Towards an in-situ endospore detection instrument

Bacterial spores (endospores) are the most resilient form of life and as a result have been invoked as the most likely candidates capable of surviving interplanetary travel. We are designing an in situ instrument to detect and quantify endospores in extreme environments, including Martian environments (i.e., Mars endospore detector, MED). Our detection strategy is based on a chemical marker (dipicolinic acid, DPA), which is unique to bacterial spores, highly concentrated (0.1-1 moles per liter within the spore), and readily detected with a number of spectroscopic methods. In an effort to evolve an in situ instrument design, we are evaluating various extraction and detection protocols for endospores in soils. In general, the protocols consist of endospore lysis (i.e., rupture of cell) to release DPA, extraction of DPA from spores and soil, purification of the extract, and quantification of DPA in terms of spores/gram. Here we report extraction efficiencies and limits of detection for endospores embedded in lab sand, soil from JPL grounds, and soil from the Atacama Desert (Chile) for three protocols: spore lysis by autoclaving followed by aqueous extraction of DPA with (1) UV absorbance spectral determination of DPA or (2) ion chromatography coupled with inline UV absorbance detection of DPA, and (3) spore lysis by acid treatment followed by sublimation extraction of DPA with terbium-DPA luminescence detection.