Carbon metabolism of the cryptoendolithic microbiota from the Antarctic desert

The carbon metabolism of the cryptoendolithic microbiota of sandstones from the Ross Desert of Antarctica was studied in situ and in vitro. Organic and inorganic carbon compounds were metabolized by the microbiota, with bicarbonate incorporation into community lipids occurring primarily in the light. Light intensity affected the photometabolism of carbon with a photosynthesis-intensity response optimum at about 200 to 300 micromoles of photons per m2 per s. Photosynthesis was also affected by temperature, with a minimum activity at -5 degrees C, an optimum activity at 15 degrees C, and complete inhibition at 35 degrees C, indicating that the cryptoendolithic community was psychrophilic. The primary source of CO2 for photosynthesis in situ was the atmosphere. CO2 may also be photometabolized by using the carbon produced from respiration within the endolithic community. Photosynthesis occurred maximally when the microbiota was wet with liquid water and to a lesser extent in a humid atmosphere. This simple microbial community, therefore, exists under extremes of water, light, and temperature stress which affect and control its metabolism.