Nif-hybrids of Enterobacter: selection for nif gene integration with chlorate

The nif gene group from Klebsiella can be transferred into Enterobacter cloacae by conjugation using Escherichia coli donor cells carrying the composite self-transmissible nif-plasmid pRD1. A small fraction of the hybrids obtained is stable upon prolonged passaging without selection. Their stability is due to integration of pRD1 into the chromosome. Such integration hybrids were chlorate resistant, and nitrate reductase negative, which indicated that integration preferentially occurred within one of the genes for the production or functioning of this enzyme. Chlorate resistance could, therefore, be used to select for additional nitrate reductase-negative sublines with pRD1 in their chromosome. Such sublines have been analyzed further for the presence of nif genes, other pRD1 markers, and for stability. In all except one the complete plasmid seems to have been integrated. Some tend to revert to nitrate utilisation (chlorate sensitivity).     

Advantages of arthroscopy of the knee joint]

Arthroscopic surgery causes considerably less soft tissue damage than conventional surgery. As the result of the development of an optical system employed with a chip camera and a video chain arthroscopic knee surgery can be ideally documented with excellent picture quality. Besides the advantage of soft-tissue sparing procedures, diagnosis is substantially improved and operative procedures can be kept to a minimum. This means, in particular in the case of meniscus procedures, that only the damaged areas are removed, this minimising changes to the biomechanics of the knee. The technical equipment, the arthroscopic surgery technic and the advantages of the knee arthroscopy are discussed.     

Location and dynamics of alpha-tocopherol in model phospholipid membranes with different charges.

Studies were made on the position and dynamics of the OH-group of alpha-tocopherol in phospholipid membranes. There was no difference in the spin-lattice (T1) relaxation times at the 5a-position of alpha-tocopherol labeled with 13C- or C19F3-determined from the nuclear magnetic resonance (NMR) spectra of liposomes positively charged with stearylamine (SA) and negatively charged with dicetylphosphate (DCP). The zeta-potentials of egg yolk phosphatidylcholine (EYPC) liposomes with and without SA or DCP were not affected by incorporation of 20 mol% alpha-tocopherol, though incorporation of 10 mol% ascorbyl-palmitate decreased the zeta-potentials of EYPC and EYPC-SA liposomes. The P==O stretching band (1235 cm-1) of the phosphate group and C==O stretching band (1734 cm-1) of the acyl ester linkage in dimyristoylphosphatidylcholine (DMPC) liposomes, measured by Fourier transform-infrared (FT-IR) spectroscopy, were not changed by incorporation of alpha-tocopherol. These results suggest that no specific interaction occurred between the OH-group of alpha-tocopherol and the polar interfacial region of the bilayer. The dynamic quenching effects of n-(N-oxy-4,4'-dimethyloxazolidine-2-yl)stearic acids (n-NSs) on the intrinsic fluorescence of alpha-tocopherol were in the order 5-NS > 7-NS = 12-NS > 16-NS. Acrylamide, a water-soluble fluorescence quencher with a very low capacity to penetrate through phospholipid bilayers, had very low quenching efficiency. These results indicate that the bulk of the chromanol moiety of alpha-tocopherol is located in a position close to that occupied by the nitroxide group of 5-NS in the membranes and is poorly exposed at the membrane surface.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental Mycoplasma gallisepticum infections in captive-reared wild turkeys

The effects of Mycoplasma gallisepticum (MG) infections on egg production, fertility, and hatchability were studied in captive-reared wild turkeys (Meleagris gallopavo). Three groups of adult birds, each consisting of four hens and two toms, were exposed to MG by the respiratory route at the beginning of their breeding season. Fourteen control birds received sterile growth medium. Although no mortality of infected or control birds occurred, egg production during the first breeding season after infection was reduced. The mean number of eggs/hen/day produced by infected groups the first breeding season postexposure (PE) was significantly lower than the control value. The mean number of eggs produced daily by the same hens 1 yr later was unaffected by MG infection. The percentage of fertile eggs produced by infected groups was slightly reduced in both the first and second breeding seasons PE. Hatchability of fertile eggs from infected hens was significantly lower than eggs from control hens. Productivity may be impaired if MG infections occur in free-ranging wild turkey populations.     

Habitat characteristics contributing to local occupancy and habitat use in rock pool <Emphasis Type="Italic">Daphnia</Emphasis> metapopulations

The effects of invasive macrophytes, water level fluctuations and predation on freshwater unionids Pyganodon grandis and Utterbackia imbecillis were studied in three small impoundments in Northeastern Texas in 2003–2005. Mussel density was sampled with quadrats. Mortality, associated with the water level fluctuations and predation, was estimated by collecting dead shells on the shore at about two month intervals. In two ponds, horizontal distribution of unionids was limited by dense beds of invasive and noxious macrophytes (mainly Eurasian watermilfoil Myriophyllum spicatum and American lotus Nelumbo lutea): mussel densities were significantly lower in these macrophyte beds (P < 0.001). In the third pond with the lowest density of macrophytes (stonewort Chara sp.), unionids were distributed more evenly, and the average unionid biomass was the highest among all ponds studied. Vertical distribution of unionids in all ponds was likely limited by low oxygen at depth >2 m. The total amount of shells found on the shore per year varied from 0.1% to 28% of the total population in the pond and was negatively correlated with water level (r = −0.72 to −0.81, P < 0.005). Mammalian predators consumed up to 19% of the total unionid population and predation was facilitated by water level fluctuations. Handling editor: K. Martens     

Photochemical covalent binding of urocanic acid to polynucleic acids

Photolysis of E-[ring-2-14C]urocanic acid (UA) with native or denatured calf thymus DNA leads to covalent binding of the radiolabel to the nucleic acid. A similar observation is made upon photolysis of the labeled UA with the polyribonucleotides, in which case a strong preference is observed for binding to poly[U]. DNA or poly[U], which had been reacted with UA and purified by dialysis and multiple precipitations, releases UA upon further irradiation with 254 nm light (as expected for cyclobutane adducts). Quantum efficiencies for binding of the UA to native DNA have been measured at 308 and 266 nm and are 0.30 x 10(-5) and 1.3 x 10(-4), respectively, at comparable reactant concentrations. The large increase at the shorter wavelength (where DNA absorption is more competitive) is taken as evidence for the primary role of a DNA excited state in initiating the binding reaction(s).