Photosynthetic bacteria early development

It is a matter of conjecture as to whether sunlight was involved in the buildup of early organic molecules which eventually formed DNA, RNA and proteins. Photosynthetic bacteria may well have been the very first independent life forms, and from the time of the growth of green plants the atmosphere must have become gradually richer in oxygen, since it appears as a byproduct in the major process of photosynthesis. It is generally accepted that early life developed in the oceans, and it may be surmised that its eventual development on land was made possible by the formation of the protective ozone layer in the upper atmosphere. 

Thus, the appearance of free sulfate does not require the advent of free oxygen in the Archean environment. Certainly sufficient free sulfate had appeared in the hydrosphere prior to development of the pathway of dissimilatory sulfate reduction. Schidlowski (1979) argues that the small fractionations observed between sulfide and sulfate 834s values of pre-2.7 billion year rocks (Figure 10.11) are consistent with the hypothesis that the oxidation of sulfide to sulfate by photosynthetic bacteria preceded the bacterial pathway of dissimilatory sulfate reduction and may have been responsible for early free dissolved sulfate concentrations in the hydrosphere. 

Fig. 2. An evolution diagram illustrating a suggestion of common ancestry of some present-day organisms. The essential features of present-day photosynthesis may have originated in the prebiotic era and is preserved in its most primitive form in (at least some) present-day phototrophs. The heterotrophs may have developed parallel with the aerobic nonphotosynthetic bacteria, some l to 1.5 x 109 years after the emergence of the cyanobacteria. The eukaryotic photosynthetic organisms developed much later, perhaps some 1.5 to 0.5 x 109 years ago. The archaebacteria are primitive organisms that seem to have no evolutionary relation with the present prokaryotes.21 Little is known about their energy metabolism. Tentatively, they are considered as a very early form of cellular life.

Another experimental approach to the study of sulfureta in sediments was devised by Hallberg et al. (1976). Closed plexiglass boxes (Schippel et al., 1973) equipped with sampling ports and electrodes for continuous measurement of pH, Eh and sulfide-ion activity are anchored in soft bottom sediments, and physical, chemical and biological characteristics of the sediment-water system monitored over a period of time. In a 9-month experiment on Baltic Sea sediments, sulfate reduction proceeded rapidly in the early stages followed by sulfide reoxidation due to the development of the photosynthetic sulfur bacteria Chromatium and Chlorobium. 

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