Adaptation ofBacillus subtilisCells to Archean-Like UV Climate: Relevant Hints of Microbial Evolution to Remarkably Increased Radiation Resistance

Abstract

In a precursory study for the space experiment ADAPT ("Molecular adaptation strategies of microorganisms to different space and planetary UV climate conditions"), cells of Bacillus subtilis 168 were continuously cultured for 700 generations under periodic polychromatic UV irradiation (200-400 nm) to model the suggested UV radiation environment on early Earth at the origin of the first microbial ecosystem during the Archean eon when Earth lacked a significant ozone layer. Populations that evolved under UV stress were about 3-fold more resistant than the ancestral and non-UV-evolved populations. UV-evolved cells were 7-fold more resistant to ionizing radiation than their non-UV-exposed evolved relatives and ancestor. In addition to the acquired increased UV resistance, further changes in microbial stress response to hydrogen peroxide, increased salinity, and desiccation were observed in UV-evolved cells. This indicates that UV-sensitive ancestral cells are capable of adapting to periodically applied UV stress via the evolution of cells with an increased UV resistance level and further enhanced responses to other environmental stressors, which thereby allows them to survive and reproduce under extreme UV radiation as a selection pressure.

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

“…target in biological systems (Hutchinson, 1985;Sutherland et al, 2000;Hada and Sutherland, 2006;Yokoya et al, 2008). Depending on the species analyzed, spores are up to 10 times more resistant than growing cells to ionizing radiation, whereas the magnitude of the difference in ionizing radiation resistance between spores and growing cells can be different at different types of ionizing radiation (Moeller et al, 2007;Horneck et al, 2010;Wassmann et al, 2010). DNA strand breaks are major lethal lesions in the genome of spores exposed to ionizing radiation (Micke et al, 1994).…”

Experimental evolution of Bacillus subtilis

“…Ultraviolet radiation Increased resistance to UV, X-rays, hydrogen peroxide (Wassmann et al, 2010;2012) …”

“…After 69 cycles -about 700 generations -each evolved population, but not the control, exhibited a 4.5-fold increase in UV resistance relative to the ancestor. All four populations simultaneously evolved increased resistance to X-rays, and two populations exhibited enhanced resistance to hydrogen peroxide (Wassmann et al, 2010). Strain MW01, an isolate from one of the evolved lines, was tested for UV resistance at five points in its life cycle: lag, exponential, and stationary phases; as mature endospores; and during germination.…”

Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond

“…Martian atmosphere and pressure even led to no detectable effect. When exposed to space or Mars UV, the spores were inactivated by 4.5 and 1-2 orders of magnitude respectively, showing that Martian environmental conditions are less harmful for these spores than space conditions (Wassmann et al 2010(Wassmann et al , 2011(Wassmann et al , 2012.…”