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The relative content of the four main bacteriochlorophyll (BChl) e homologs of several populations of brown-colored photosynthetic sulfur bacteria grown in different waterbodies have been measured by high performance liquid chromatography and statistically compared by principal component analysis. All the studied populations possessed representative pigment patterns enriched in highly alkylated bacteriochlorophyll e homologs, with average contents of 0.02±0.01%, 24.92±1.01%, 35.2±0.70%, and 39.9±0.71% for bacteriochlorophyll e1, e2, e3, and e4, respectively. These values clearly differ from those obtained for the same species growing under optimal conditions in laboratory batch cultures (4.99±1.11%, 50.34±1.73%, 28.99±0.63%, and 15.6±1.10% for bacteriochlorophyll e1, e2, e3, and e4, respectively). Multivariate statistical analyses grouped samples into two main clusters, both related to the developmental state of the population. Within these clusters, samples were arranged in several groups according to the physiological pigment response of bacterial populations to light limitation. Although bacteriochlorophyll homolog distribution cannot be considered a real taxonomic character, the data presented demonstrate that it can be useful in field studies since it reflects both the physiological status of the cells and the light regime under which the population has been growing.

The annual limnological dynamics of two meromictic basins of Lake Banyoles (C-III and C-IV) have been studied and compared on the basis of their physical, chemical and biological characters. Stability values calculated for both basins gave 865 g cm cm−2 and 495 g cm cm−2 for C-III and C-IV respectively. These values are in agreement with the fact that C-IV was almost completely mixed during winter. In this basin, during stratification, the monimolimnion increased in thickness as the stability increased. Isolation of the respective monimolimnia resulted in the development of anoxic conditions and the accumulation of sulphide in both C-III and C-IV, which favoured the development of dense populations of sulfur phototrophic bacteria. The purple sulphur bacterium Chromatium minus and the green sulphur bacterium Chlorobium phaeobacteroides were identified as the main components of these photosynthetic populations. The different depths at which the O2/H2S boundary was situated in both basins (and consequently the different light intensity reaching this zone) determined the growth of these bacteria. Light intensities at the chemocline of C-IV reached values up to 5% of surface incident light. In contrast, in C-III this variable was sensibly lower, with values depending on season and seldom reaching 1%. Phototrophic bacteria were consequently found earlier in C-IV than in C-III, where no significant concentrations were found until August. Finally stability is discussed as an important factor controlling chemical and biological dynamics in meromictic lakes.

The ecological succession of two microbial planktonic populations in the chemocline of C-IV, a meromictic basin of Lake Banyoles has been studied during the stratification period of 1989 (June to October). A dense population of deep-living algae Cryptomonas phaseolus was found growing between 13 and 14 meters depth, forming peaks of 10 to 20 μg.l−1 of chlorophyll a. The physical and chemical properties of the water were continually changing during the studied period and were strongly related to the biological processes developed at the monimolimnion of C-IV. Although the monimolimnion of the basin was initially anoxic (Eh values were around +300 mV and sulphide was not present at detectable levels) soluble iron and sulphide appeared sequentially, displacing the deep-living algae population and setting the conditions for the development of a population of brown Chlorobiaceae, Chlorobium phaeobacteroides. Although Cryptomonas population abandons the chemocline (13.75 m.) and decreases its biomass, it does not disappear at all, but moves upwards (8–11 m.) leaving the zone to sulphur phototrophic bacteria which find optimal conditions to grow. The sulphide diffusion coming from sediment and the nutrient limitation were the main responsible factors accounting for the upwards migration and the decrease of growth rate of the algal population respectively.

A reversed-phase High Performance Liquid Cromatography (HPLC) method has been developed to accurately separate bacteriochlorophyllsc, d ande homologues in a reasonably short run time of 60 minutes. By using this method, two well-defined groups of bacteriochlorophyll homologue peaks can be discriminated. The first one consists of 4 peaks (min 24 to 30), which corresponds to the four main farnesyl homologues. The second peak subset is formed by a cluster of up to 10 minor peaks (min 33 to 40). These peaks can be related with series of several alcohol esters of the different chlorosome chlorophylls. The number of homologues was, however, quite variable depending on both, the bacteriochlorophyll and the bacterial species. The method hereby described, also provides a good separation of other photosynthetic pigments, either bacterial (Bacteriochlorophylla, chlorobactene, isorenieratene and okenone) or algal ones (Chlorophylla, Pheophytina and β-carotene). A preliminary screening of the homologue composition of several green photosynthetic bacterial species and isolates, has revealed different relative quantitative patterns. These differences seem to be related to physiological aspects rather than to taxonomic ones. The application of the method to the study of natural populations avoids the typical drawbacks on the pigment identification of overlapping eukaryotic and prokaryotic phototrophic microorganisms, giving further information about their physiological status.

The microbial ecology of the filamentous phototrophic bacterium, Chloronema giganteum, has been studied in the water column of three central European lakes (Schiein, Buchen and Vechten). In these lakes an anoxic layer, termed the transition zone, was located between the oxycline and the redoxcline. The migration capacity of Chloronema through this zone appears to be responsible for the natural preponderance of either straight or spiral forms. When the transition zone is less than 1 m thick the straight form is dominant, but when this transition zone is wider than 2 m the spiral form is enriched. The intermediate situations favour both filamentous forms.

The annual dynamics of the phototrophic bacterial populations developing in the anoxic layers has been monitored in three basins of the northern area of Lake Banyoles (Spain). Although two of the studied basins are meromictic and one is holomictic, chemical properties of the water are almost identical. Therefore, differences in both the spatial and temporal distribution, as well as in the composition of phototrophic bacterial communities, dominated by Chlorobium phaeobacteroides and Chromatium minus, are discussed on the basis of the structural and morphometric characteristics of each basin. Both species showed the same physiological adaptations to light intensity changes by modifying the carotenoid/bacteriochlorophyll ratio. Light reaching the oxic-anoxic boundary appears to be the most important factor controlling the growth of phototrophic bacteria in Lake Banyoles. The oxic-anoxic boundary becomes shallower as summer advances, until enough light is available for bacterial photosynthesis.