Optimization of long-term storage procedures for the prebiotic cyanobacterium Arthrospira sp. As part of the MELiSSA (Micro-Ecological Life Support System Alternative) project

Arthrospira sp. is a well know prebiotic cyanobacterium due to its high protein concentration and is used as “superfood” in the form of food supplements under the name Spirulina. Thanks to these characteristics and its ability to produce oxygen by means of photosynthesis, Arthrospira sp. can be used as oxygen and food source. Therefore it is an excellent choice for the waste recycling system for long-term space missions (MELiSSA-project). Nowadays Arthrospira sp. can only be kept alive via sub-culturing. However this is not an optimal way of conservation due the high risk of contamination, possible genetic drift and human work load. A storage procedure for storing Arthrospira sp. in an dormant but reversal way is still to be discovered. For that purpose, diverse preservation methods were tested: Preservation in agar under different storage conditions; preservation using cryoprotectants like DMSO and trehalose; and preservation following metabolic conditioning such as nitrogen starvation and natural trehalose accumulation following salt stress. After each test, the cell integrity and cultivability were checked by microscopic imaging, including fluorescence microscopy, flow cytometry and sub-culturing. The main obtained results showed that preservation using 10% DMSO and 5% (or 10%) trehalose is effective for at least one week preservation at -80°C. To our knownledge, this is the first report of Arthrospira sp. being able to recover from a freezing step. Concerning metabolic conditioning before freezing, trehalose accumulation was successfully measured but, the final outcome of these experiments are is yet to come. On the other hand, nitrogen starvation preconditioning and the use of RNAlater were not convincing.