A long-living artificial tripartite symbiosis involving a green alga (Chlamydomonas), a bacterium (Azotobacter) and a fungus (Alternaria) was established on carbon- and nitrogen-free medium. The basis of the interdependence is the complementation of photosynthetic CO2 assimilation and atmospheric nitrogen fixation. Green color of the colonies indicated that the algal cells had enough nitrogen to synthesize chlorophylls. The chlorophyll content was nearly 40% of the control cells. The relatively high rate of photosynthetic oxygen evolution proved that nitrogen was effectively used for building up a well functioning photosynthetic apparatus. This was supported by the analysis of photosystems and ultrastructural investigations. In comparison with degreened algae cultured on nitrogen-free medium, the chloroplasts in the symbiont algal cells contained a well-developed, stacked thylakoid membrane system without extreme starch or lipid accumulation. The occurrence of the fungus in the association greatly increased the chlorophyll content. Far fewer types of amino acids were excreted by the tripartite cultures than by pure cultures. Cystathionine, which is a common intermediate in the sulfur-containing amino acid metabolism, was produced in high quantities by the tripartite symbiosis. This can mostly be attributed to the activity of the fungus.

• MeSH
• Alternaria growth & development   metabolism   physiology   MeSH
• Amino Acids metabolism   MeSH
• Azotobacter growth & development   metabolism   physiology   MeSH
• Chlamydomonas growth & development   metabolism   physiology   ultrastructure   MeSH
• Chlorophyll biosynthesis   MeSH
• Nitrogen metabolism   MeSH
• Nitrogen Fixation MeSH
• Photosynthetic Reaction Center Complex Proteins analysis   MeSH
• Photosynthesis MeSH
• Culture Media chemistry   MeSH
• Lipids analysis   MeSH
• Microscopy MeSH
• Carbon Dioxide metabolism   MeSH
• Starch analysis   MeSH
• Symbiosis * MeSH
• Microscopy, Electron, Transmission MeSH
• Thylakoids chemistry   ultrastructure   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Amino Acids MeSH
• Chlorophyll MeSH
• Nitrogen MeSH
• Photosynthetic Reaction Center Complex Proteins MeSH
• Culture Media MeSH
• Lipids MeSH
• Carbon Dioxide MeSH
• Starch MeSH