Cell adaptations of Rhodococcus rhodochrous IEGM 66 to betulin biotransformation

Rhodococcus rhodochrous IEGM 1360, an Effective Biocatalyst of C3 Oxidative Transformation of Oleanane Triterpenoids

The optimal conditions for C3 oxidative biotransformation of 1.0 g/L pentacyclic triterpenoids oleanolic (OA) and glycyrrhetinic (GA) acids were determined using the resting cells of Rhodococcus rhodochrous IEGM 1360 from the Regional Specialised Collection of Alkanotrophic Microorganisms. Resting cell suspensions (OD₆₀₀ 2.6, pH 8.0, and OD₆₀₀ 2.2, pH 6.0) showed the highest catalytic activity against OA and GA, resulting in the formation of 61 and 100% of their 3-oxo derivatives, respectively. Using phase contrast, atomic force, and confocal laser scanning microscopy, an adaptive response of rhodococci to the effects of OA and GA was revealed. In silico, the apoptotic activity of 3-oxo-OA and antioxidant activity of 3-oxo-GA have been assumed. In vitro, a pronounced antibacterial activity of 3-oxo-OA against Micrococcus luteus, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis was shown. The absence of toxic effects of the above triterpenoids and their 3-oxo derivatives on aquatic objects and plants was demonstrated in silico and in vitro, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1134/S0026261722603360.

Adhesion of Rhodococcus bacteria to solid hydrocarbons and enhanced biodegradation of these compounds

Adhesive activities of hydrocarbon-oxidizing Rhodococcus bacteria towards solid hydrocarbons, effects of adhesion on biodegradation of these compounds by rhodococcal cells and adhesion mechanisms of Rhodococcus spp. were studied in this work. It was shown that efficiency of Rhodococcus cells' adhesion to solid n-alkanes and polycyclic aromatic hydrocarbons (PAHs) varied from 0.0 to 10.6·10⁶ CFU/cm². R. erythropolis IEGM 212 and R. opacus IEGM 262 demonstrated the highest (≥ 4.3·10⁶ CFU/cm²) adhesion. The percentage biodegradation of solid hydrocarbons (n-hexacosane and anthracene as model substrates) by Rhodococcus cells was 5 to 60% at a hydrocarbon concentration of 0.2% (w/w) after 9 days and strongly depended on cell adhesive activities towards these compounds (r ≥ 0.71, p < 0.05). No strict correlation between the adhesive activities of rhodococcal cells and physicochemical properties of bacteria and hydrocarbons was detected. Roughness of the cell surface was a definitive factor of Rhodococcus cell adhesion to solid hydrocarbons. Specific appendages with high adhesion force (≥ 0.6 nN) and elastic modulus (≥ 6 MPa) were found on the surface of Rhodococcus cells with high surface roughness. We hypothesized that these appendages participated in the adhesion process.

Biotransformation of (–)-Isopulegol by Rhodococcus rhodochrous

The ability of actinobacteria of the genus Rhodococcus to biotransform the monoterpenoid (–)-isopulegol has been established for the first time. R. rhodochrous strain IEGM 1362 was selected as a bacterium capable of metabolizing (–)-isopulegol to form new, previously unknown, 10-hydroxy (2) and 10-carboxy (3) derivatives, which may presumably have antitumor activity and act as respiratory stimulants and cancer prevention agents. In the experiments, optimal conditions were selected to provide the maximum target catalytic activity of rhodococci. Using up-to-date (TEM, AFM-CLSM, and EDX) and traditional (cell size, roughness, and zeta potential measurements) biophysical and microbiological methods, it was shown that (–)-isopulegol and halloysite nanotubes did not negatively affect the bacterial cells. The data obtained expand our knowledge of the biocatalytic potential of rhodococci and their possible involvement in the synthesis of pharmacologically active compounds from plant derivatives.

Response of Rhodococcus cerastii IEGM 1278 to toxic effects of ibuprofen

The article expands our knowledge on the variety of biodegraders of ibuprofen, one of the most frequently detected non-steroidal anti-inflammatory drugs in the environment. We studied the dynamics of ibuprofen decomposition and its relationship with the physiological status of bacteria and with additional carbon and energy sources. The involvement of cytoplasmic enzymes in ibuprofen biodegradation was confirmed. Within the tested actinobacteria, Rhodococcus cerastii IEGM 1278 was capable of complete oxidation of 100 μg/L and 100 mg/L of ibuprofen in 30 h and 144 h, respectively, in the presence of an alternative carbon source (n-hexadecane). Besides, the presence of ibuprofen induced a transition of rhodococci from single- to multicellular lifeforms, a shift to more negative zeta potential values, and a decrease in the membrane permeability. The initial steps of ibuprofen biotransformation by R. cerastii IEGM 1278 involved the formation of hydroxylated and decarboxylated derivatives with higher phytotoxicity than the parent compound (ibuprofen). The data obtained indicate potential threats of this pharmaceutical pollutant and its metabolites to biota and natural ecosystems.

