Genetically Engineered Cell Culture Fermentation

One of the major breakthroughs of exploitation of genetically engineered cell culture fermentation is the development of a stable redesigned cell using recombinant plasmid vector for production of a metabolite in large scale fermenter.

It involves keeping plasmid barriers most favourable in cell population when recombinant plasmid technique is used in fermentation industry.

A typical series step that has been followed in scale up of such host-vector fermentation process is as below.

(a) Transfer of cells ascetically from slant to conical flask in 20 ml of liquid medium.

(b) Transfer of inoculum from (a) in medium of larger conical flask (250-300 ml).

(c) Asceptic transfer of inoculum from (b) into the medium of a jar fermenter (101).

(d) The seed culture from (c) is transferred to a pilot scale fermenter (3000 1).

(e) Finally, from the seed culture vessel in (d) the transfer was made ascetically into the production scale fermenter (100,000 I) medium.

Considering inoculum size in each step is 3% v/v, the number of cell generations (n) needed from step to step may be computed to be 5 and supposing that cells to be harvested in each culture be around 1.0 ( = 0.03 x 2⁵) the total number of n required for scale up would be

In case of rDNA (recombinant DNA) fermenter scale up with physical containment requirement, however, the pilot plant is generally considered to be large scale (greater than 101). The host- vector system to be used mainly determines the level of physical containment required. As per NIH guidelines of 1978 for recombinant DNA research, genetically engineered cell fermentation scale up is restricted to 10 L or less in P-3 level containment conditions.

Scale Down:

By scale down it is meant in bioprocessing that a microbial production rate of a specific metabolite in a full scale plant is reproduced by some means to pilot plant vessels (i.e. transfer from production scale to pilot scale maintaining some criteria constant). Identities in both systems/scales with respect to time dependence of sugar consumption rate, pH, dissolved oxygen concentration etc. must be underlying the identity of product accumulation pattern.

Criteria:

Referring to the criteria on scale up one may choose again either one of the following as constant:

(i) Power input per unit volume of liquid

(ii) Shear rate of impeller

(iii) Volumetric oxygen transfer coefficient

(iv) Momentum transfer etc. in scale down.

However, a proper selection cannot be made a priori, because a direct correlation between microbial activity and environmental conditions, which are represented by the above scale up (and/or scale down) criteria still seems prohibitive.