Saline habitats

Chloridoideae are adapted to stressful arid or saline habitats (sand dunes, coastal marshes, semi-deserts). Their widespread distribution with the radiation center in South Africa suggests that they acquired the C4 photosynthesis and expanded before the breakup of the Pangea (Middle Cretaceous). 

Microbial polysaccharides are classified as (a) cell wall polysaccharides, (b) intracellular polysaccharides, and (c) extracellular polysaccharides. The first two are integral part of the cell, while exopolysaccharides are produced by numerous microorganisms, many of which are isolated from aquatic, especially marine ecosystems. About 134 strains have been isolated from 18 different saline habitats, including inland salterns, marine salterns. 

On a relative basis, i.e. residues per 1000, there is virtually no one species like the other. In contrast, different shell samples from the same species and obtained from the same natural habitat yield identical amino acid patterns. It is of interest that (1) the structure of carbonates (aragonite-calcite-vaterite), (2) the content in trace elements, and (3) the stable isotope distribution are markedly effected by fluctuations in salinity, water temperature, Eh/pH conditions, and some anthropogenic factors. The same environmental parameters determine to a certain degree the chemical composition of the shell organic matrix. This feature suggests a cause-effect relationship between mineralogy and organic chemistry of a shell. In the final analysis, however, it is simply a reflection of the environmentally-controlled dynamics of the cell. 

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