Further studies of the β-lactamases ofBacteroides species

The -lactamases of individual strains ofBacteroides fragilis, B. thetaiotaomicron, andB. melaninogenicus were examined to characterize their enzymatic activity and the relation between the periplasmic and cytoplasmic forms of the enzymes. K_m and V_max values indicate that all strains examined were very similar in terms of enzymatic activity with the antibiotics tested. Electrophoretic analysis and treatment with phospholipase D suggest the presence of a cytoplasmic form of the enzyme that is modified upon entry into the periplasmic space.     

Penicillinase activity in three strains ofClostridium butyricum

Three strains ofClostridium butyricum exhibited elevated minimal inhibitory concentrations (MICs) to penicillin (64–1,024 g/ml), ampicillin (32–256 g/ml), carbenicillin (128–1,024 g/ml), and oxacillin (32–64 g/ml). Cephalosporin/cephamycin agents were more active than penicillin drugs. All isolates were found to possess a -lactamase. The -lactamases were primarily cell associated during the logarithmic phase of growth. Stationary-phase cells released most of the enzyme into the culture medium. Cephalothin supplementation of broth cultures with concentrations equivalent to one-eighth of the MIC significantly increased the quantity of -lactamase synthesized. The -lactamases produced by these three isolates exhibited greatest activity with penicillin followed by ampicillin>cephaloridine>carbenicillin and oxacillin. No enzymatic activity was observed using cephalothin, cephalexin, cefazolin, cefoxitin, or cephamandole substrates. The -lactamases were inhibited by clavulanic acid and para-chloromurcuribenzoate and not inhibited by cloxacillin. Each enzyme exhibited an isoelectric point of 4.2.     

Factors Affecting the Toxic Effect of Tin on Estuarine Microorganisms

Inorganic tin (SnCl₄·H₂O) is toxic to microbial populations obtained from estuarine sediments plated on nutrient medium solidified with either agar or purified agar. The use of gelatin as a gelling agent decreased the apparent toxicity of tin, and toxicity was markedly reduced in medium solidified with silica gel. There was no evidence that toxic agar-tin complexes were involved. Cd, Cu, Pb, Ni, and Zn exhibited similar toxicity patterns; therefore, toxicity levels determined in the laboratory should be extrapolated to the environment with caution. The addition of cysteine to the medium had no effect on tin toxicity. Serine or 3-hydroxyflavone enhanced toxicity, while humic acids or gelatin inhibited toxicity. Replacement of SO₄²⁻ with NO₃⁻ did not alter tin toxicity, but replacement of Cl⁻ with NO₃⁻ decreased tin toxicity. Thus, the toxic effect(s) of tin depend as much on the chemical speciation of the metal as on the total concentration of the metal in the medium.     

A previously unrecognized Isidrogalvia (Liliaceae) from Bolivia

Isidrogalvia longiflora, a new combination based onAsagraea longiflora, is proposed. It is the first record ofIsidrogalvia from Bolivia.     

“That land of flowers,swamps and alligators”: S. B. Buckley’s 1843 trip up the St. Johns River,Florida

In 1843 S. B. Buckley (1809–1884) traveled up the St. Johns River, Florida in search of plants, shells, and possibly other natural history objects. Buckley encountered many difficulties in interior Florida and his trip did not live up to his original expectations. It was unfortunate that the took years to distribute his plant specimens, since few botanists or naturalists had preceded him into that poorly explored region.     

Interactions of surfactin,a biosurfactant fromBacillus subtilis,with inorganic cations

Summary The properties of surfactin, a biosurfactant lipopeptide, were highly modified in the presence of inorganic cations. The micellization of surfactin was favoured by monovalent and, especially by divalent cations with a modification of the molecular area at the air-water interface. Haemolysis of erythrocytes by surfactin was enhanced by low concentrations of divalent cations with an increase of the binding of the lipopeptide to membrane. Inorganic ions induced conformational rearrangements probably due to ion-surfactin associations which modify the surface-active properties.     

Luteinizing hormone stimulates the production of prostacyclin by isolated ovarian cell invitro

Granulosa cells isolated from mature Graafian follicles of swine produced significant quantities of immunoreactive 6-keto-PGF₁α under chemically defined conditions in vitro. Luteinizing hormone elicited a dose-dependent stimulation of 6-keto-PGF₁α accumulation, but follicle stimulating hormone, prolactin, L-epinephrine, estradiol-17B, or PGE₂ were devoid of effect. The time-dependent in vitro production of 6-keto-PGF₁α by ovarian cells was susceptible to inhibition by indomethacin, U-51506, cycloheximide, and actinomycin D. These observations implicate granulosa cells in the specific and hormonally regulated production of prostacyclin.     

Variation and taxonomy of Aesculus pavia L. (Hippocastanaceae) in Texas

The status of Aesculus pavia var. flavescens, a set of yellow-flowered populations endemic to the Edwards Plateau of central Texas, was evaluated on the basis of comparative morphology, geography, flowering phenology, and pollination ecology. Plants of typical A. pavia have red, tubular flowers with exserted stamens and are effectively pollinated by ruby-throated hummingbirds. Plants of var. flavescens have yellow, campanulate flowers with included stamens that can be pollinated effectively by large bees. These ethological reproductive isolating mechanisms are further augmented by a difference in flowering time between the two sets of populations and by geographical restriction of the yellow-flowered plants to localities on the Edwards Plateau. The yellow and red-flowered plants constitute two morphologically distinct groups, despite evidence of limited introgression in counties along the Balcones Escarpment. A yellow-flowered plant discovered in coastal east Texas may indicate the mechanism by which var. flavescens originated, but this plant is much more closely comparable to typical red-flowered var. pavia than to the yellow-flowered plants on the Edwards Plateau. An evolutionary history of section Pavia of Aesculus is presented, and it is concluded that the yellow-flowered plants of central Texas are best regarded as a taxonomic variety.