Preliminary characterisation of the photosynthetic bacterium Rhodospirillum rubrum ATCC25903 by means of phenotypic and molecular methods

ESA's Micro-Ecological Life Support System Alternative (MELiSSA) project targets to equip spaceship with a bioregenerative self-sustaining loop of bioreactor able to deal with air, water, food and waste management. Because the organisms inhabiting the MELiSSA loop have to perform their task as optimally as possible, the bacteria and higher plants inhabiting it, have to be characterised in every detail in order to detect any potential functioning problem that could be encountered within the loop during long haul space missions. The present study allowed us to acquire the bases necessary to pursue more in depth investigations of R. rubrum ATCC25903 response to environmental stress conditions. Culture conditions that allow optimal growth of R. rubrum in liquid culture both in light anaerobic and dark aerobic culture conditions have been defined. A differential protein extraction protocol has been finalised to perform the study of the whole proteome of R. rubrum and to construct 2D-protein maps. In addition, our work on the protocol for DNA extraction and AFLP analysis, though not optimised yet, gave us a good first insight into the technique. Proteomic analysis of space samples from MESSAGE 2 experiment suggests that there is a differential response between ground and space conditions (up and down protein regulation). Likewise, from the analyses of replicaplating (done immediately after the space samples returned back to Earth) one consistent observation came out: tellurium seems to allow growth in space condition and enhanced tellurium resistance is observed in space samples grown in 869 light anaerobic condition. Further proteomic and genotypic (DNA, RNA) analyses are foreseen to characterise the response of R. rubrum to space environmental conditions. Finally, preliminary ground-based modeled microgravity experiments using the Rotary Cell Culture System showed no difference in growth kinetics of R. rubrum between low shear modelled microgravity and control conditions. However, absence of impact on growth parameters does not mean that there is no effect on the metabolism of the organism. This will have to be investigated by performing proteomic and genotypic (DNA, RNA) analyses.