Occurrence of new bacteriochlorophyll d forms in natural populations of green photosynthetic sulfur bacteria

The presence of unusual bacteriochlorophyll (BChl) d forms in natural populations of green photosynthetic sulfur bacteria is reported. These new pigment forms share spectral properties with the standard BChl d previously described in green sulfur bacteria, i.e. absorption maxima at 429 nm and 656 nm at the Sorer and Q(y) bands, respectively, but greatly differ in the HPLC analysis. Two types of natural BChl d were found: type I. observed in populations of Pelodictyon clathratiforme and the green consortium 'Chlorochromatium aggregatum', was composed of three main homologs unevenly distributed along the chromatographic run. BChl d type II was only observed in photosynthetic communities dominated by Chloronema spp., and eluted as a cluster of seven homologs characterized by their high apolarity. The distinct chromatographic behavior suggests differences in the chemical structures of these pigments, which are suspected to be located at the C-17 position of the macrocycle by esterification of alcohols longer than farnesyl. The possible origin of these new pigment forms as well as their potential role in light adaptation in natural habitats is discussed. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.