Measurement of Fungi and Bacteria from Dust Collected on the International Space Station (ISS)

Exposure to fungi and bacteria can have important implications for human health. This is especially true on spacecraft, where astronauts may experience changes to their immune system. However, we do not understand how distribution of fungi and bacteria in different particle size fractions of dust in microgravity may impact human exposure. The goal of this work was to develop methods to characterize the microorganisms in different particle size fractions and in a passive sampler from dust collected on the International Space Station (ISS). Dust was analyzed from both a vacuum bag sample and a passive aerosol collector for both fungi and bacteria using DNA-based techniques. The passive aerosol sample consisted of a piece of double-sided black carbon sticky tape that was exposed to the air in ISS Node 3 for 16 days. We were able to obtain both bacterial and fungal DNA from both the passive sampler and the vacuum bag dust. To determine the percent recovery of cells and spores on the passive aerosol sample a 3 cm2 piece of black carbon tape was spiked with 10uL of Aspergillus fumigatus at a concentration of 2.164 x 106 spores/µL and 10µL of Bacillus atrophaeus at a concentration of 7.76 x 107 cells/µL. This spiked tape was extracted along with a blank sample of tape and a sample of A. fumigatus and B. atrophaeus. We divided the quantity of spores or cells recovered from the spiked tape sample by the amount recovered from the sample of A. fumigatus and B. atrophaeus and determined a 90% recovery of fungal spores and a 73% recovery of bacterial cells. Overall, we developed methods to analyze fungi and bacteria in dust from the ISS, which will be used in the HUMID study to consider microbial growth. Our results will have implications for future system design.