## 1 Introduction
Thus, the application of relatively low concentrations of PFD appears to be more attractive for enhancing the parameters of biotechnological processes involving recombinant cells. Despite the positive results that are achieved, addition of PFD to the culture growth media has not been used so far on the industrial scale, because the relatively high concentrations that are required, as well as the high cost of this substance makes this approach economically unviable for large-scale biotechnological processes. One of the ways to address this issue is multiple re-use of PFD in the biotechnological process, so that several production cycles can benefit from the use of the same portion of PFD, thus multiplying the target product output at lower cost. The possibility of separation of PFD from the culture medium upon completion of the processes via precipitation of this compound to the bottom of the reactor in case of periodical cultivation was previously shown [12]. However, this way of PFD separation works only for the processes where the target product of fermentation is an extracellular compound (e.g., antibiotic, hormone, secreted protein, etc.). In the cases when obtaining the intracellular target product (e.g., enzyme) involves biomass accumulation, followed by cell disintegration, the separation of cell precipitate from the layer of PFD actually is impossible by the regular way, and special procedures should be developed. Concurrently, an alternative approach to solving the problems of PFD application consists in looking for other PFCs with gas transfer function, which could affect the biotechnological processes in the same way as PFD does, but at much lower concentration of PFCs that are introduced into the cell culture medium. Carbogal and perfluoromethyldecalin are discussed as prospective substances for such studies [19], and perfluorohexane (PFH) also is noted [20]. However, only a few studies of the use of these compounds in processes involving recombinant _E. coli_ cells have been performed so far. Hexahistidine-containing organophosphorus hydrolase (His\({}_{6}\)-OPH) is one of the valuable intracellular enzymes produced using recombinant _E. coli_ cells (sequence of parent enzyme is available at UniProtKB P0A434). This enzyme can be applied for decomposing highly toxic organophosphorous substances previously produced as chemical weapon agents. Detoxification of such substances and of the products of their decomposition is essential for realizing the international programs on chemical disarmament [21]. Another important application for this enzyme is producing the unique and most modern antidotes that can be used against neurotoxic pesticides and chemical toxins [22]. Yet another application for this enzyme is developing new chemical agents with lactonase activity, which, being used in combination with antibiotics, can enhance the efficiency of the latter against antibiotic-resistant populations of gram-negative bacteria [23,24]. Thus, biotechnological studies that are aimed at enhancing the efficiency of His\({}_{6}\)-OPH synthesis are very topical. The purpose of this paper was studying the influence of various PFCs on the efficiency of biotechnological processes, as well as investigating the possibility of multiple reuse of PFCs in the process of recombinant _E. coli_ SG13009[pREP4] cell cultivation in order to produce the intracellular His\({}_{6}\)-OPH.