Influence of Low-Intensity Ultrasound on ε-Polylysine Production: Intracellular ATP and Key Biosynthesis Enzymes during Streptomyces albulus Fermentation

The effect of low-intensity sonication treatment on cell growth, ε-polylysine (ε-PL) yield and its biological mechanism were investigated, using a 3-L-jar fermenter coupled with an in situ ultrasonic slot with a Streptomyces albulus strain SAR 14-116. Under ultrasonic conditions (28 kHz, 0.37 W cm−2, 60 min), a high biomass of SAR 14-116 and concentration of ε-PL were realized (i.e., they increased by 14.92% and 28.45%, respectively) when compared with a control. Besides this, ultrasonication increased the mycelia viability and intracellular ATP as well as activities of key enzymes involved in the ε-PL biosynthesis pathway, resulting in an improvement in the production of ε-PL. Data on qRT-PCR revealed that ultrasonication also affected the gene expression of key enzymes in the ε-PL biosynthesis pathway, including ε-PL synthetase (PLS). These outcomes provided the basis for understanding the effects of ultrasound-assisted fermentation on the stimulation of metabolite production and fermentation procedure in a fermenter.