Investigations on the Degradation of the Bile Salt Cholate via the 9,10-Seco-Pathway Reveals the Formation of a Novel Recalcitrant Steroid Compound by a Side Reaction in Sphingobium sp. Strain Chol11

Bile salts such as cholate are steroid compounds from the digestive tracts of vertebrates, which enter the environment upon excretion, e.g., in manure. Environmental bacteria degrade bile salts aerobically via two pathway variants involving intermediates with Δ1,4- or Δ4,6-3-keto-structures of the steroid skeleton. Recent studies indicated that degradation of bile salts via Δ4,6-3-keto intermediates in Sphingobium sp. strain Chol11 proceeds via 9,10-seco cleavage of the steroid skeleton. For further elucidation, the presumptive product of this cleavage, 3,12β-dihydroxy-9,10-seco-androsta-1,3,5(10),6-tetraene-9,17-dione (DHSATD), was provided to strain Chol11 in a co-culture approach with Pseudomonas stutzeri Chol1 and as purified substrate. Strain Chol11 converted DHSATD to the so far unknown compound 4-methyl-3-deoxy-1,9,12-trihydroxyestra-1,3,5(10)7-tetraene-6,17-dione (MDTETD), presumably in a side reaction involving an unusual ring closure. MDTETD was neither degraded by strains Chol1 and Chol11 nor in enrichment cultures. Functional transcriptome profiling of zebrafish embryos after exposure to MDTETD identified a significant overrepresentation of genes linked to hormone responses. In both pathway variants, steroid degradation intermediates transiently accumulate in supernatants of laboratory cultures. Soil slurry experiments indicated that bacteria using both pathway variants were active and also released their respective intermediates into the environment. This instance could enable the formation of recalcitrant steroid metabolites by interspecies cross-feeding in agricultural soils.

Degradation of Bile Acids by Soil and Water Bacteria

Bile acids are surface-active steroid compounds with a C5 carboxylic side chain at the steroid nucleus. They are produced by vertebrates, mainly functioning as emulsifiers for lipophilic nutrients, as signaling compounds, and as an antimicrobial barrier in the duodenum. Upon excretion into soil and water, bile acids serve as carbon- and energy-rich growth substrates for diverse heterotrophic bacteria. Metabolic pathways for the degradation of bile acids are predominantly studied in individual strains of the genera Pseudomonas, Comamonas, Sphingobium, Azoarcus, and Rhodococcus. Bile acid degradation is initiated by oxidative reactions of the steroid skeleton at ring A and degradation of the carboxylic side chain before the steroid nucleus is broken down into central metabolic intermediates for biomass and energy production. This review summarizes the current biochemical and genetic knowledge on aerobic and anaerobic degradation of bile acids by soil and water bacteria. In addition, ecological and applied aspects are addressed, including resistance mechanisms against the toxic effects of bile acids.

Proteome, bioinformatic and functional analyses reveal a distinct and conserved metabolic pathway for bile salt degradation in the Sphingomonadaceae

Bile salts are amphiphilic steroids chain with digestive functions in vertebrates. Upon excretion, bile salts are degraded by environmental bacteria. Degradation of the bile-salt steroid skeleton resembles the well-studied pathway for other steroids like testosterone, while specific differences occur during side-chain degradation and the initiating transformations of the steroid skeleton. Of the latter, two variants via either Δ 1,4 - or Δ 4,6 -3-ketostructures of the steroid skeleton exist for 7-hydroxy bile salts. While the Δ 1,4 - variant is well-known from many model organisms, the Δ 4,6 -variant involving a 7-hydroxysteroid dehydratase as key enzyme has not been systematically studied. Here, combined proteomic, bioinformatic and functional analyses of the Δ 4,6 -variant in Sphingobium sp. strain Chol11 were performed. They revealed a degradation of the steroid rings similar to the Δ 1,4 -variant except for the elimination of the 7-OH as a key difference. In contrast, differential production of the respective proteins revealed a putative gene cluster degradation of the C 5 carboxylic side chain encoding a CoA-ligase, an acyl-CoA dehydrogenase, a Rieske monooxygenase, and an amidase, but lacking most canonical genes known from other steroid-degrading bacteria. Bioinformatic analyses predicted the Δ 4,6 -variant to be widespread among the Sphingomonadaceae , which was verified for three type strains which also have the predicted side-chain degradation cluster. A second amidase in the side-chain degradation gene cluster of strain Chol11 was shown to cleave conjugated bile salts while having low similarity to known bile-salt hydrolases. This study signifies members of the Sphingomonadaceae remarkably well-adapted to the utilization of bile salts via a partially distinct metabolic pathway. Importance This study highlights the biochemical diversity of bacterial degradation of steroid compounds, in particular bile salts. Furthermore, it substantiates and advances knowledge of a variant pathway for degradation of steroids by sphingomonads, a group of environmental bacteria that are well-known for their broad metabolic capabilities. Biodegradation of bile salts is a critical process due to the high input of these compounds from manure into agricultural soils and wastewater treatment plants. In addition, these results may also be relevant for the biotechnological production of bile salts or other steroid compounds with pharmaceutical functions.

