Dehydroxylation of 16 alpha-hydroxyprogesterone by fecal flora of man and rat

16 alpha-Hydroxyprogesterone, precursor of biliary 16 alpha-hydroxypregnanolone, was incubated with mixed fecal flora of humans and rats. The major steroid metabolite formed in both systems was 3 alpha-hydroxy-17 alpha-pregnan-20-one. These results demonstrated that the fecal flora reduced the delta 4-3 keto structure, removed the hydroxy group at C-16 and isomerized the side chain from the beta to the alpha configuration. Ring-A reduction of the substrate resulted in a 5 beta-compound with human flora and a 5 alpha-product with rat bacteria. The prevalence of 16 alpha-dehydroxylating organisms varied considerably in human fecal flora and was approximately 10(5)/g of feces in the three rats tested. Rat fecal flora dehydroxylated 16 alpha-hydroxyprogesterone after 4-5 days incubation at 37 degrees C, at pH 6.5-7.5, and with a substrate concentration of 20-80 microgram/ml (optimal condition). Preliminary evidence suggests that 16 alpha-dehydroxylase is exclusively of bacterial origin and is synthesized by an obligate anaerobe.

7 alpha-Dehydroxylation of cholic acid by cell extracts of Eubacterium species V.P.I. 12708

NADH:flavin oxidoreductase and 7 alpha-dehydroxylase were induced 5- and 90-fold, respectively, by cholic acid in cultures of Eubacterium species V.P.I. 12708. Assays of 7 alpha-dehydroxylase activity in the presence of various cofactors revealed that optimal activity was obtained in the presence of NAD+ plus FADH2. The pH optima of 7 alpha-dehydroxylase activity in whole cells and cell extracts were 7.0. The similar induction pattern of these two enzymes and the apparent cofactor requirements for 7 alpha-dehydroxylation suggest a relationship between 7 alpha-dehydroxylase and NADH:flavin oxidoreductase.

Characterization of a corticosteroid 21-dehydroxylase from the intestinal anaerobic bacterium, Eubacterium lentum

An oxygen-sensitive corticosteroid 21-dehydroxylase has been characterized in cell extracts of Eubacterium lentum. The enzyme was highly specific for corticosteroids containing and alpha-ketol structure and required FMNH2 or reduced benzyl viologen for activity. The enzyme used deoxycorticosterone, deoxycortisol, dehydrocorticosterone, and corticosterone as substrates. Substrate saturation kinetics using [3H]corticosterone yielded an apparent Km of 7.35 microM and a Vmax of 15.4 nmol (11 beta-[3H]hydroxyprogesterone) formed per hr x mg protein-1. 21-Dehydroxylase activity was inhibited by both water-soluble and lipophilic metal ion chelators. NADH: flavin oxidoreductase and 21-dehydroxylase activities were separated by anaerobic DEAE-cellulose and Sepharose 6B chromatography. 21-Dehydroxylase had a relative weight of 582,000 as determined by Sepharose 6B chromatography. There was a 7-fold increase in the rate of 21-dehydroxylation of [3H]deoxycorticosterone in whole cell suspensions of E. lentum sparged with H2 as compared to argon gas.

Characterization of a NADH:flavin oxidoreductase induced by cholic acid in a 7 alpha-dehydroxylating intestinal Eubacterium species

A NADH:flavin oxidoreductase was partially purified (seven-fold) from an intestinal Eubacterium species V.P.I. 12708 using Bio-Gel A 0.5-M and DEAE-cellulose column chromatography. Enzyme activity was measured spectrophotometrically at 340 nm under anaerobic conditions. A molecular weight of 260 000 was estimated by gel filtration chromatography. The partially purified enzyme preparation exhibited single displacement kinetics with respect to the substrates NADH and FAD. The pH optimum under these conditions was 6.8. NADH:flavin oxidoreductase showed an absolute specificity for NADH as electron donor. However, methylene blue, 2,6-dichlorophenolindophenol, K3Fe(CN)6, menadione, riboflavin, FMN and molecular oxygen served as alternate electron acceptors with varying degrees of efficiency. Acriflavin, rotenone, o-phenanthroline, p-chloromercuribenzoate, dicoumarol and 2,4-dinitrophenol inhibited enzyme activity. Surprisingly, 0.1 mM cholic acid, but not 0.1 mM deoxycholic acid, rapidly induced NADH:flavin oxidoreductase activity in growing cultures.

