Abstract: The physiological responses of the ε-poly-l-lysine-producing strain Streptomyces diastatochromogenes T17 and its acid-resistant derivatives, S. diastatochromogenes AE44, S. diastatochromogenes AE51 and S. diastatochromogenes AE56, to spontaneous acid stress were investigated. The changes in relevant physiological indexes of the original and evolutionary strains were compared at two stages of acidic stress. The results showed that at 0 h (pH 6.5), there were no significant differences in the physiological indexes between the original and evolutionary strains. At 48 h (pH 3.2), compared to the original strain, the intracellular pH, ATP concentration and H+-ATPase activity of the evolutionary strains were significantly increased, accompanied by increased levels of intracellular aspartic acid, alanine, glutamic acid, lysine, glycine and proline. The ratio of unsaturated to saturated fatty acids (U/S ratio) in the cell membrane was also increased so that the membrane fluidity was improved. Collectively, we conclude that the evolutionary strains could achieve a balance during spontaneous acid stress.

Key words: ε-poly-l-lysine, Streptomyces diastatochromogenes T17, acidic adaptive evolution, spontaneous acid stress, physiological mechanism of acid resistance