Proteome, bioinformatic and functional analyses reveal a distinct and conserved metabolic pathway for bile salt degradation in the Sphingomonadaceae

Bile salts are amphiphilic steroids with a C5 carboxylic side chain with digestive functions in vertebrates. Upon excretion, they are degraded by environmental bacteria. Degradation of the bile-salt steroid skeleton resembles the well-studied pathway for other steroids like testosterone, while specific differences occur during side-chain degradation and the initiating transformations of the steroid skeleton. Of the latter, two variants via either Δ1,4- or Δ4,6-3-ketostructures of the steroid skeleton exist for 7-hydroxy bile salts. While the Δ1,4- variant is well-known from many model organisms, the Δ4,6-variant involving a 7-hydroxysteroid dehydratase as key enzyme has not been systematically studied. Here, combined proteomic, bioinformatic and functional analyses of the Δ4,6-variant in Sphingobium sp. strain Chol11 were performed. They revealed a degradation of the steroid rings similar to the Δ1,4-variant except for the elimination of the 7-OH as key difference. In contrast, differential production of the respective proteins revealed a putative gene cluster for side-chain degradation encoding a CoA-ligase, an acyl-CoA dehydrogenase, a Rieske monooxygenase, and an amidase, but lacking most canonical genes known from other steroid-degrading bacteria. Bioinformatic analyses predicted the Δ4,6-variant to be widespread among the Sphingomonadaceae, which was verified for three type strains which also have the predicted side-chain degradation cluster. A second amidase in the side-chain degradation gene cluster of strain Chol11 was shown to cleave conjugated bile salts while having low similarity to known bile-salt hydrolases. This study signifies members of the Sphingomonadaceae remarkably well-adapted to the utilization of bile salts via a partially distinct metabolic pathway.

Recent Progress Towards Synthesis of Furanosteroid Family of Natural Products

Furanosteroids are a class of novel pentacyclic fungal metabolites that share in common a furan ring, bridging at the 4 and 6 positions of the steroid skeleton. The strained furan...

Diels-Alder adduct of levoglucosenone with diene Dane approaches to estrogens

Levoglucosenone has established itself as a good Michael acceptor and a powerful dienophile in Diels-Alder reactions, dipolar cycloaddition and in a number of other transformations. In the Diels-Alder reactions of levoglucosenone with 1,3-dienes, chiral derivatives of cyclohexene are obtained, which are valuable products for the synthesis of natural compounds. We previously studied the reaction of the interaction of levoglucosenone with Dane diene under catalytic, thermal conditions, at ultrahigh pressures and microwave irradiation. It was found that as a result of the reaction, 2 adducts are formed – (1S,2S,15S,17R)-9-methoxy-18,20-dioxapentacyclo[15.2.1.02,15.0.5,14.06,11]icosa-4,6,8, 10-tetraen-16-one and its isomer, the product of the double bond migration is (1S,2S,14S,15S,17R)-9-methoxy-18,20-dioxapentacyclo[15.2.1.02,15.0.5, 14.06,11]icosa-5(14), 6,8,10-tetraen-16-one. In this work, we have developed methods for the transformation of these Diels-Alder adducts in approaches to compounds with a steroid skeleton. Thus, based on the obtained Diels-Alder adducts, optically active hydrazone was synthesized. An optimal method for deoxygenation of a keto group proceeding by aromatization of cycle B in (1S,2S,14S,15S,17R)-9-methoxy-18,20-dioxapenta-cyclo[15.2.1.02,15.0.5,14.06,11]icosa-5(14),6,8,10-tetraen-16-one, converting it to sulfide, followed by boiling in the presence of Raney nickel. The resulting compound, 9-methoxy-18,20-dioxapentacyclo-[15.2.1.02,15.0.5, 14.06,11]icosa-5(14),6,8,10,12-pentaenone, is a promising synthetic block for use in the synthesis of estrogen – equilenin. The biological activity of the synthesized compounds was predicted using the PASS computer program, which resulted in the identification of derivatives that are promising for the study of antacid, anti-seborrheic, embryotoxic, and anti-cancer properties.

Crystal and molecular structures of boldenone and four boldenone steroid esters

Androsta-1,4-dien-17β-ol-3-one, also known as boldenone, is an anabolic-androgenic steroid derived from testosterone. The crystal structures of boldenone base, boldenone acetate, boldenone propionate, boldenone cypionate and a boldenone acetate polymorph obtained by high throughput screening were investigated. Hirshfeld surfaces and fingerprint plots breakdown revealed that the molecular packing in the crystals are driven by dominant H⋯H intermolecular contacts, followed by O⋯H/H⋯O contacts and to a lesser degree C⋯H/H⋯C contacts. The steroid skeleton rings, for all the reported compounds, adopt the following conformation: planar in A, chair in B and C, whereas C(13) envelope conformations are found for the five-membered D rings. The total lattice energies were calculated as a sum of four terms (Coulombic, polarization, dispersion, repulsion).