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 m onitored during the stratification period of Coromina Lake, a freshwater, h olomictic pond of the Banyoles lacustrine area (Girona, NE Spain). The chro matographic analysis of this population revealed the presence of a wide var iety of both bacteriochlorophyll (BChl) d and BChl c homologues. Isolation of chlorosomes from cultured Pelodictyon cells and their further analysis b y steady-state fluorescence indicated that, although both pigment were pres ent in chlorosomes, only BChl c gave rise to an emission signal, suggesting a fast energy transfer from BChl d to BChl c. Likewise, chlorosomes isolat ed from natural samples were significantly larger (60-70 nm in width and 11 5-120 nm in length) than those isolated from cells grown in laboratory unde r 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 a re discussed in terms of the severe light limitation (available light inten sity <0.1 <mu>mol photons m(-2) s(-1) at the bacterial plate) under which t he population subsisted during the study period. (C) 2001 Federation of Eur opean Micro biological Societies. Published by Elsevier Science B.V. All ri ghts reserved.