Tersicoccus phoenicis (Actinobacteria), a spacecraft clean room isolate, exhibits dormancy

Space missions or spacecraft equipment destined for sensitive environments, such as Mars, Europa, or Enceladus, are required to be designed to avoid forward contamination. Spacecraft are assembled in clean rooms (SACs) employing treatments to eliminate microbial contamination. However, some organisms can survive the cleaning procedures. Characterization of these populations, through both culture-based and sequencing methods, reveals that the majority consists of spore-forming bacteria. However, a smaller group of non-spore-forming organisms, primarily classified within the order Micrococcales of the phylum Actinobacteria (Actinomycetota), exists in some SACs. Despite their repeated occurrence and isolation, actinobacterial strains associated with SACs have not been studied for their dormancy potential. Here, we show for the first time that a non-spore-forming SAC isolate, Tersicoccus phoenicis (Micrococcales), enters dormancy under nutrient starvation. Dormancy in Micrococcus luteus involves a universal stress protein and a resuscitation-promoting factor (Rpf). Genes for these proteins are widely found in actinobacteria, including T. phoenicis. We show that dormant T. phoenicis (Micrococcales) can be revived through the addition of the Rpf to the media. Dormancy, as observed in the SAC actinobacterial isolate T. phoenicis, could well be a common trait adopted by other actinobacterial strains under the stressful conditions of spacecraft clean rooms or the ISS (International Space Station). This has implications for the persistence, identification, and recovery of such microbes from cleanroom facilities.IMPORTANCENASA's long-range goal of a human mission to the Mars surface raises issues relating to planetary protection. The concerns of forward contamination require that spacecraft assembly clean rooms (SACs) be maintained to inhibit microbial survival. However, despite these efforts, distinct microbial communities persist. Here, we show that a SAC isolate, T. phoenicis, exhibits dormancy, a state in which the cells are viable but not cultivable. Dormancy may help non-spore-forming organisms survive in the clean room environments utilized for space missions. This has implications for improving cleaning procedures.