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.

No abstract

Using the bioresources of the Regional Specialised Collection of Alkanotrophic Microorganisms (acronym IEGM, Perm, Russia; WFCC # 285), R. rhodochrous IEGM 757 was selected, which catalyzed the C5, C22, and C23 functionalization of pentacyclic triterpenoid oleanolic acid (OA, 3β-hydroxyolean-12-en-28-oic acid, 1.0 g/L) to form a new 5α,22α-dihydroxy derivative of gypsogenic acid (3β,5α,22α-trihydroxyolean-12-ene-23,28-dioic acid) for 5 days. In silico analysis showed that, compared to the native triterpenoid, the OA metabolite may be more soluble in water and less ecotoxic, act as an apoptosis agonist and insulin promoter, and have chemopreventive and analgesic effects. Phase-contrast, fluorescent, scanning, and transmission electron microscopy and X-ray spectroscopy demonstrated the high resistance of R. rhodochrous IEGM 757 to OA. This creates opportunities for further research and development of a method for the production of the OA metabolite. New-generation sequencing of the R. rhodochrous IEGM 757 whole genome, annotation and bioinformatics analysis of the obtained sequences, and real-time PCR were applied. As a result, 24 genes encoding CYP450 enzymes were found, which are highly likely to be involved in the process of OA oxidation.

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.

Drugs derived from secondary plant metabolites make up about 25% of the global pharmaceutical market [1]. Oleanane pentacyclic triterpenoids, in particular oleanolic (OA) and glycyrrhetinic (GA) acids, are the most of interest for researchers in medical chemistry and used to obtain derivatives with pronounced antiviral, antimicrobial, anti-inflammatory, antitumor, and hepatoprotective activities. Along with chemical synthesis, biological methods of OA and GA transformations have been actively developing, which allow to obtain valuable derivatives without the use of aggressive reagents and can be carried out under normal temperature, pressure and pH values. Furthermore, microbial conversion ensures selective modifications of triterpenic molecule sites that are either not modified or poorly modified by chemical transformations [2]. Among the known microbial biocatalysts, members of mycelial fungi are the most studied, but their use on a preparative scale is technologically impossible and dangerous due to the mycelial type of their growth and the ability to produce mycotoxins with pronounced mutagenic and carcinogenic effects. Whereas bacterial catalysts are only represented by a few species of Bacillus, Nocardia and Streptomyces genera, including pathogens, exhibiting catalytic activity at a concentration of OA and GA no more than 0.3 g/L [3]. In this context, it is essential to search for new non-pathogenic bacterial strains able to carry out site-directed transformations of OA and GA. One of the intensively studied groups of microorganisms in terms of biotechnological application is non-pathogenic actinobacteria. Nonmycelial growth, synthesis of biosurfactants, the ability to grow on minimal media, a flexible metabolic system and high oxygenase activity determine the prospects for actinobacteria to be used as perspective biocatalysts for biotransformation of OA and GA [4]. Moreover, the ability of actinobacteria of genus Rhodococcus to transform pentacyclic triterpenoid betulin with formation of betulone was previously shown [5]. In this work, 76 strains of actinobacteria from the Regional Specialized Collection of Alkanotrophic Microorganisms (official acronym IEGM; the World Federation of Culture Collections number 285; the Unique Research Facility number 73559; www.iegmcol.ru) belonging to the species Corynebacterium ammoniagenes (1), C. glutamicum (1), Gordonia terrae (4), R. aetherivorans (1), R. cercidiphylli (1), R. erythropolis (14), R. fascians (2), R. jostii (3), R. opacus (15), R. qingshengii (2), R. rhodochrous (6) and R. ruber (26) were used. OA (≥98%, Acros Organics, USA) and GA (≥98%, Shanghai Yuanye Bio-Technology Co, China), dissolved in dimethyl sulfoxide (1:10 mg/μL), were used at a concentration of 1.0 g/L.Bacterial cells were visualized and their morphometric parameters were measured using an Axio Imager M2 microscope (Zeiss, Germany) equipped with an Axiocam 506 Color camera (Zeiss, Germany) in phase contrast mode with a magnification of x1000. To determine the localization of enzymes, crude...