Characterization of a pyridine nucleotide-nonspecific glutamate dehydrogenase from Bacteroides thetaiotaomicron

An oxidized nicotinamide adenine dinucleotide phosphate/oxidized nicotinamide adenine dinucleotide (NADP+/NAD+) nonspecific L-glutamate dehydrogenase from Bacteroides thetaiotaomicron was purified 40-fold (NADP+ or NAD+ activity) over crude cell extract by heat treatment, (NH4)2SO2 fractionation, diethylaminoethyl-cellulose, Bio-Gel A 1.5m, and hydroxylapatite chromatography. Both NADP+- and NAD+-dependent activities coeluted from all chromatographic treatments. Moreover, a constant ratio of NADP+/NAD+ specific activities was demonstrated at each purification step. Both activities also comigrated in 6% nondenaturing polyacrylamide gels. Affinity chromatography of the 40-fold-purified enzyme using Procion RED HE-3B gave a preparation containing both NADP+- and NAD+-linked activities which showed a single protein band of 48,5000 molecular weight after sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis. The dual pyridine nucleotide nature of the enzyme was most readily apparent in the oxidative direction. Reductively, the enzyme was 30-fold more active with reduced NADP than with reduced NAD. Nonlinear concave 1/V versus 1/S plots were observed for reduced NADP and NH4Cl. Salts (0.1 M) stimulated the NADP+-linked reaction, inhibited the NAD+-linked reaction, and had little effect on the reduced NADP-dependent reaction. The stimulatory effect of salts (NADP+) was nonspecific, regardless of the anion or cation, whereas the degree of NAD+-linked inhibition decreased in the order to I- greater than Br- greater than Cl- greater than F-. Both NADP+ and NAD+ glutamate dehydrogenase activities were also detected in cell extracts from representative strains of other bacteroides deoxyribonucleic acid homology groups.

Bile acid induction specificity of 7 alpha-dehydroxylase activity in an intestinal Eubacterium species

The addition of cholic acid to growing cultures of Eubacterium species V.P.I. 12708 caused a 25 and 46-fold increase in 7 alpha-dehydroxylation activity using cell extracts or whole cell suspensions, respectively. Bile acid conversion rates using either [14C]-cholic acid or [14C]-chenodeoxycholic acid as substrates increased at approximately the same rate when either cholic or chenodeoxycholic acid was added to growing cultures as inducer. The induction of 7 alpha-dehydroxylase activity was highly specific requiring a free C-24-carboxyl group and an unhindered 7 alpha-hydroxy group on the B ring of the steroid nucleus. Unexpectedly, cholic acid also rapidly induced NADH:flavin oxidoreductase activity in growing cultures of this bacterium.

Characterization of a C21 neutral steroid hormone transforming enzyme, 21-dehydroxylase, in crude cell extracts of Eubacterium lentum

A strain of the obligate anaerobe, Eubacterium lentum, isolated from human feces, catalyzes the 21-dehydroxylation of 11-deoxycorticosterone to progesterone. A quantitative radiochromatographic assay was developed to measure 21-dehydroxylase activity in cell extracts. Maximum enzyme activity in cell extracts required both a reduced pyridine nucleotide and an oxidized flavin coenzyme. However, photochemically reduced flavin (FMNH2) could replace the requirement for NAD(P)H plus oxidized flavin. NAD(P)H : flavin (either FMN or FAD) oxidoreductase activity was detected spectrophotometrically in cell extracts assayed under anaerobic conditions. 21-Dehydroxylase was active from pH 5.4 to 8.5 with an apparent optimum between 6.4 and 6.8 using mixtures of NADH plus FMN as coenzymes. The substrate concentration at half-maximal reaction velocity was 8.0 microM and a specific acitivity of 5.8 nmol [3H]progesterone formed . h-1 . mg-1 protein was determined using [3th]deoxycorticosterone as substrate. Atabrine, rotenone, acriflavin, and 2,4-dinitrophenol (all at 1 mM) inhibited 21-dehydroxylase activity in cell extracts by 25, 24, 35 and 84%, respectively. These results suggest that 21-dehydrogenase may be coupled to a NAD(P)H : flavin oxidoreductase system in E. lentum.

