High Cell Density Fermentation Technology

High cell density fermentation by fed-batch strategies is one of the most cost-effective means of achieving high yields for the production of large scale recombinant proteins in the bio-industry. In fed-batch cultures, cell mass and productivity are maximized by adjusting culture conditions, including temperature and pH, the composition of the feed media, and the substrate feed rate. As one of the most critical factors to the success of high cell density culture, various nutrient feeding strategies have been developed.

High cell density VS Large scale（Picture from: Biologicscorp）

Feeding methods in fed-batch culture

Without feedback control

• Constant feeding - feeding nutrient at a predetermined (constant) rate. As a result, the specific growth ratecontinuously decreases.
• Increased feeding- feeding nutrient at an increasing (gradual, stepwise, or linear) rate. The decrease in specific growth rate can be compensated within a range.
• Exponential feeding- feeding nutrient at an exponential rate to achieve constant specific growth rate.

Notes:

Specific growth rate is maintained at a constant level by exponential feeding in most cases, but may deviate when unexpected conditions arise during culture. When it occurs, feedback control is required in the process to achieve constant specific growth rate.

With feedback control

Indirect feedback control

• DO-stat - feeding nutrient when there is a rise in the concentration of dissolved oxygen (DO), which results from depletion of the substrate.
• pH-stat - feeding nutrient when the pH rises after depletion of the principal carbon source.
• Carbon dioxide evolution rate (CER) - the most frequently method to maintain the specific growth rate. The CER is roughly proportional to the rate of consumption of the carbon source using a mass spectrometer.
• Cell concentration - the nutrient feeding rate determined from the cell concentration is measured by a laser turbidimeter.

Direct feedback control

• Substrate concentration control - nutrient feeding is directly controlled by the concentration of the principal carbon source (e.g. an on-line glucose analyzer in the fermentor).

From: Lee SY, High cell-density culture of Escherichia coli [J], Trends in Biotechnology, 1996 March: 14(3):98-105.

Fermentation Definiton

Industrial fermentation is the intentional use of fermentation by microorganisms such as bacteria and fungi to make products useful to humans. Fermented products have applications as food as well as in general industry. The rate depends on the concentration of microorganisms, cells, cellular components, and enzymes as well as temperature, pH and for aerobic fermentation oxygen. Product recovery frequently involves the concentration of the dilute solution. Nearly all commercially produced enzymes, such as lipase, invertase and rennet, are made by fermentation with genetically modified microbes. In some cases, production of biomass itself is the objective, as in the case of baker's yeast and lactic acid bacteria starter cultures for cheesemaking. In general, fermentations can be divided into four types:

1. Production of biomass (viable cellular material)

2. Production of extracellular metabolites (chemical compounds)

3. Production of intracellular components (enzymes and other proteins)

4. Transformation of substrate (in which the transformed substrate is itself the product)

These types are not necessarily disjoint from each other, but provide a framework for understanding the differences in approach. The organisms used may be bacteria, yeasts, molds, animal cells, or plant cells. Special considerations are required for the specific organisms used in the fermentation, such as the dissolved oxygen level, nutrient levels, and temperature.

Information from: wikipedia.org/wiki/Industrial_fermentation#Production_of_biomass