## 3 Results  
### Cultivation of Recombinant Protein-Producing Cells in Media Containing PFCs  
Perfluorohexane (PFH), perfluorodecalin (PFD), and perfluoroaliphatic ethers I and II, with different characteristics as gas-transfer substances, were used in this study (Table 1). Their choice was based on the physico-chemical properties of these compounds, which differ essentially from those of other substances of the same type. The physical properties of these compounds determine the conditions of their application in biotechnological processes and the possible ways of their recycling for multiple use, and also, most probably, the degree of their influence on the parameters of the biotechnological process. PFH had the lowest boiling temperature and molecular mass, and had the highest solubility in water [11; 13; 17; 30; 31]. Analysis of the influence of these substances on the growth of _E. coli_ SG13009[pREP4] cells that were transformed with pTES-His\({}_{6}\)-OPH plasmid and on the synthesis of the His\({}_{6}\)-OPH was performed via varying the initial concentrations of these PFCs in the initial culture medium in the range of 0.3%-5% (\(v/v\)) (Figure 1a,b, Table 2). Cultivating of the same cell strain under identical conditions, but in the absence of PFCs was used for control. The obtained results showed that the introduction of any of the studied gas transfer-capable substances with concentration up to 3% (\(v/v\)) leads to an increase of the biomass of the cells (Figure 1a) producing His\({}_{6}\)-OPH, and also, in some cases, to an increase of the His\({}_{6}\)-OPH activity of the cells per 1 g of dry biomass (Figure 1b). The studies have shown that introduction of PFD into the medium for cultivating _E. coli_ SG13009[pREP4] cells transformed with pTES-His\({}_{6}\)-OPH plasmid leads to a very slight increase in the accumulated biomass (by \(\sim\)1%-2%) of the total output, and the specific His\({}_{6}\)-OPH activity was 3% greater (Figure 1a,b). Addition of 0.5% (\(v/v\))of PFH to the culture liquid caused the maximum His\({}_{6}\)-OPH-activity of the cells when compared to the cases of all the other PFCs (and their concentrations) studied, whereas the level of biomass accumulation in the medium was close to the average one (Figure 1a). It was also established that increasing the concentration of this substance beyond 1% (\(v/v\)) caused a decrease of the specific His\({}_{6}\)-OPH-activity of the cells (Figure 1b). The specific cell growth rate for _E. coli_ SG13009[pREP4] upon the addition of gas transfer-capable substances to the culture medium was almost the same as in the absence of such substances (Table 2). However, after 24 h of cultivating cells in the absence of PFCs, the stationary growth phase was reached, whereas in the presence of PFCs, the growth after 24 h still demonstrated logarithmic manner, so that the total biomass output that is presented in Figure 1a was greater in the latter case. Upon addition of polyether I to the culture medium no essential dependence of the accumulated recombinant cell biomass on the concentration of the additive was established. The total increase of cell biomass with this additive was 11%-19% when compared to control. Addition of polyether II caused the maximum biomass concentration increase in the culture medium (by 37%) among all the PFCs (and their concentrations) studied. In terms of His\({}_{6}\)-OPH-activity of the cells the optimum concentration of polyether I was 0.5% (\(v/v\)), and that of polyether II was 1% (\(v/v\)). Analysis of the evaluated total enzymatic activity accumulated in the cells (Table 3) has shown that the maximum efficiency can be achieved for PFH and polyether concentration in the culture medium within the range of 0.5%-1% (\(v/v\)). Increasing the concentration of PFCs beyond 1% (\(v/v\)) was inefficient, because there was no further increase in biomass accumulation or the specific activity of the cells to show for the additional PFC that was spent.