SURVIVAL AND GROWTH OF COMMON CYANOBACTERIA IN PRIMORDIAL AND EXTRATERRESTRIAL ATMOSPHERES

Life appeared on Earth as early as 3.5 billion years ago. At this time, Earth's atmosphere probably consisted of nitrogen and carbon dioxide with no free oxygen. During this same period, Mars may have had a thicker atmosphere than it does at present, which primarily consisted of carbon dioxide with some nitrogen and argon. Many researchers have hypothesized that life may have arisen on Mars at roughly the same time that it did on Earth. We have successfully grown four strains of freshwater cyanobacteria under atmospheric conditions resembling those of primordial Earth (20% CO₂): Anabaena sp., Synechococcus PCC7942, Synechocystis 6803 and Plectonema boryanum UTEX485. We also found that Plectonema boryanum grows (slowly) under a hypothesized primordial martian atmosphere of 100% CO₂. During exposure to increased CO₂ levels, damage occurs to the photosynthetic electron transport (PET) apparatus. In general, damage to PET is more severe in unicellular cyanobacteria than in filamentous cyanobacteria. We are also investigating the physiology and evolution of the antioxidant system under primordial conditions by growing wild-type and sodB^- (Fe superoxide dismutase) mutants of Synechococcus PCC7942 in an atmosphere of 2.5% CO₂ in N₂. Preliminary results indicate that the FeSOD has no physiological benefit under anoxic conditions. This suggests that oxygenic photosynthesis could have evolved before the appearance of antioxidant systems. Additional results from current experiments will be also presented. (This research is supported by grants from the Arkansas Space Grant Consortium, and the NASA Institute for Advanced Concepts.)