Responses to Ecopollutants and Pathogenization Risks of Saprotrophic Rhodococcus Species

Under conditions of increasing environmental pollution, true saprophytes are capable of changing their survival strategies and demonstrating certain pathogenicity factors. Actinobacteria of the genus Rhodococcus, typical soil and aquatic biotope inhabitants, are characterized by high ecological plasticity and a wide range of oxidized organic substrates, including hydrocarbons and their derivatives. Their cell adaptations, such as the ability of adhering and colonizing surfaces, a complex life cycle, formation of resting cells and capsule-like structures, diauxotrophy, and a rigid cell wall, developed against the negative effects of anthropogenic pollutants are discussed and the risks of possible pathogenization of free-living saprotrophic Rhodococcus species are proposed. Due to universal adaptation features, Rhodococcus species are among the candidates, if further anthropogenic pressure increases, to move into the group of potentially pathogenic organisms with "unprofessional" parasitism, and to join an expanding list of infectious agents as facultative or occasional parasites.

Biotransformation of Oleanane and Ursane Triterpenic Acids

Oleanane and ursane pentacyclic triterpenoids are secondary metabolites of plants found in various climatic zones and regions. This group of compounds is highly attractive due to their diverse biological properties and possible use as intermediates in the synthesis of new pharmacologically promising substances. By now, their antiviral, anti-inflammatory, antimicrobial, antitumor, and other activities have been confirmed. In the last decade, methods of microbial synthesis of these compounds and their further biotransformation using microorganisms are gaining much popularity. The present review provides clear evidence that industrial microbiology can be a promising way to obtain valuable pharmacologically active compounds in environmentally friendly conditions without processing huge amounts of plant biomass and using hazardous and expensive chemicals. This review summarizes data on distribution, microbial synthesis, and biological activities of native oleanane and ursane triterpenoids. Much emphasis is put on the processes of microbial transformation of selected oleanane and ursane pentacyclic triterpenoids and on the bioactivity assessment of the obtained derivatives.

Bioconversion of ecotoxic dehydroabietic acid using Rhodococcus actinobacteria

Actinobactrial strains Rhodococcus erythropolis IEGM 267 and R. rhodochrous IEGM 107 were used to study biodegradation of dehydroabietic acid (DHA), a toxic tricyclic diterpenoid. The experiments were carried out in batch cultures of pre-grown rhodococci in the presence of 0.1% (v/v) n-hexadecane under aerobic conditions for 7 days. It was shown that R. erythropolis IEGM 267 and R. rhodochrous IEGM 107 partially and completely degraded DHA (500 mg/L), respectively. Characteristic physicochemical (reduced zeta potential) and morphological-physiological (increased average size of single cells and cell aggregates, increased root-mean-square roughness) changes in DHA-exposed actinobacteria were revealed. Products of DHA bioconversion by R. erythropolis IEGM 267 were analyzed and exhibited a previously unidentified metabolite 5α-hydroxy-abieta-8,11,13-triene-18-oat. The obtained experimental data widen the knowledge on the catalytic activity of rhodococci and their possible contribution to decontamination of natural ecosystems from pollutants.

Cell-Free Production of Pentacyclic Triterpenoid Compound Betulinic Acid from Betulin by the Engineered Saccharomyces cerevisiae

Betulinic acid is a product of plant secondary metabolism which has shown various bioactivities. Several CYP716A subfamily genes were recently characterized encoding multifunctional oxidases capable of C-28 oxidation. CYP716A12 was identified as betulin C-28 oxidase, capable of modifying betulin. This study aimed to induce the transformation of betulin to betulinic acid by co-expressing enzymes CYP716A12 from Medicago truncatula and ATR1 from Arabidopsis thaliana in Saccharomyces cerevisiae. The microsome protein extracted from the transgenic yeast successfully catalyzed the transformation of betulin to betulinic acid. We also characterized the optimization of cell fragmentation, protein extraction method, and the conversion conditions. Response surface methodology was implemented, and the optimal yield of betulinic acid reached 18.70%. After optimization, the yield and the conversion rate of betulin were increased by 83.97% and 136.39%, respectively. These results may present insights and strategies for the sustainable production of betulinic acid in multifarious transgenic microbes.