Amino acid composition of proteins in halophilic phototrophic bacteria of the genus Ectothiorhodospira

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Abstract
The amino acid composition of total proteins of 8 Ectothiorhodospira strains with different salt optima and of separated membranes of selected strains were determined. Amino acid compositions were compared with those reported for nonhalophilic phototrophic and heterotrophic bacteria and Halobacterium halobium. The membrane fractions from Ectothiorhodospira strains requiring high salt for maximum growth contained more polar and less nonpolar amino acids than strains with low salt requirements or nonhalophilic bacteria. The content of intermediate amino acids increased with the increasing halophilic properties of the Ectothiorhodospira strains. Proteins which function in high-salt environments may therefore require such compositions to maintain their structures in highly ionic solutions.