Effects of Heavy Ion Particle Irradiation on Spore Germination of Bacillus spp. from Extremely Hot and Cold Environments

Abstract

Extremophiles are optimal models in experimentally addressing questions about the effects of cosmic radiation on biological systems. The resistance to high charge energy (HZE) particles, and helium (He) ions and iron (Fe) ions (LET at 2.2 and 200 keV/µm, respectively, until 1000 Gy), of spores from two thermophiles, Bacillushorneckiae SBP3 and Bacilluslicheniformis T14, and two psychrotolerants, Bacillus sp. A34 and A43, was investigated. Spores survived He irradiation better, whereas they were more sensitive to Fe irradiation (until 500 Gy), with spores from thermophiles being more resistant to irradiations than psychrotolerants. The survived spores showed different germination kinetics, depending on the type/dose of irradiation and the germinant used. After exposure to He 1000 Gy, D-glucose increased the lag time of thermophilic spores and induced germination of psychrotolerants, whereas L-alanine and L-valine increased the germination efficiency, except alanine for A43. FTIR spectra showed important modifications to the structural components of spores after Fe irradiation at 250 Gy, which could explain the block in spore germination, whereas minor changes were observed after He radiation that could be related to the increased permeability of the inner membranes and alterations of receptor complex structures. Our results give new insights on HZE resistance of extremophiles that are useful in different contexts, including astrobiology.

Microbes from Brine Systems with Fluctuating Salinity Can Thrive under Simulated Martian Chemical Conditions

“…A phenomenon that has been observed in OD measurements of Bacillus sp. when they undergo the stressors of nutrient limitation [56][57][58][59][60]. For the strains that exhibited reduced growth in the higher fluid concentrations (Bacillus MKS3, Staphylococcus MKS13, Halomonas MKS19, Bacillus MKS28), this is possibly due to the changes in concentrations of salts or toxicity from some of the elements in the Rocknest fluid chemistry (e.g., Mn, Al, Fe; [61]) reaching concentrations that are inhibitory for the affected stains.…”

Effects of Ionizing Radiation and Long-Term Storage on Hydrated vs. Dried Cell Samples of Extremophilic Microorganisms

“…The GCRs are composed of high-energy protons, α-particles, and high atomic number nuclei and energy (HZE) ions that in turn represent about 1% of GCRs and are the major cause of the lethal effects of this radiation. The biological effects produced by an HZE have been extensively studied in a variety of space experiments or on ground simulation facilities using the biological dosimeter spores of Bacillus subtilis species [2][3][4][5]. These studies showed that the ionizing radiation effects depend upon both the delivered dose and the type of radiation; indeed, the LET value directly correlates with the number of changed cell structures and molecules that are passed through the particle's path [2][3][4][5].…”

“…The biological effects produced by an HZE have been extensively studied in a variety of space experiments or on ground simulation facilities using the biological dosimeter spores of Bacillus subtilis species [2][3][4][5]. These studies showed that the ionizing radiation effects depend upon both the delivered dose and the type of radiation; indeed, the LET value directly correlates with the number of changed cell structures and molecules that are passed through the particle's path [2][3][4][5]. Fe, Ar, and He ions are high-LET particles (>2 keV/mm), and they can be harmful by means of two different processes, i.e., "direct hits" and "indirect hits": in the first case, the cell is in the track core of the HZE particle, and it is passed via the particle; in the second case, the cell is hit only by high-energy secondary electrons, i.e., δ-rays, which are produced by interaction of the HZE with the biological target.…”

“…Moreover, when radiation passes through a biological target, two types of interaction can take place: a direct radiation effect, i.e., direct energy absorption by DNA, proteins, and other cellular components; an indirect radiation effect, i.e., interaction of cellular targets with radicals generated by radiolysis of water, i.e., the so-called reactive oxygen species (ROS) [2,4], or other chemical species [2]. In January 2018, we had the opportunity to participate in the "STARLIFE" project [4], an international intercomparison radiation campaign that studied the effect of ionizing radiations on different biological model systems relevant to astrobiology [3,4]. To identify new microbial species that potentially could resist space radiation and to test microorganisms that could be used for real space exposure, we proposed using two extremophilic microorganisms belonging to both the Archaea and Bacteria domains that, in our previous studies [6][7][8], showed promising resistance to multiple extreme parameters mimicking the space environment as biological samples.…”

Extant Earthly Microbial Mats and Microbialites as Models for Exploration of Life in Extraterrestrial Mat Worlds

“…These modern-day mat ecosystems resemble life during the Precambrian era, when the biosphere was mostly microbial and benthic [ 5 , 6 , 7 , 8 ]. Fortunately, even today, microbial mats similar to life in the shallow, anoxic, sometimes euxinic (high hydrogen sulfide, low dissolved oxygen) seas of the early biosphere thrive in several globally distributed refugia under extreme conditions of moisture, salinity, pH, temperature, and oxygen [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. Indeed, a great variety of living microbial mats with a diversity of structural and functional characteristics are found in extant extreme ecosystems all over the world ranging from subglacial lakes to deep sea thermal vents [ 14 ].…”