Abstract
We have investigated the growth kinetics of heterotrophic Chlorellavulgarisusing a droplet based PDMS microfluidic chip. Traditionally the growth kinetics are investigated by measuring the optical density, biomass or the cell number of representative samples of the cell culture over time. In this study, we investigated the growth kinetics by observing the total number of cells. The kinetic parameters are determined by counting the total number of cells under investigation during the entire period of the experiment. The PDMS chip was designed with an array of fluidic network containing a repeated sequence of loops. Each loop consists of two branches with the lower branch containing a droplet trap. The droplets were created using hydrostatic pressure. The droplets were created inside mineral oil. The sizes of the droplets were ranged from 10 to 12 nL. For long term storage of the droplets, the chip was needed to be stored with water underneath. The growth medium for the algae was made of proteose, glucose, and minerals. In order to count the cells, images of the droplets were taken once every day using a bright field microscope. Figure 1 shows example growth curves of algae in four different droplets. The inset table shows the initial cell number (No), the final cell number (Nt), the average cell division rate (ᵟ), and the maximum specific growth rate (µ) based on cell numbers in the exponential phases. We found that kinetic parameters are different even if the initial cell numbers are the same. We hypothesize that it is because the growth kinetics of Chlorellavulgarisdepend on the initial cell conditions such as the age of the algae culture, and the size distribution.
Numberofcellsinadroplet
32028024020016012080400
0481216 Time(days) Figure 1. Growth kinetics of Chlorellavulgarisinside dropletarrays
of PDMS microfluidic chip.
