Evaluating Quantitative Measures of Microbial Contamination from China's Spacecraft Materials.

Different methods are used for the quantification of microbial load on spacecrafts. Here, we investigated a number of methodologies currently in use with the intent to identify the most accurate methods for the quantification of microbes on low-biomass metal surfaces such as those used in China's Space Station. In a previous study, we observed a high abundance of Bacillus sp. TJ 1-1 on interior surfaces of China's Space Station, and we therefore undertook this study in which we used a range of 102 to 109 cells/100 cm2 of this strain for setting different contamination levels. Four of the most common analytical approaches (contact plate, spread plate, quantitative PCR, and BacLight™) were used to quantify the number of viable microbial cells associated with the materials of China's Space Station. Results show that, for 102 cells/100 cm2, the contact plate method is the most convenient and reliable. For microbial contamination levels ≥103 cells/100 cm2 and a sampling area of 121 cm2, the BacLight method proved to be most reliable for the detection of live cells. Moreover, a sampling area of 121 cm2 was found to be the most suitable for analysis of metal surfaces for space station interiors, which are usually low in biomass. These results establish suitable sampling and processing methodologies for microbial enumeration of metal surfaces on China's Space Station.

Microbiomes of China's Space Station During Assembly, Integration, and Test Operations.

Sufficient evidence indicates that orbiting space stations contain diverse microbial populations, which may threaten astronaut health and equipment reliability. Understanding the composition of microbial communities in space stations will facilitate further development of targeted biological safety prevention and maintenance practices. Therefore, this study systematically investigated the microbial community of China's Space Station (CSS). Air and surface samples from 46 sites on the CSS and Assembly Integration and Test (AIT) center were collected, from which 40 bacteria strains were isolated and identified. Most isolates were cold- and desiccation-resistant and adapted to oligotrophic conditions. Bacillus was the dominant bacterial genus detected by both cultivation-based and Illumina MiSeq amplicon sequencing methods. Microbial contamination on the CSS was correlated with encapsulation staff activities. Analysis by spread plate and qPCR revealed that the CSS surface contained 2.24 × 103-5.47 × 103 CFU/100 cm2 culturable bacteria and 9.32 × 105-5.64 × 106 16S rRNA gene copies/100cm2; BacLight™ analysis revealed that the viable/total bacterial cell ratio was 1.98-13.28%. This is the first study to provide important systematic insights into the microbiome of the CSS during assembly that describes the pre-launch microbial diversity of the space station. Our findings revealed the following. (1) Bacillus strains and staff activities should be considered major concerns for future biological safety. (2) Autotrophic and multi-resistant microbial communities were widespread in the AIT environment. Although harsh cleaning methods reduced the number of microorganisms, stress-resistant strains were not completely removed. (3) Sampling, storage and analytical methods for the space station were thoroughly optimized, and are expected to be applicable to low-biomass environments in general. Microbiology-related future works will follow up to comprehensively understand the changing characteristics of microbial communities in CSS.

Detection of Fungi from Low-Biomass Spacecraft Assembly Clean Room Aerosols.

Highly sensitive and rapid detection of airborne fungi in space stations is essential to ensure disease prevention and equipment safety. In this study, quantitative loop-mediated isothermal amplification (qLAMP) was used to detect fungi in the aerosol of the low-biomass environment of China's space station assembly clean room (CSSAC). A qLAMP primer set for detecting a wide range of aerosol fungi was developed by aligning 34 sequences of isolated fungal species and 17 space station aerosol-related fungal species. Optimization of sample pretreatment conditions of the LAMP reaction increased the quantitative results by 1.29-1.96 times. The results showed that our qLAMP system had high amplification specificity for fungi, with a quantifiable detection limit as low as 102. The detected fungal biomass in the aerosol of CSSAC was 9.59 × 102-2.20 × 105 28S rRNA gene copy numbers/m3. This qLAMP assay may therefore replace traditional colony-forming unit and quantitative PCR methods as an effective strategy for detecting fungi in space stations.