Agitation of Microbial Cultures Via Low-Frequency Acoustic Energy for Improved Oxygen Transfer

Conventional biological orbital shakers have substantial drawbacks that include low volumetric capacities, limited oxygen transfer capability and difficulty in mixing viscous liquid cultures. A novel mixing technology has been developed to overcome these limitations by applying low-frequency, high intensity acoustic energy to agitate liquid cultures. This new technology has been incorporated into a new incubator system offered by Applikon Biotechnology. This advanced technology is a significant improvement over orbital shaker/incubator devices, as it has been shown to dramatically enhance oxygen transfer, as well as substantially improve bulk mixing for microbial cultures. Combined with the novel air-pumping (Oxy-PumpTM, Applikon Biotechnology, Inc.) stopper, oxygen transfer rates up to 6-fold higher than orbital-shaken cultures can be achieved using the technology. Studies comparing the oxygen mass transfer coefficients between this technology and conventional orbital shaker technology will be presented. Various factors that influence the degree of oxygen transfer, including stopper design, intensity of agitation, vessel geometry, volumetric loading, and antifoam inclusion will be discussed. Culture experiments utilizing an E. coli HB101 strain engineered to express Green Fluorescent Protein (GFP) were used to compare orbital shakers (400rpm) to the acoustic mixing technology and peak biomass levels and GFP expression levels were found to be 4-fold and 14-fold higher, respectively, using the acoustic mixing technology. Additional studies using Pseudomonas fluorescens, Bacillus subtilis, Aspergillus oryzae, and Penicillium raistrickii have all shown enhanced biomass levels using the acoustic mixing system. This new technology has substantial potential to enhance the productivity of a wide range of microbial culture systems.&'