Nitrogen isotopic fractionation in the synthesis of photosynthetic pigments in Rhodobacter capsulatus and Anabaena cylindrica

Nitrogen isotopic discrimination was investigated for a purple nonsulfur bacterium. Rhodobacter capsulatus, during photoheterotrophic and photoautotrophic growth with N-2 and ammonia, and compared with nitrogen assimilation in a cyanobacterium. In R. capsulatus, the Delta N-15 values for biomass during growth with N-2 fixation and ammonia assimilation. relative to the N-source, ranged from -1.8 to -0.8 parts per thousand and -12.3 to -10.2 parts per thousand respectively. In the cyanobacterium, Anabaena cylindrica, the Delta N-15 value for biomass resulting from growth on molecular nitrogen was -0.8 to -1.7 parts per thousand relative to N-source. These values are similar to those observed for other microorganisms. Bacteriochlorophyll a in R. capsulatus was depleted in N-15 relative to biomass, whereas chlorophyll a in A. cylindrica was relatively enriched in N-15. (C) 2000 Elsevier Science Ltd. All rights reserved.