7alpha-Dehydroxylation of cholic acid and chenodeoxycholic acid by Clostridium leptum

The rate of 7alpha-dehydroxylation of primary bile acids was quantitatively measured radiochromatographically in anaerobically washed whole cell suspensions of Clostridium leptum. The pH optimum for the 7alpha-dehydroxylation of both cholic and chenodeoxycholic acid was 6.5-7.0. Substrate saturation curves were observed for the 7alpha-dehydroxylation of cholic and chenodeoxycholic acid. However, cholic acid whole cell K0.5 (0.37 micron) and V (0.20 mumol hr-1mg protein-1) values differed significantly from chenodeoxycholic acid whole cell K0.5 (0.18 micron) and V (0.50 mumol-1 hr-1 mg protein-1). 7alpha-Dehydroxylation activity was not detected using glycine and taurine-conjugated primary bile acids, ursodeoxycholic acid, cholic acid methyl ester, or hyocholic acid as substrates. Substrate competition experiments showed that cholic acid 7 alpha-dehydroxylation was reduced by increasing concentrations of chendeoxycholic acid; however, chenodeoxycholic acid 7alpha-dehydroxylation activity was unaffected by increasing concentrations of cholic acid. A 10-fold increase in cholic and 7alpha-dehydroxylation activity occurred during the transition from logarithmic to stationary phase growth whether cells were cultured in the presence or absence of sodium cholate. In the same culture, a similar increase in chenodeoxycholic acid 7alpha-dehydroxylation was detected only in cells cultured in the presence of sodium cholate. These results indicate the possible existence of two independent systems for 7alpha-dehydroxylation in C. Leptum.

Synthesis of guanosine tetra- and pentaphosphates by the obligately anaerobic bacterium Bacteroides thetaiotaomicron in response to molecular oxygen

Guanosine 5'-diphosphate 3'-diphosphate (ppGpp) and guanosine 5'-triphosphate 3'-diphosphate (pppGpp) were detected in formic acid extracts of air-exposed culutres of Bacteroides thetaiotaomicron. The identification of ppGpp and pppGpp in B. thetaiotaomicron was based on the following results: (i) cochromatography of 32P-labeled hyperphosphorylated nucleotides in two different two-dimensional solvent systems with authentic ppGpp and pppGpp; (ii) incorporation of [3H]guanosine into the putative ppGpp and pppGpp; (iii) alkaline lability; and (iv) resistance, to periodate oxidation. There was a marked increase in the concentration of ppGpp and pppGpp after shift from anaerobic to aerobic conditions, and accumulation of both ppGpp and pppGpp was blocked under these conditions by pretreatment of the culture with rifampin or tetracycline. Growth and incorporation of [3H]guanosine, [3H]tymidine, [14C]succinate, and L-[35S]methionine into macromolecules were inhibited immediately upon exposure to air. The accumulation of ppGpp and pppGpp in B. thetaiotaomicron upon exposure to air may represent a novel signal for synthesis of these compounds.