Organic wood extractives—resin acids—significantly contribute to an increase in the toxicity level of pulp and paper industry effluents. Entering open ecosystems, resin acids accumulate and have toxic effects on living organisms, which can lead to the ecological imbalance. Among the most effective methods applied to neutralize these ecotoxicants is enzymatic detoxification using microorganisms. A fundamental interest in the in-depth study of the oxidation mechanisms of resin acids and the search for their key biodegraders is increasing every year. Compounds from this group receive attention because of the need to develop highly effective procedures of resin acid removal from pulp and paper effluents and also the possibility to obtain their derivatives with pronounced pharmacological effects. Over the past fifteen years, this is the first report analyzing the data on distribution, the impacts on living organisms, and the microbial transformation of resin acids. Using the example of dehydroabietic acid—the dominant compound of resin acids in effluents—the review discusses the features of interactions between microorganisms and this pollutant and also highlights the pathways and main products of resin acid bioconversion.

The ability of actinobacteria of the genus Rhodococcus to transform oleanolic acid (OA), a plant pentacyclic triterpenoid, was shown for the first time using bioresources of the Regional Specialized Collection of AlkanotrophicMicroorganisms (IEGM; WDCM #768;www.iegmcol.ru). The most promising strains (R.opacus IEGM 488 and R.rhodochrousIEGM 285) were selected, and these catalyzed80% bioconversion of OA (0.5 g/L) in the presence of n-hexadecane (0.1% v/v) for seven days. The process of OA bioconversion was accompanied by a gradual decrease in the culture medium pH. Adaptive responses of bacterial cells to the OA effects included the formation of compact cellular aggregates, a marked change in the surface-to-volume ratio of cells, and a significant increase in the Zeta potential values. The results demonstrated that the process of OA bioconversion was catalyzed by membrane-bound enzyme complexes. Participation of cytochrome P450-dependent monooxygenases in the oxidation of the OA moleculewas confirmedusing specific inhibitors. The obtained data expand our knowledge on the catalytic activity of actinobacteria of the genus Rhodococcus and their possible use as biocatalysts for the bioconversion of complex hydrophobic compounds. The results can also be used inthe searchfor promising OA derivatives to be used in the synthesis of biologically active agents. Keywords: bioconversion, oleanolic acid, Rhodococcus, biologically active compounds

Terpenes and their derivatives (terpenoids and meroterpenoids, in particular) constitute the largest class of natural compounds, which have valuable biological activities and are promising therapeutic agents. The present review assesses the biosynthetic capabilities of actinomycetes to produce various terpene derivatives; reports the main methodological approaches to searching for new terpenes and their derivatives; identifies the most active terpene producers among actinomycetes; and describes the chemical diversity and biological properties of the obtained compounds. Among terpene derivatives isolated from actinomycetes, compounds with pronounced antifungal, antiviral, antitumor, anti-inflammatory, and other effects were determined. Actinomycete-produced terpenoids and meroterpenoids with high antimicrobial activity are of interest as a source of novel antibiotics effective against drug-resistant pathogenic bacteria. Most of the discovered terpene derivatives are produced by the genus Streptomyces; however, recent publications have reported terpene biosynthesis by members of the genera Actinomadura, Allokutzneria, Amycolatopsis, Kitasatosporia, Micromonospora, Nocardiopsis, Salinispora, Verrucosispora, etc. It should be noted that the use of genetically modified actinomycetes is an effective tool for studying and regulating terpenes, as well as increasing productivity of terpene biosynthesis in comparison with native producers. The review includes research articles on terpene biosynthesis by Actinomycetes between 2000 and 2022, and a patent analysis in this area shows current trends and actual research directions in this field.