National initiatives in long-term care Koren, Mary Jane; Minnix, Larry; Yarwood, Bruce
Health Affairs,
2010 Mar-Apr, 2010-03-00, 20100301, Letnik:
29, Številka:
3
Journal Article
Urea-N is ubiquitous in soils, having both natural and anthropogenic sources. The enzyme urease catalyzes its hydrolysis to NH3 and is produced by plants and many soil microorganisms, but there are ...growing concerns related to possible urea-induced eutrophication of surface waters proximate to agricultural fields. Agronomic research has focused on the relationship between urea hydrolysis and soil physical or chemical properties, rather than on direct measurements of the microbial community and its population diversity, especially using quantification of genes that code for urease. We quantified bacterial and archaeal 16S rRNA, fungal ITS, and bacterial ureC gene copies as a function of physical and chemical soil properties. Soils were sampled from A and B horizons along a toposequence that comprised an agricultural field, a grassed field border, and a forested riparian zone in the Chesapeake Bay watershed of Maryland. The riparian zone soils contained the highest total number of genes among both A- and B-horizon soils. The soils were then experimentally altered in the laboratory to achieve a range of pH values between 3.1 and 7.1. Soil pH was chosen as a variable because it varies both naturally and due to agronomic practices, and it influences microbial community structure and function. Archaeal 16S rRNA extracted from the pH-adjusted soils did not show a consistent pattern of increase or decrease with changes in pH, while ITS was greatest at low pH and bacterial 16S and bacterial ureC were greatest at high pH. We measured higher urea hydrolysis rates and gene copy numbers in A-horizon soils than in B-horizon soils, and found that urea hydrolysis rate was significantly correlated with gene copies of bacterial 16S, ureC, and increased pH. This suggests that liming acid soils increases urea hydrolysis rates in part by encouraging the growth of microorganisms capable of producing urease.
•pH impacts urease gene numbers.•Bacterial urease gene numbers are correlated with urea hydrolysis rate.•1–20% of bacterial community was ureolytic in the studied soils.•No correlation found between archaeal 16S gene copy number and urea hydrolysis rate.•No correlation found between fungal ITS gene copy number and urea hydrolysis rate.
Dense hyphal mats formed by ectomycorrhizal (EcM) fungi are prominent features in Douglas-fir forest ecosystems, and have been estimated to cover up to 40% of the soil surface in some forest stands. ...Two morphotypes of EcM mats have been previously described: rhizomorphic mats, which have thick hyphal rhizomorphs and are found primarily in the organic horizon, and hydrophobic mats, which occur in the mineral horizon and have an ashy appearance. This study surveyed EcM mat and non-mat soils from eight early and late seral conifer forest stands at the H.J. Andrews Experimental Forest in western Oregon. EcM mats were classified by morphology and taxonomic identities were determined by DNA sequencing. A variety of chemical and biochemical properties, including enzymes involved in C, N, and P cycling were measured. Analysis was confined to a comparison of rhizomorphic mats colonizing the organic horizon with non-mat organic soils, and hydrophobic mats with non-mat mineral soils. Both the organic and mineral horizons showed differences between mat and non-mat enzyme profiles when compared on a dry weight basis. In the organic horizon, rhizomorphic mats had greater chitinase activity than non-mat soils; and in the mineral horizon, hydrophobic mats had increased chitinase, phosphatase, and phenoloxidase activity compared to the non-mat soil. The rhizomorphic mats had 2.7 times more oxalate than the non-mats and significantly lower pH. In the mineral horizon, hydrophobic mats had 40 times more oxalate and significantly lower pH than non-mat mineral soils. Microbial biomass C was not significantly different between the rhizomorphic mat and non-mat organic soils. In the mineral horizon, however, the hydrophobic mats had greater microbial biomass C than the non-mat soils. These data demonstrate that soils densely colonized by EcM fungi create a unique soil environment with distinct microbial activities when compared to non-mat forest soils.
We have determined which amino acids contribute to the pharmacophore of human C5a, a potent inflammatory mediator. A systematic mutational analysis of this 74‐amino acid protein was performed and the ...effects on the potency of receptor binding and of C5a‐induced intracellular calcium ion mobilization were measured. This analysis included the construction of hybrids between C5a and the homologous but unreactive C3a protein and site‐directed mutagenesis. Ten noncontiguous amino acids from the structurally well‐defined 4‐helix core domain (amino acids 1–63) and the C‐terminal arginine‐containing tripeptide were found to contribute to the pharmacophore of human C5a. The 10 mostly charged amino acids from the core domain generally made small incremental contributions toward binding affinity, some of which were independent. Substitutions of the C‐terminal amino acid Arg 74 produced the largest single effect. We also found the connection between these 2 important regions to be unconstrained.
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