Microbial response to drought in a Texas highplains shortgrass prairie

The population of the microbial flora of a mixed blue gramma grass (Bouteloua gracilis H. B. K.) and prickly pear (Opuntia polyacantha Haw.) prairie near Amarillo, Texas, was studied during 1971 after a severe drought. Bacteria, fungi, and algae were estimated by plate count and terminal dilution procedures. Rates of grass and paper decomposition were determined. The microbial flora of soil associated with bovine-grazed grass did not differ significantly from the flora associated with ungrazed grass, either qualitatively or quantitatively. During drought, a greater number of fungi were found in soil associated with prickly pear than in that associated with blue gramma grass. The microbial biomass decreased one full log between the surface and a depth of 50 cm, and the percentage of anaerobes increased with depth. The maximum numbers of fungi and algae detected were 8 × 10⁵ and 6 × 10⁴/g respectively. A linear relationship existed between the microbial biomass and soil moisture. The maximum number of aerobic, heterotrophic bacteria detected was 1.5 × 10⁸ viable cells per g of soil.     

Mechanisms of action of histidinol dehydrogenase and UDP-Glc dehydrogenase. Evidence that the half-reactions proceed on separate subunits.

Histidinol dehydrogenase and UDP-Glc dehydrogenase catalyze 4-electron dehydrogenations that convert primary alcohol groups to the corresponding acids. Both reactions proceed in two distinct steps involving the oxidation of the primary alcohol to a bound form of the intermediate aldehyde, followed by oxidation of this to the corresponding acid. The enzymes have subunit structure, the former is made up of two subunits and the latter of six (beef liver enzyme). Evidence is presented that the two half-reactions proceed independently of the overall reaction. Histidinol dehydrogenase preparations that approach total dissociation into subunits also approach total inhibition of the overall reaction, while the second half reaction is completely unaffected and 50% of the first half-reaction survives. Further, the fraction of overall activity surviving in partially dissociated preparations follows the weight fraction of residual dimer. UDP-Glc dehydrogenase behaves in an analogous fashion. These data are interpreted on the basis that both enzymes function by carrying out first oxidation step at a site on one subunit and then pass the intermediate to a vicinal site on the adjacent subunit, where the reaction is completed.     

The Notch amino terminus regulates protein levels and Delta-induced clustering of Drosophila Notch receptors

Notch signaling is required for the development of almost all animal tissues. It is a cell surface receptor that generates intracellular signals in response to Delta binding its extracellular domain. Notch response to Delta is affected by mutations in its extracellular domain outside of the Delta binding region. One such region is the Notch amino terminus. Mutations in this region are associated with developmental defects. How a mutation in the Notch amino terminus affects Notch function is unknown. We explored this issue in Drosophila melanogaster. We report that Notch receptors mutated in the amino terminus accumulate to abnormal levels, are deficient in Delta induced receptor clustering, and exhibit reduced rate of internalization and signaling. Notch receptors lacking the whole or the carboxy-terminal half of the intracellular domain are defective in internalization but not in clustering or accumulation. None of the other mutated Notch receptors showed defects in clustering, accumulation, or internalization. These observations suggest that the Notch amino terminus regulates Notch levels and clustering, which could affect the rate of Notch signaling and down-regulation.     

The Caulobacter crescentus CgtAC protein cosediments with the free 50S ribosomal subunit

The Obg family of GTPases is widely conserved and predicted to play an as-yet-unknown role in translation. Recent reports provide circumstantial evidence that both eukaryotic and prokaryotic Obg proteins are associated with the large ribosomal subunit. Here we provide direct evidence that the Caulobacter crescentus CgtA(C) protein is associated with the free large (50S) ribosomal subunit but not with 70S monosomes or with translating ribosomes. In contrast to the Bacillus subtilis and Escherichia coli proteins, CgtA(C) does not fractionate in a large complex by gel filtration, indicating a moderately weak association with the 50S subunit. Moreover, binding of CgtA(C) to the 50S particle is sensitive to salt concentration and buffer composition but not guanine nucleotide occupancy of CgtA(C). Assays of epitope-tagged wild-type and mutant variants of CgtA(C) indicate that the C terminus of CgtA(C) is critical for 50S association. Interestingly, the addition of a C-terminal epitope tag also affected the ability of various cgtA(C) alleles to function in vivo. Depletion of CgtA(C) led to perturbations in the polysome profile, raising the possibility that CgtA(C) is involved in ribosome assembly or stability.     

Responses of grassland production to single and multiple global environmental changes

In this century, increasing concentrations of carbon dioxide (CO₂) and other greenhouse gases in the Earth's atmosphere are expected to cause warmer surface temperatures and changes in precipitation patterns. At the same time, reactive nitrogen is entering natural systems at unprecedented rates. These global environmental changes have consequences for the functioning of natural ecosystems, and responses of these systems may feed back to affect climate and atmospheric composition. Here, we report plant growth responses of an ecosystem exposed to factorial combinations of four expected global environmental changes. We exposed California grassland to elevated CO₂, temperature, precipitation, and nitrogen deposition for five years. Root and shoot production did not respond to elevated CO₂ or modest warming. Supplemental precipitation led to increases in shoot production and offsetting decreases in root production. Supplemental nitrate deposition increased total production by an average of 26%, primarily by stimulating shoot growth. Interactions among the main treatments were rare. Together, these results suggest that production in this grassland will respond minimally to changes in CO₂ and winter precipitation, and to small amounts of warming. Increased nitrate deposition would have stronger effects on the grassland. Aside from this nitrate response, expectations that a changing atmosphere and climate would promote carbon storage by increasing plant growth appear unlikely to be realized in this system.     

A case series on the potential effect of omega-3-fatty acid supplementation on 24-h heart rate variability and its circadian variation in children with attention deficit (hyperactivity) disorder

Attention deficit disorder with and without hyperactivity (ADHD) in children is associated with decreased 24-h heart rate variability (HRV). Previous research has shown that supplementation of omega-3-fatty acid increases HRV. Here, we aimed to investigate whether the supplementation of omega-3-fatty acids would increase 24-h HRV in an uncontrolled case series of children with ADHD. HRV was recorded in 18 children and adolescents (age 13.35 ± 2.8 years) before and after omega-3 supplementation. Preliminary results indicate that omega-3 supplementation in children with AD(H)D may reduce mean heart rate and increase its variability. Future studies would do well to implement randomized, placebo-controlled designs with greater methodological rigor.     

The Genome Sequence DataBase (GSDB): meeting the challenge of genomic sequencing.

The genome sequence database (GSDB) is a complete, publicly available relational database of DNA sequences and annotation maintained by the National Center for Genome Resources (NCGR) under a Cooperative Agreement with the US Department of Energy (DOE). GSDB provides direct, client- server access to the database for data contributions, community annotation and SQL queries. The GSDB Annotator, a multi-platform graphic user interface, is freely available. Automatically updated relational replicates of GSDB are also freely available.