Variability of the photosynthetic antenna of a Pelodictyon clathratiforme population from a freshwater holomictic pond

A population of the green sulfur bacterium Pelodictyon clathratiforme was monitored during the stratification period of Coromina Lake, a freshwater, holomictic pond of the Banyoles lacustrine area (Girona, NE Spain). The chromatographic analysis of this population revealed the presence of a wide variety of both bacteriochlorophyll (BChl) d and BChl c homologues. Isolation of chlorosomes from cultured Pelodictyon cells and their further analysis by steady-state fluorescence indicated that, although both pigment were present in chlorosomes, only BChl c gave rise to an emission signal, suggesting a fast energy transfer from BChl d to BChl c. Likewise, chlorosomes isolated from natural samples were significantly larger (60-70 nm in width and 115-120 nm in length) than those isolated from cells grown in laboratory under optimal light conditions (48 +/-6.8 mn and 100 +/- 15.8 nm. in width and length, respectively). The potential role of heterogeneous BChl c- and BChl d-containing chlorosomes and the differences in chlorosome size measured are discussed in terms of the severe light limitation (available light intensity <0.1 mol photons m(-2) s(-1) at the bacterial plate) under which the population subsisted during the study period. (C) 2001 Federation of European Micro biological Societies. Published by Elsevier Science B.V. All rights reserved.