ABSTRACT: This work presents the design and characteristics of a new compact ultraviolet (UV) irradiator used in a biological onboard space flight experiment. The experiment, called DRM, took place in the International Space Station research facility (ISS-13 expedition), during the Centenary Mission (Russian-Brazil) in March-April 2006. The DRM main objective was to correlate the DNA repair mechanism and mutagenesis with microgravity. A compact irradiator apparatus was designed for DRM to allow in situ induced radiation in space. This apparatus, called CIM, uses UV-A Light-emitting diodes (LEDs) with 375 nm wavelength as molecular lesions inducers on four bacterial E. coli strains. The manned space mission restrictions were focused on during the CIM main parts design. The ultraviolet dosimetry is also described in this document as DRM experiment results and the CIM operational data are reported to certify the CIM design and DRM protocol compatibility in space application.

Hydrogen peroxide is an important reactive oxygen species (ROS) that arises either during the aerobic respiration process or as a by-product of water radiolysis after exposure to ionizing radiation. The reaction of hydrogen peroxide with transition metals imposes on cells an oxidative stress condition that can result in damage to cell components such as proteins, lipids and principally to DNA, leading to mutagenesis and cell death. Escherichia coli cells are able to deal with these adverse events via DNA repair mechanisms, which enable them to recover their genome integrity. These include base excision repair (BER), nucleotide excision repair (NER) and recombinational repair. Other important defense mechanisms present in Escherichia coli are OxyR and SosRS anti-oxidant inducible pathways, which are elicited by cells to avoid the introduction of oxidative lesions by hydrogen peroxide. This review summarizes the phenomena of lethal synergism between UV irradiation (254 nm) and H2O2, the cross-adaptive response between different classes of genotoxic agents and hydrogen peroxide, and the role of copper ions in the lethal response to H2O2 under low-iron conditions.