Blaga Angelova

Lipophilic compounds in biotechnology—interactions with cells and technological problems

Lipophilic compounds are of significant importance in modern biotechnology. Centerly of interest are the biodegradation as well as the biotransformation of such lipophilic and often water-immiscible substances. Both whole cells and/or enzymes are used for these processes. It is obvious that a wide range of problems arise in an application of such complex systems consisting of biocatalysts substrate(s), product(s), water, (in some cases water-immiscible organic solvents): (i) interactions between lipophilic compounds and the membranes resulting in the change of some physiological characteristics of the living system; (ii) problems in the transport of these compounds (substrates and/or products) within the complex structured reaction systems; (iii) the problem of increasing the solubility of the lipophilic and mostly water-immiscible compounds with a minimum of inhibition effects on the processes; (iv) the presence of lipophilic components may also cause changes of the transport processes within the system (e.g. immobilized cells) resulting in changed yield or activity of the biological system. These problems are critically discussed in this review in relation to the known modes of interaction of lipophilic compounds with membranes, the bioavailability of the substrates, and the cases of steroid biotransformations. An outlook of future aspects in research, development and application of such processes is given.

9α-Hydroxylation of 4-androstene-3,17-dione by resting Rhodococcus sp. cells

Abstract The effect of nitrogen and carbon nutrition, growth and biomass storage on the effectiveness of microbial 9α-hydroxylation of 4-androstene-3,17-dione was studied. The transformation was carried out by resting Rhodococcus sp. cells in nutrient deficient transformation medium at different pHs as well as in the presence of several solvents of the steroid compounds. A conversion ratio of ca 0·75 was observed with stationary phase cells grown on medium containing glucose and non-dehydrated casein hydrolysate. A strong influence of the nitrogen source on the effectiveness of the process was noticed. The presence of different alcohols in the reaction medium was found to increase the substrate conversion ratio to ca 0·85. A decrease in the transformation ability of stored cells was a logarithmic function of the storage time.

The inducibility of 9α-steroid hydroxylating activity in resting Rhodococcus sp. cells

Abstract The inducibility of the key enzyme systems controlling the microbial 9α-hydroxylation of 4-androstene-3,17-dione (AD) by resting Rhodococcus sp. IOC-77 cells was investigated. Consecutive induction of the 9α-steroid hydroxylating activity and the accompanying product degrading Δ 1 -steroid dehydrogenating activity of the organism was observed. The possibility of achieving a complete microbial conversion of AD into 9α-hydroxy-4-androstene-3,17-dione by blocking protein synthesis was demonstrated. The inducing properties of several androstane and pregnane compounds as well as the influence of some functional groups in their steroid structure were discussed.

Effect of Nitrogen Source in Cultivation Medium on the 9α-Hydroxylation of Pregnane Steroids by Resting Rhodococcus Sp. Cells

ABSTRACT The influence of the source of nitrogen in the cultivation media on 9α-hydroxylating activity of resting Rhodococcus sp. cells was investigated. Two pregnane steroids 3β-hydroxy-16α,17α-epoxy-5α-pregnane-20-one (5α-H) and 3β-hydroxy-16α,17α-epoxy-5- pregnen-20-one (Δ5) were used as substrates. Results obtained showed that the source of nitrogen in the cultivation medium significantly affected both the level of product accumulation and the dynamics of their formation. It is worth mentioning the difference in the hydroxylating activity of cell depot prepared on commercial dehydrated or freshly prepared nitrogen sources. Thus, the cultivation medium with Triptose (Difco) gave a Rhodococcus sp. cell depot actively accumulating hydroxylated derivatives from 5α-H while the most suitable for accumulation of such derivatives from Δ5 was media containing freshly prepared meat extract.

Bacterial Decolorization of Acid Orange 7 in the Presence of Ionic and Non-Ionic Surfactants

The effects of the non-ionic surfactant Triton® X-100, the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium N-lauroyl sarcosinate (SLS) on the decolorization of the reaction medium containing the monoazo dye Acid Orange 7 (AO7) by Alcaligenes faecalis and Rhodococcus erythropolis were studied. It was found that the surfactants influenced in different ways the rate of decolorization. At all concentrations tested the non-ionic surfactant Triton X-100 decreased the decolorization rate of R. erythropolis. At concentrations above the critical micelle concentration (CMC) Triton X-100 upset the usually observed exponential decay of the dye with A. faecalis due probably to the existence of an outer membrane in this organism. In concentrations above the CMC the anionic surfactant SLS inhibited the decolorization and, at prolonged incubation, caused partial release of the bound dye. The cationic surfactant CTAB in concentrations above and below the CMC accelerated drastically the binding of AO7 to the cells causing a rapid staining of the biomass and complete decolorization of the reaction medium. An attempt was made for explanation of the observed differences by the negative electrostatic charge of the living bacterial cell.