We compared amino acid solvent accessibilities and helix propensities in data sets of Escherichia coli and Bacillus subtilis proteins. These species reside in very different environments and hold very different physiological properties. From the observations, it was proposed that the cytoplasm of B. subtilis is more ion-rich compared to the cytoplasm of E. coli, which might be more hydrophobic; therefore, during evolution these differences have resulted in different protein folding tracks. Such inherent differences imply that the results of bioinformatic analyses of protein structures might depend on the species from which the proteins are picked. It is also suggested that different cytoplasmic environments cause E. coli and B. subtilis to be appropriate for expression of distinct types of proteins.