Photosynthesis, Nitrogen Fixation and Enzyme Activities in Chlamydomonas-Azotobacter Symbioses

Abstract

Summary Nitrogen-fixing associations were established by mixing Azotobacter and Chlamydomonas cells and were cultured on nitrogen and carbohydrate free media. Scanning electron micrographs show a few bacteria localized on the surface of the algal cells. The rate of the photosynthetic 02-evolution in symbioses is nearly the same as the value obtained with the control. Acetylene reduction assay showed that nitrogen fixation was detectable in associative symbioses. GS, ATP-ase, Diaphorase and IDH activities were studied by polyacrylamide gel electrophoresis in Chlamydomonas reinhardii, Azotobacter chroococcum, A. beijerinckii, A. agilis, A. vinelandii and Chlamydomonas-Azotobacter symbioses. The mobility of GS enzymes is the same in algae and bacteria, but ATP-ase migrates faster in the case of Azotobacter. The enzyme pattern of alga-bacterium symbioses is similar to that found in Chlamydomonas. IDH has no activity in Chlamydomonas, but shows high activity in Azotobacters. An enzyme with lower molecular weight is present in alga-bacterium symbioses. Diaphorase isoenzymes are different in alga and bacterium cells. In the symbioses, the enzyme are partially similar to algae, but an enzyme of lower molecular weight also exists. The results show that there is an interaction at the biochemical level between the two organisms associated.