Identification of volatile organic compound markers for bacterial growth in spacecraft wastewater

As humans move beyond low-Earth orbit, where resupply of water will be impractical or impossible, systems that can ensure the provision of safe, clean, recycled water are critical. Current methods of microbial detection for spacecraft water are crew time- and consumable-dependent and would not be possible during periods of dormancy. One potential method for microbial detection that can be performed remotely and without sample preparation is the analysis of headspace to determine if specific volatile organic compounds (VOC) are present. Here, the use of gas chromatography-mass spectrometry (GC-MS) to analyze the headspace above cultures of bacteria returned from the International Space Station is discussed. Three species of bacteria: Ralstonia pickettii, Burkholderia contaminans, and Klebsiella aerogenes, were cultured, and the VOCs emitted by each culture were analyzed through headspace GC-MS analysis. A number of species-specific compounds were detected, but a particular marker, dimethyl disulfide, was present in all species and test conditions. The isolates' genomes were sequenced, and genes encoding for enzymes that could contribute to the production of dimethyl disulfide were identified. This analysis supported the premise that each organism examined was capable of producing this compound as a byproduct of methionine metabolism and suggests that dimethyl disulfide would be a suitable target compound for the detection of process escapes in the area of microbial control in future spacecraft water recovery systems. The results shown here suggest that the use of MS-based techniques for headspace VOC analysis is a promising avenue for the detection of these common spacecraft bacteria in spaceflight wastewater.