[Development of detection system of extraterrestrial microorganisms]

A noble method for the exploration of terrestrial and extraterrestrial soil microorganisms, especially targeted for Mars, has been developed. The method is based on the microscopic observation using fluorescence techniques. Microorganisms could be fluorescent by adsorption, enzymatic cleavage of extrinsic fluorescence chromophores such as acridine orange, ANS and SFDA, and also by intrinsic chromophores. The characteristic points of our fluorescence method are shown below. 1. The present method detected all the culturable cells tested (about 200 species from bacteria to eukaryofic cells). 2. Microorganisms in soil were much brighter than background fluorescence of soil. Cell shapes and location were clearly observed. 3. An esterase substatum SFDA, discriminated vital (reproductive) cells from dead. On the other hand, a membrane probe, ANS, detected both vital and dead cells. 3. Pre-treatment of cells with bleaching reagents improved the detection efficiency. Especially, this pretreatment was effecfive in Fungi with black chromophores. 4. Some anaerobic microorganisms such as methanogenic bacteria with intrinsic chromophores can be detected without stain. 5. Application of the technique to terrestrial soil revealed that more than 100 times larger cell density was obtained compared to the value obtained by the classic plate counting technique. Vertical distribution of microorganism of soil microorganisms from Mt. Shigayama showed that, at surface, cell density was small and maximum was shown below 15 cm from surface. 6. Some pre-biotic cell (cell like aggregates composed of amino acids) could be detected by SFDA or ANS. It can be concluded that the fluorescence technique is one of the most promising method for the exploration of extraterrestrial microorganisms.