Non-nutritional stress acclimation of mycorrhizal woody plants exposed to drought.

Mycorrhizal enhancement of drought resistance of two woody plant species, loblolly pine (Pinus taeda L.) and rose (Rosa hybrida L. cv. Ferdy), occurred independently of phosphorus nutrition. Mycorrhizae tended to alter root morphology and carbon allocation patterns of shoots and roots. Increased drought resistance of mycorrhizal plants was in part attributed to drought-induced colonization by mycorrhizae and the ability of the mycorrhizal plants to maintain high transpiration rates as a result of greater lateral root formation and lower shoot mass (in ectomycorrhizal loblolly pine), and a higher root/shoot ratio and leaf abscission (in endomycorrhizal roses). Neither the endo- nor ectomycorrhizal symbionts affected osmotic adjustment of droughted plants.

Effect of pH on bile salt degradation by mixed fecal cultures.

Stoll specimens from 3 healthy volunteers were cultured under an-aerobic conditions in brain heart infusion broth with and without the addition of cholate, deoxycholate of chenodeoxycholate. The initial pH of the medium was adjusted to 5.5, 6.3, 7.3 (unadjusted), 8.0, and 9.0. Cell-free extracts prepared from the resulting bacterial growth contained increased levels of NAD- and NADP-dependent 3alpha-, 7alpha-, and 12alpha-hydroxysteroid oxidoreductases when the initial pH was 8.0 or 9.0 and depressed levels of these activities when the initial pH was 5.5 or 6.3 (as compared to control values obtained at 7.3). At pH 5,5 all activities except NAD-dependent 7alpha-hydroxysteroid oxidoreductase were absent. A powerful selective effect was imposed on NAD-dependent 7alpha-hydroxysteroid oxidoreductase when deoxycholate or chenodeoxycholate were incorporated into or chenodeoxycholate were incorporated into the medium. Thin-layer chromatography of either extracts of cholate-containing, acidified spent bacterial medium showed alkaline or neutral (optimal at pH 8). The precent hydroxyl group estimations at the 3alpha-, 7alpha-, and 12alpha-positions revealed an increase in disappearance of OH groups at all three positions with increasing initial pH value. The order of extent of bioconversion was 7alpha-OH greater than 3alpha-OH; at pH 8 AND 9, approximately 90% 7alpha-OH bioconversion was observed. Spent bacterial media and a number of commercial secondary bile salts were all negative in the Ames' assay for mutagenicity.

NAD-dependent 3alpha- and 12alpha-hydroxysteroid dehydrogenase activities from Eubacterium lentum ATCC no. 25559.

Eubacterium lentum (ATCC No. 25559) was shown to contain 3alpha-and 12alpha-hydroxysteroid dehydrogenases both of which were NAD-dependent and active against conjugated and unconjugated bile salts. In addition, the 3alpha-hydroxysteroid dehydrogenase was active against members of the Androstan series containing a 3alpha-hydroxyl group regardless of the stereo-orientation of the 5-H-. No measurable activity against 7alpha-, 7beta-, 11beta-, or 17beta-hydroxyl groups was demonstrated. The growth of E. lentum and the production of 3alpha- and 12alpha-hydroxysteroid dehydrogenases were greatly enhanced by the addition of L-, D- or DL-arginine to the medium. Yields of hydroxysteroid dehydrogenase were optimal in the range of 0.50-0.75% arginine; however, the growth of the organisms was further enhanced at arginine concentrations greater than 0.75%. The 12alpha-hydroxysteroid dehydrogenase was heat labile and could be selectively inactivated by heating at 50 degrees C for 45 min. Both the heated enzyme preparation (containing only 3alpha-hydroxysteroid dehydrogenase) and the unheated enzyme preparation (containing 3alpha- and 12alpha-hydroxysteroid dehydrogenases) were useful in the spectrophotometric quantification of bile salts. The optimal pH values for 3alpha- and 12alpha-hydroxysteroid dehydrogenases were 11.3 and 10.2, respectively. Kinetic studies have Km estimates of 2.10(-5) M and 1.0.10(-4) M with 3alpha,7alpha-dihydroxy-5beta-cholanoyl glycine and 7alpha,12alpha-dihydroxy-5beta-cholanoate for the two respective enzymes.

Bile salt degradation by nonfermentative clostridia.

Eight strains of nonfermentative clostridia were characterized on the basis of their intracellular nicotine adenine dinucleotide- and nicotinamide adenine dinucleotide phosphate-dependent hydroxysteroid dehydrogenase (HSDH) content, ability to deconjugate taurocholate, growth characteristics, and metabolic products, including utilization of lactate and pyruvate. Two cultures of Clostridium sporosphaeroides (representing one strain obtained from two different sources), one strain of Clostridium irregularis, four strains of an unnamed species (Clostridium group SPH-1), and one strain of an unnamed species (Clostridium group P) were studied. Both cultures of C. sporosphaeroides contained low amounts of 7alpha-HSDH; C. irregularis contained only a low amount of 3alpha-HSDH. All four strains of Clostridium SPH-1 contained both 12alpha- and 7alpha-HSDH in the ratio of approximately 10:1. The strain of Clostridium group P contained only 12alpha-HSDH and was devoid of any other bile salt oxidoreductases. The enzyme preparation from Clostridium group P was useful in spectrophotometric quantitative studies of 12alpha-OH groups. Correlation of bile salt degradative activities with other phenotypic tests for characterization of and differentiation among such organisms is discussed.