Resistivity of Spores to Ultraviolet and γ Radiation while Exposed to Ultrahigh Vacuum or at Atmospheric Pressure1

Abstract

Viability studies were conducted on microbial spores subjected to ultrahigh vacuum (UHV) in the 10-9 to 10-10 torr range. After 5 to 7 days in vacuum, they were exposed to ultraviolet (UV) or to y radiation either while still under vacuum or in the presence of dried air. Among the four test organisms subjected to UHV and ultraviolet radiation, Aspergillus niger was the most resistant; Bacillus megaterium, B. subtilis var. niger, and B. stearothermophilus were about equally less resistant. All four spores were more sensitive to ultraviolet radiation when UHVdried than when desiccant-dried. Of the four test organisms subjected to UHV and y radiation, B. megaterium proved to be the most resistant; A. niger was the least resistant; and the remaining two organisms were of intermediate resistivity. All four organisms were less radiation resistant when UHV-dried than when irradiated in their normally hydrated state, and all showed an increased radiosensitivity after vacuum drying when oxygen was present. In addition, spores of B. subtilis var. niger and A. niger were less radiosensitive when UHV-dried and irradiated in vacuum than when "wet" and irradiated in air, whereas the reverse relationship was observed for the remaining two organisms. Based on the fact that microbial contaminants can be readily shielded from UV light by soils, metal particles, etc., and considering that the levels of ionizing radiations reported to be present in interstellar space are generally lower than those used in these experiments, the decrease in radioresistivity imparted by UHV drying is not of a sufficient magnitude to sterilize dependably portions of a spacecraft while on a mission.

Isolation and characterization of a novel γ‐radiation‐resistant bacterium from hot spring in Iran

“…Our data clearly indicates that the isolated novel mesophilic bacteria B. megaterium WHO is highly resistant to radiation ( Fig. 4) in such a way that one percent of the cell population has survived with 22 KGy radiations, while the required dose for inactivation of B. megaterium is approximately 5.9 KGy [2]. Our strain also shows stronger resistance to gamma-radiation than B. megaterium.…”

“…niger, and B. stearothermophilus Correspondence: Hossein Naderi-Manesh, Department of Biochemistry, Faculty of Science, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran E-mail: naderman@modares.ac.ir subjected to UV and γ-radiation, B. megaterium appeared to be the most resistant, and requiring 400,000 rad (1 kGy = 10 5 rad) for over 99% destruction [2]. Ionizingradiation-resistant organisms have been isolated from a wide range of environments, including sawdust [3], sewage [4], paper mill machinery [5,6], animal feeds processed meat [7], dried food [8 -10], feather pillows [11], textiles, irradiated meat and fish [12], thermally polluted water [13], and irradiated rice [14].…”

Aspergillus niger Spores Are Highly Resistant to Space Radiation

“…This result is unexpected, as the presence of water is known to decrease radiation resistance via ROS formation. Nevertheless, A. niger spores have previously been shown to have increased radiation sensitivity when vacuum-dried and irradiated in air compared to wet spores irradiated in air (Silverman et al, 1967). However, the same study reported that vacuum-dried spores irradiated in vacuum were found to be more resistant to radiation, which implies that space vacuum desiccation might increase A. niger spore resilience (Silverman et al, 1967).…”

“…Nevertheless, A. niger spores have previously been shown to have increased radiation sensitivity when vacuum-dried and irradiated in air compared to wet spores irradiated in air (Silverman et al, 1967). However, the same study reported that vacuum-dried spores irradiated in vacuum were found to be more resistant to radiation, which implies that space vacuum desiccation might increase A. niger spore resilience (Silverman et al, 1967). Interestingly, a study assessing the impact of water in radiation resistance of yeast reports that small amounts of water substantially increases radiation sensitivity (Hutchinson et al, 1957).…”

“…A. niger spores are highly pigmented and can be easily dispersed through the air which facilitates habitat colonization. Also, as an opportunistic human pathogen, inhalation of A. niger spores can lead to human respiratory infections (Silverman et al, 1967;Latgé, 1999;Esbelin et al, 2013). Thus, the ability of A. niger to survive and grow in the spaceflight environment is a potential threat to both astronaut health and spacecraft safety.…”