Dynamic Responses of Streptomyces albulus QLU58 and Its Acid-Tolerant Derivatives to the Autoacidification in e-Poly-l-Lysine Production

Streptomyces albulus is a kind of safety bacteria that is used to produce a natural food preservative named e-poly-l-lysine (e-PL). Environmental autoacidification (the pH declined from 6.8 to approximately 3.0) inevitably occurred in e-PL biosynthesis by S. albulus. In this study, the dynamic responses of S. albulus QLU58 and its acid-tolerant mutants to autoacidification were investigated at the physiological and transcriptional levels. The results showed that cell growth, e-PL production, cell respiratory activity, and intracellular pH (pH(i)) homeostasis were disturbed by autoacidification. In the initial autoacidification stage (before 24 h), the acid tolerance of S. albulus was effectively improved by increasing the intracellular ATP and related amino acids contents and the H+-ATPase activity, regulating the membrane fatty acids composition, and maintaining the pH(i) at about 7.7. However, as the autoacidification degree deepened (after 24 h), the metabolic activities decreased and negative cell growth appeared, which weakened the acid tolerance and caused the pH(i) to decline to about 6.5. Additionally, the acid-tolerant mutants exhibited better performances during autoacidification, which was also confirmed by the related genes' improved transcription levels. These results provide references for the analysis of progressive environmental modification in e-PL production.

Automated summary

In this study, the dynamic responses of Streptomyces albulus QLU58 and its acid-tolerant mutants to autoacidification were investigated at the physiological and transcriptional levels. The results showed that autoacidification disturbed cell growth, e-PL production, cell respiratory activity, and intracellular pH (pH(i)) homeostasis. Acid-tolerant mutants exhibited better performances during autoacidification, which was also confirmed by the improved transcription levels of related genes.