Storage Products in Purple and Green Sulfur Bacteria

Summary

Synthesis and accumulation of storage materials occurs in phototrophic sulfur bacteria under virtually all environmental conditions. After summarizing the general characteristics of the different storage products and the maximum contents at which they are found in different organisms, attention is paid to the environmental conditions which affect their accumulation. Although the specific contents are usually high when resources are present in excess, deposition also occurs under conditions of limitation, thus suggesting a strategy which maximizes long term benefit in a fluctuating environment, rather than instantaneous growth. The physiological role of storage products is illustrated through several laboratory experiments, some were fluctuations play a major role, and later on, in a section which describes field situations which actually confirm several of the previous experimental results. The chapter ends with a section which emphasizes the physical effects of the deposition of storage products specially in organisms with a planktonic way of life. Changes in cell size and density derived from the presence of storage structures are discussed, specially in relation to their impact on buoyancy regulation and sinking rates.