Growth-rate-dependent bacteriochlorophyll c/d ratio in the antenna of Chlorobium limicola strain UdG6040

The green sulfur bacterium Chlorobium limicola UdG6040 exhibited a signific ant change in the spectral properties of its antenna when transferred from batch culture to a sulfide-limited chemostat. In steady-state continuous cu ltures, the in vivo absorption maximum of the culture changed to shorter wa velengths according to the dilution rate. The maximum difference observed w as of 15 nm when cells were growing at 0.087 h(-1). HPLC analyses revealed that the observed spectral change was caused by a partial enrichment of the original BChl c-containing antenna with BChl d molecules together with a c hange in the homolog composition of both pigments. The relative amount of B Chl d reached a maximum value of 50% when cells were growing at 0.087 h(-1) . The content of BChl d decreased to less than the 22% when the dilution ra te was diminished to 0.015 h(-1). An unbalance of pigment synthesis at high dilution rates is suspected to be responsible of the changes observed in t he antenna composition. Chlorosomes isolated from Chl. limicola Ud6040 grow ing at 0.070 h(-1) contain organised pools of BChl c and BChl d in equal am ounts.