Susceptibility of microbes to far-UVC light (222 nm) on spacecraft and cleanroom surfaces

ABSTRACT Far-UVC light (222 nm) is an emerging decontamination tool with potential for spacecraft assembly applications due to its strong germicidal efficacy and minimal risk to human health. This study evaluated the susceptibility of three UV-resistant microbial species, Deinococcus radiodurans and Bacillus subtilis as vegetative cells and Bacillus pumilus as spores, across eight spacecraft and cleanroom-relevant materials with varying surface properties, including contact angle, reflectivity, and roughness. While D. radiodurans demonstrated the highest overall resistance to far-UVC, material properties significantly influenced its inactivation rate (k 1 [cm 2 /mJ]), and its susceptibility varied significantly by surface. No significant relationship between material properties influencing k 1 values was observed for B. subtilis and B. pumilus . Collectively, these findings highlight far-UVC as a robust and practical bioburden reduction tool capable of inactivating resistant microbes regardless of material surface characteristics. IMPORTANCE This study builds upon previous research on the inactivation of hardy bacteria and spores using far-UVC light by evaluating the susceptibility of microbes to far-UVC light across a range of surface materials. By focusing on hardy organisms and diverse substrates, this work provides critical insights into the practical applications of far-UVC technology in complex environments. Microbial disinfection is a key component of planetary protection, ensuring that space exploration activities do not inadvertently transport terrestrial organisms to extraterrestrial environments. These findings demonstrate that far-UVC is effective across materials with varying properties and can serve as an effective alternative for bioburden reduction that can be safely operated in occupied spaces.