Characterization of 7-alpha-dehydroxylase in Clostridium leptum

7-alpha-Dehydroxylation of primary bile acids was demonstrated radiochromatographically in whole cells of Clostridium leptum but was not observed in intestinal Bacteroides species. Activity of 7-alpha-Dehydroxylase was detected within a pH range of 5 to 9 and was 8-fold higher in specific activity in cell cultures in the presence of 0.1 mM sodium cholate than in its absence. 7-alpha-Dehydroxylase activity in whole cells was markedly inhibitied by 2,4-dinitrophenol, carbonyl-cyanide-m-chlorophenylhydrazine, and dicyclohexylcarbodiimide. A hypothesis concerning the dietary regulation of 7-alpha-dehydroxylating intestinal anaerobic bacteria is presented.

Partial purification and characterization of NAD-dependent 7alpha-hydroxysteroid dehydrogenase from Bacteroides thetaiotaomicron

A NAD-dependent 7alpha-hydroxysteroid dehydrogenase was purified 18-fold over the activity in crude cell extracts prepared from Bacteroides thetaiotaomicron NCTC 10852 using Bio-Gel A 1.5-M column chromatography. A molecular weight of 320 000 was estimated for the partially purified intact enzyme. Substrate saturation kinetics were performed using the 18-fold purified enzyme and the lowest Km values were obtained for 3alpha,7alpha-dihydroxy bile acid and bile salt substrates including chenodeoxycholic acid (Km 0.048 mM), glycochenodeoxycholic acid (Km 0.083 mM) and taurochenodeoxycholic acid (Km 0.059 mM). In contrast, 3alpha,7alpha,12alpha-trihydroxy bile acid and bile salts had higher Km values, i.e. cholic acid (Km 0.22 mM), glycoholic acid Km 0.32 mM) and taurocholic acid Km 0.26 mM). NAD had a Km value of 0.20 mM. The possible physiological significance of 7alpha-hydroxy bile acid oxidation to intestinal bacteroides strains was accessed by determining the rate of conversion of [14C]-cholic acid to 7-ketodeoxy[14C]cholic acid by whole cell suspensions under different incubation conditions. The rate of biotransformation of bile acid to keto-bile acid incubated anaerobically under N2 gas increased markedly when potential electron acceptors such as fumarate (10 mM) or menadione (4 mM) was added exogenously. These results suggest that bile acid oxidation reactions may be linked to energy-generating systems in this bacterium.

Cyclic adenosine 3',5'-monophosphate levels and activities of adenylate cyclase and cyclic adenosine 3',5'-monophosphate phosphodiesterase in Pseudomonas and Bacteroides

A modified Gilman assay was used to determine the concentrations of cyclic adenosine 3',5'-monophosphate (cAMP) in rapidly filtered cells and in the culture filtrates of Pseudomonas aeruginosa, Escherichia coli K-12, and Bacteroides fragilis. In P. aeruginosa cultures, levels of cAMP in the filtrate increased with the culture absorbance (3.5 to 19.8 X 10(-9) M) but did not vary significantly with the carbon source used to support growth. Intracellular concentrations (0.8 to 3.2 X 10(-5) M) were substantially higher and did not vary appreciably during growth or with carbon source. Sodium cAMP (5 mM) failed to reverse the catabolite repression of inducible glucose-6-phosphate dehydrogenase (EC 1.1.1.49) synthesis caused by the addition of 10 mM succinate. Exogenous cAMP also had no discernible effect on the catabolite repression control of inducible mannitol dehydrogenase (EC 1.1.1.67). P. aeruginosa was found to contain both soluble cAMP phosphodiesterase (EC 3.1.4.17) and membrane-associated adenylate cyclase (EC 4.6.1.1) activity, and these were compared to the activities detected in crude extracts of E. coli. B. fragilis crude cell extracts contain neither of these enzyme activities, and little or no cAMP was detected in cells or culture filtrates of this anaerobic bacterium.

