy charged particles (e.g., protons, neutrons, electrons, a-particles, heavy ions) emitted by the Sun and galactic sources or trapped in the radiation belts. Protons constitute the majority (87%) of high-energy charged particles. Spores of Bacillus species are one of the model systems used for astro-and radiobiological studies. In this study, spores of different Bacillus subtilis strains were used to study the effects of high energetic proton irradiation on spore survival. Spores of the wild-type B. subtilis strain [mutants deficient in the homologous recombination (HR) and non-homologous end joining (NHEJ) DNA repair pathways and mutants deficient in various spore structural components such as dipicolinic acid (DPA), a/b-type small, acidsoluble spore protein (SASP) formation, spore coats, pigmentation, or spore core water content] were irradiated as air-dried multilayers on spacecraft-qualified aluminum coupons with 218 MeV protons [with a linear energy transfer (LET) of 0.4 keV/lm] to various final doses up to 2500 Gy. Spores deficient in NHEJ-and HR-mediated DNA repair were significantly more sensitive to proton radiation than wild-type spores, indicating that both HR and NHEJ DNA repair pathways are needed for spore survival. Spores lacking DPA, a/b-type SASP, or with increased core water content were also significantly more sensitive to proton radiation, whereas the resistance of spores lacking pigmentation or spore coats was essentially identical to that of the wild-type spores. Our results indicate that a/b-type SASP, core water content, and DPA play an important role in spore resistance to high-energy proton irradiation, suggesting their essential function as radioprotectants of the spore interior.

Candidate Genes That May Be Responsible for the Unusual Resistances Exhibited by Bacillus pumilus SAFR-032 Spores

“…Further, it has been shown recently that in B. subtilis , the homologous recombination (HR) and non-homologous end joining (NHEJ) DNA repair pathways are needed for spore survival under proton radiation [50].…”

“…The α/β-type SASP, intact spore coat layers, reduced spore water content, DPA and spore pigmentation are the most important factors in determining spore survival and protection from mutagenic damage under simulated Mars conditions [49], [50]. All of the genes shown to be involved in these processes share >80% protein sequence identity between the three genomes as well as with the next nearest Bacillus relative.…”

Resistance of Bacillus subtilis Spore DNA to Lethal Ionizing Radiation Damage Relies Primarily on Spore Core Components and DNA Repair, with Minor Effects of Oxygen Radical Detoxification

“…X ray, proton, and Fe irradiations were conducted at the German Aerospace Center, Institute of Aerospace Medicine (DLR-ME), in Cologne, Germany, at the University of Florida Proton Therapy Institute (UF-PTI), Jacksonville, Florida, USA, and at the heavy ion medical accelerator (HIMAC) facility at the National Institute for Radiological Sciences (NIRS) in Chiba, Japan, respectively. Details on the irradiation geometry of the NIRS-HIMAC, DLR-ME, and UF-PTI facilities, beam monitoring, dosimetry, and dose calculations have been described (34)(35)(36)(37).…”

Water-soluble core/shell nanoparticles for proton therapy through particle-induced radiation

“…Although several-keV heavy-ion irradiation is efficient for mutation because of its high linear energy transfer (LET), the experiment should be done under vacuum environments, which cause severe damage to the experimental bacteria. Bacillus subtilis spores, which have shown resistance to extreme environments, were exposed to 218-MeV protons to study the effect of high-energetic proton irradiation on the spore survival [19].…”