## 1 Introduction  
Many modern biotechnological processes use recombinant cells as producers of different target products, and bacteria _Escherichia coli_ are microorganisms that are most widely used for producing genetically modified proteins [1; 2]. This is due to the wealth of knowledge on this species, high cell growth rate, the accessibility of modern techniques for genetic manipulation, and great progress in realization of biotechnological processes. In particular, _E. coli_ cells are used for producing therapeutic proteins and industrial enzymes (restriction enzymes, DNA polymerase, enterokinase, L-asparaginase, streptokinase, ligases, amylases, invertase, cellulases, xylanase, etc. ), antibodies, growth factors, interferons, insulin) [3; 4; 5; 6; 7]. In order to optimize such processes, the biotechnologists usually aim at maximizing such process characteristics as the growth rate of the bacterial cells, the rate of biomass increase, and that of target substance accumulation in the bacterial cells. This approach allows for reducing the costs, first of all in terms of energy consumption. The efficiency of the biotechnological processes involving high concentrations of aerobic producing cells is often limited by the intensity of mass exchanged processes, in particular, that of mass transfer of air in the medium [8]. In most cases, the mass exchange is enhanced via increasing the rate of air flow into the reactor, or the intensity of mechanical or bubble mixing. However, this increases the turbulence of the liquid flow in the reactor and causes negative respond of cultivated cells as result of their shear deformation or stress [9]. Application of perfluorocarbon compounds (PFCs) as oxygen carriers is considered as one of the prospective approaches to increasing the efficiency of the biotechnological processes with different types of microorganisms. PFCs are derivatives of aliphatic, cyclic, or polycyclic hydrocarbons, where most of the hydrogen atoms (or even all of them) are substituted with fluorine [10]. The basic feature of PFCs, which ensures their efficient use in biotechnology, is the solubility of oxygen in such substances (up to 20 times that in water). Besides, PFCs are highly neutral (both chemically and biologically), stable, and have low toxicity towards biological systems. Most of such substances, depending on their boiling temperature, can be sterilized via autoclaving [11]. Being hydrophobic, most PFCs can be easily separated from the water phase, and can be re-used (upon regeneration, when necessary) in the biotechnological processes [12]. It is known that the introduction of perfluorodecalin (PFD) into the media for cultivation of microorganisms allows for increasing the amount of accumulated biomass and to reduce the required cultivation time [13]. Many researchers have shown that the use of PFD as an additive in cultivation of recombinant bacterial strains can help increasing both the biomass output and, in certain cases, the level of recombinant protein expression [14; 15]. However, PFD is currently almost the only substance among the many known PFCs, which is actively used in such studies [16]. Note that to achieve the necessary results, rather large quantities of PFD have to be introduced into the medium (5-50 vol. %) [14]. Thus, the introduction of PFD at 50 vol. % produces a 40% increase in the biomass output of genetically modified _E.coli_ RB791 pAdh cells, which synthesizes the recombinant alcohol dehydrogenase [17]. In another case, a 20% increase in amount of accumulated biomass for genetically modified _E. coli_ RB791 pQE30 adh cells was observed when 50 vol. % of PFD was added to the culture medium [15; 18]. Note that lower concentrations of PFD in some cases proved more effective. In particular, addition of 0.5-12.5 vol. % of PFD to the medium caused an increase in cell suspension density by a factor of up to 3, and the transition from the exponential to the stationary phase of growth for the _E. coli_ M-17 strain was observed 1 h earlier than in the control sample without PFD [13].