IMMUNOLOGICAL AND ULTRASTRUCTURAL CHARACTERIZATION OF THE PHOTOSYNTHETIC COMPLEXES OF THE PROCHLOROPHYTE PROCHLOROCOCCUS (OXYCHLOROBACTERIA)

Authors

  • Christiane Lichtlé,

    Corresponding author
    1. Laboratoire de Photorégulation et Dynamique des membranes végétales. Ecole Normale Supérieure, Centre National de la Recherche Scientifique URA 1810, 46 rue d'Ulm, 75230 Paris Cedex 05, France
      2 Author for reprints requests.
    Search for more papers by this author
  • Jean Claude Thomas,

    1. Laboratoire de Photorégulation et Dynamique des membranes végétales. Ecole Normale Supérieure, Centre National de la Recherche Scientifique URA 1810, 46 rue d'Ulm, 75230 Paris Cedex 05, France
    Search for more papers by this author
  • Agnès Spilar,

    1. Laboratoire de Photorégulation et Dynamique des membranes végétales. Ecole Normale Supérieure, Centre National de la Recherche Scientifique URA 1810, 46 rue d'Ulm, 75230 Paris Cedex 05, France
    Search for more papers by this author
  • Frédéric Partensky

    1. Station Biologique, Centre National de la Recherche Scientifique GDR 869 et Université Paris VI, BP 74, 29682 Roscoff, France
    Search for more papers by this author

2 Author for reprints requests.

ABSTRACT

Ultrastructural features and immunological properties of some thylakoid proteins were examined in two strains of the prochlorophyte Prochlorococcus and compared to those of other photosynthetic prokaryotes and eukaryotes. Both strains exhibited two or three rows of tightly appressed thylakoidal membranes, located at the cell periphery. However, thylakoids were concentrically arranged in the strain from the Sargasso Sea (SARG) and horseshoe-shaped in the Mediterranean isolate (CCMP 1378). Although lacking phycobilisomes, both cell types shared with cyanobacteria the presence of carboxysome-like structures and glycogen granules as storage compounds.

The main thylakoid polypeptides separated by sodium dodecyl sulfate—polyacrylamide gel electrophoresis were characterized by Western blotting using several antibodies. The 30-kDa polypeptide of the light-harvesting complex (LHC) of Prochlorococcus showed a weak positive immunological cross-reaction with an antibody raised against the 32-kDa apoprotein of the LHC of the prochlorophyte Prochlorothrix hollandica. In contrast, it showed no immunological relationships with the chlorophyll a/b (Chl a/b) LHCs of green algae and higher plants. Protein membranes from Prochlorococcus strongly cross-reacted with antibodies raised against reaction center polypeptides of photosystems II and I (PSs II and I) of other photosynthetic organisms, confirming the high degree of conservation of these basic compounds of the photosynthetic machinery during evolution. Immunolocalization of thylakoid proteins showed that the LHC proteins, the major PS II reaction center proteins (CP 43 and D2), and the PS I reaction center proteins were equally distributed within the thylakoid membranes in contrast to the segregation observed in higher plants and green alga thylakoids. We also identified ribulose-1, 5-bisphosphate carboxylase/oxygenase in the carboxysomes. These results suggest that Prochlorococcus is more closely related to cyanobacteria than to green plastids even though it contains Chl b.

Ancillary