Purification and characterization of bile salt hydrolase from Bacteroides fragilis subsp. fragilis

A high-molecular-weight (250 000) bile salt hydrolase (cholylglycine hydrolase, EC 3.5.-.-) was isolated and purified 128-fold from the "spheroplast lysate" fraction prepared from Bacteroids fragilis subsp. fragilis ATCC 25285. The intact enzyme had a molecular weight of approx. 250 000 as determined by gel infiltration chromatography. One major protein band, corresponding to a molecular weight of 32 500, was observed on 7% sodium dodecyl sulfate polyacrylamide gel electrophoresis of pooled fractions from DEAE-cellulose column chromatography (128-fold purified). The pH optimum for the 64-fold purified enzyme isolated from Bio-Gel A 1.5 M chromatography was 4.2 and bile salt hydrolase activity measured in intact cell suspensions had a pH optimum of 4.5. Substrate specificity studies indicated that taurine and glycine conjugates of cholic acid, chenodeoxycholic acid and deoxycholic acid were readily hydrolyzed; however, lithocholic acid conjugates were not hydrolyzed. Substrate saturation kinetics were biphasic with an intermediate plateau (0.2--0.3 mM) and a complete loss of enzymatic activity was observed at high concentration for certain substrates. The presence or absence of 7-alpha-hydroxysteroid dehydrogenase was absolutely correlated with that of bile salt hydrolase activity in six to ten strains and subspecies of B. fragilis.

Multiple forms of 7-alpha-hydroxysteroid dehydrogenase in selected strains of Bacteroides fragilis

Multiple forms of 7-alpha-hydroxysteroid dehydrogenase were detected in six of nine strains of Bacteroides fragilis. The enzymes differed with respect to pyridine nucleotide specificity, thermal stability, divalent metal cation requirement, and elution profilies from Sephadex G-200 columns. The nicotinamide adenine dinucleotide phosphate (NADP)-dependent enzyme required divalent metal cations, preferentially Mn-2+ (Km, 57 muM), for maximum catalytic activity. The NADP-dependent enzyme was labile at 65 C for 10 min, whereas the nicotinamide adenine dinucleotide (NAD)-dependent enzyme was stable at 65 C for 10 min. The specific activity of both the NAD- and NADP-dependent enzymes in crude extracts increased markedly (15- and 7.5-fold, respectively) during the transition from exponential- to stationary-phase growth in glucose medium containing 0.5 mM sodium cholate. The time course of apparent enzyme induction correlated temporally with the transformation of the 7-alpha-hydroxy group of cholate in the culture supernatant fluid. Both NAD- and NADP-dependent 7-alpha-hydroxysteroid dehydrogenase activities were found to be widely, but not universally, distributed in different strains and subspecies of B. fragilis. No NAD- or NADP-dependent 7-alpha-hydroxysteroid dehydrogenase activity could be detected in B. fragilis subsp. vulgatus Virginia Polytechnic Institute (VPI) no. 4245, subsp. thetaiotaomicron VPI 0061-1, or subsp. distasonis VPI 4243.

Transport and catabolism of D-fructose by Spirillum itersomii

Spirillum itersonii ATCC 12639 utilized d-fructose but neither d-glucose nor d-gluconate as a sole source of carbon and energy. The substrate saturation kinetics for d-fructose and d-glucose uptake by whole cells indicated the presence of a carrier-mediated transport system for d-fructose but not for d-glucose. The d-fructose uptake activity was induced (10- to 12-fold increase) during growth on d-fructose-Casamino Acids (CA) or d-glucose-CA medium, but not CA alone. d-Fructose uptake activity was stimulated by Na(+) or Li(+), but was inhibited by KCN, NaN(3), 2,4-dinitrophenol, and p-chloromercuribenzoate. High specific activities of glucokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydratase, and 2-keto-3-deoxy-6-phosphogluconate aldolase were detected in extracts of cells cultured on d-fructose-CA medium. These enzymatic activities were undetectable in extracts of cells grown in CA or succinate-CA medium. No decrease in the maximally induced specific activities of these enzymes occurred after the addition of succinate to cells during exponential growth on d-fructose-CA. Fructose 1,6-diphosphate aldolase and glucose-6-phosphate isomerase specific activities were approximately the same irrespective of cultural conditions. These results indicated that d-glucose was not utilized by cells of S. itersonii because this bacterium was impermeable to this hexose.