Ultrasound-enhanced Cell Production Of Lactic And Propionic Acid Bacteria Under Submerged Cultivation For Industrial Purposes
D. A. Durnikin, M. M. Silantyeva, O. V. Ereshchenko
Lactic and propionic bacteria are actively used as feed and food biopreservatives. The industrial production of these bacteria is carried out using known standard biotechnological approaches and equipment. However, the modern requirements to the volumes of their production require the development of new technologies providing the more intensive growth of bacterial biomass. One of the possible ways to do it is the use of nonspecific stimulators of chemical or physical origin. The stimulating effect of ultrasound on live systems attracts attention of many researchers. Depending on the sonication parameters and conditions, the impact of ultrasound on cell cultures can either stimulate or suppress their life processes. The possibility of the ultrasound stimulation of the biomass accumulation process has been studied for submerged bacterial cultures of Lactococcus lactis VPKM B-2092, Lactobacillus plantarum VPKM B-4173, and Propionibacterium acidipropionici VPKM B-2092. The inoculum with cell contentration of 1 · 108 mL-1 was sonicated at 880 kHz and energy density varied within 0.1-0.7 W/cm3 using a specially designed cuvette, through which the cell suspension was introduced into a fermenter at a rate of 10 mL/s that provided the total sonication time equal to 100-120 seconds. As a signal source, a standard therapeutical ultrasound apparatus UZT-1.01F equipped with a sweep generator was used. For all three cultures, the ultrasound stimulation resulted in a significant increase in the optical density of culture broth comparing to the control and the corresponding increase of the cell concentration. The optimum sonication energy density for the Lactococcus lactis VPKM B-2092, Lactobacillus plantarum VPKM B-4173, and Propionibacterium acidipropionici VPKM B-2092 was equal to 0.5, 0.3-0.5 и 0.3 W/cm3, respectively. Comparing to the control, the cell count of these strains in the culture broth increased in 28.6, 9, and 16.7 times, respectively. Thus, the ultrasound stimulation of inoculum provides a significant increase in the biomass of cells producing lactic and propionic acid that, in turn, increases the economic efficiency of their industrial use. Since the mechanisms of such stimulating action of ultrasound are well-studied, and the exploitation of ultrasound generators is simple and cheap, the further development of the ultrasound stimulation approach seems to be very promising for the industrial microbiology.