It's definitely the exception to the rule for university-based research facilities to conduct cell-culture studies utilizing
the capabilities of a fermentor. Recently BioPharm International capitalized on an opportunity to chat with noted cell culture researcher Scott Stevens, who currently is growing a diverse
group of cultures with the use of a fermentor at his facility at the University of Texas at Austin, with noteworthy results.
Fermentation Facility at University of Texas at Austin
Describe the work you're doing in the laboratory at University of Texas at Austin and what you hope to accomplish.
Stevens: In my laboratory we study ribonucleoprotein structure and function, specifically the structure and function of those ribonucleoproteins
involved in gene expression. The small nuclear ribonucleoproteins (snRNPs), which are our primary interest, are present in
relatively low abundance (200 to 500 molecules per cell in yeast) making their isolation and structural characterization a
particular challenge. We hope to determine the low-resolution structural arrangement of these snRNPs by cryoelectron microscopy
and eventually, the high-resolution structure by X-ray crystallography. To produce milligram-scale quantities of these complex
molecules that contain dozens of proteins and several small RNA molecules, we require multiple kilograms of yeast. The strains
we use for these experiments contain specific modifications in several genes to facilitate the snRNP purifications, so we
are unable to use commercially available wild-type yeast cakes.
What cultures do you grow in the laboratory?
Stevens: We primarily grow Saccharomyces cerevisiae in our laboratory, but we also grow Schizosaccharomyces pombe and Escherichia coli.
For what purpose(s) do you grow the cultures?
Stevens: For our large-scale microorganism growth, we generally use the product for protein or macromolecular complex purification.
For S. cerevisiae and E. coli we perform preparative purifications of single polypeptides (E. coli), or multi-protein complexes (S. cerevisiae). For S. pombe we perform exploratory analyses of macromolecular complex composition.
Describe the processes and technology you originally employed to grow cultures and the progression to those you use today?
Stevens: Like most academic investigators performing similar experiments, we began experimentation using small-scale cultures of one
to six liters in shake-flasks. We continue to perform small-scale experiments to troubleshoot and optimize our purification
procedures. We now are able to routinely produce 400 liters of culture in a fermentor (500L Modular BioFlo Pro,New Brunswick
Scientific [NBS]) in an overnight experiment. We find that although using the fermentor typically allows for faster and more
dense culture growth, the procedures scale directly and the resulting product is identical to what is produced from smaller-scale
cultures. We are currently attempting to optimize culture conditions with oxygen supplementation to increase the biomass
yield at the end of the culture growth. With the equipment we use, there have been no challenges to overcome in scaling to
this level, other than learning how to operate the equipment.
How customary is it for a college or university laboratory to use a fermentor to grow culture?
Stevens: In researching the purchase of the equipment for our facility, we found that many academic laboratories, departments, and
colleges that used large-scale fermentation at one time have discontinued their use in the last several years. In the past
decade or more, laboratories interested in milligram quantities of protein have dispensed with large-scale growth of microorganisms
as bacterial over-expression systems have progressed to the point where hundreds of milligrams of product can often be purified
from one to five liters of culture. In the current age of structural genomics where the low-hanging fruit of easily expressed
single polypeptides will have their structures determined rapidly, these small-scale culture are ideal.