Single-cell protein continuous culture

Because of the need to avoid mutations and maintain the superior qualities of the genetically developed strain, batch or fed-batch operations are used in most applications. Continuous culture operations, however, provide a time-invariant environment that facilitates greatly the study of a biological process in research laboratories. Moreover, some industrial operations employ continuous reactors, such as the single-cell protein facility of ICI in Billingham, England (total reactor volume of about 2,300 m3), all waste treatment processes, and others. It should be noted that it is relatively common to follow a batch process with a period of fed-batch or continuous operation. Also, in most cases batch cultivation is the optimal start-up procedure for continuous or fed-batch cultivation (Yamane et al, 1977). 

Figure 3. Strategies for optimization of continuous culture for production of single-cell protein. Top, under continuous culture isotherm with a fixed value for carbon source feed concentration. D is the dilution rate of maximum productivity. Bottom, comparison of isotherm for fixed substrate feed concentration. So, with that for fixed oxygen transfer rate, OTR (curves show the maximum cell concentration for a given OTR and cell yield).

Two studies have used pseudotyped vesicular stomatitis virus (VSV) and rabies virus with CD4 and CXCR4 in place of their normal envelope proteins (Mebatsion et al., 1997 Schnell et al., 1997). This system targets a cytolytic virus to HIV-infected cells. While the rabies-virus pseudotype was only able to undergo a single round of infection, the VSV pseudotype could continue to propagate in culture, destroying HIV-infected cells. 

---