Diversity within cyanobacterial mat communities in variable salinity meltwater ponds of McMurdo Ice Shelf, Antarctica

This study investigated the diversity of cyanobacterial mat communities of three meltwater ponds--Fresh, Orange and Salt Ponds, south of Bratina Island, McMurdo Ice Shelf, Antarctica. A combined morphological and genetic approach using clone libraries was used to investigate the influence of salinity on cyanobacterial diversity within these ecosystems without prior cultivation or isolation of cyanobacteria. We were able to identify 22 phylotypes belonging to Phormidium sp., Oscillatoria sp. and Lyngbya sp. In addition, we identified Antarctic Nostoc sp., Nodularia sp. and Anabaena sp. from the clone libraries. Fresh (17 phylotypes) and Orange (nine phylotypes) Ponds showed a similar diversity in contrast to that of the hypersaline Salt Pond (five phylotypes), where the diversity within cyanobacterial mats was reduced. Using the comparison of identified phylotypes with existing Antarctic sequence data, it was possible to gain further insight into the different levels of distribution of phylotypes identified in the investigated cyanobacterial mat communities of McMurdo Ice Shelf.     

Ground predator abundance affects prey removal in highbush blueberry (<Emphasis Type="BoldItalic">Vaccinium corymbosum</Emphasis>) fields and can be altered by aisle ground covers

Habitat management to conserve natural enemies has increased biological control of insect pests in various cropping systems [Annu. Rev. Entomol. 45: 175–201, 2000]. We wanted to determine if insect predation in highbush blueberry, Vaccinium corymbosum L. (Ericales: Ericaceae), is influenced by manipulation of edaphic arthropod community and whether management of ground cover in aisles between blueberry rows enhances this community. The first question was studied in blueberry plots bounded by trenches permitting selective movement into plots (ingress) or out of plots (egress), as well as unbounded control plots. We observed a significant effect of boundary type on the arthropod communities relative abundance as measured with pitfall traps, with relative abundance highest in ingress plots, intermediate in control plots and lowest in egress plots. Effects of ground arthropod abundance on predation rates were assessed with onion fly, Delia antiqua (Meigen) (Diptera: Anthomyiidae), pupae as sentinel prey. Pupa recovery was greatest in egress boundary plots, intermediate in control plots and lowest in ingress boundary plots. Regression analyses indicate pupal recovery rate decreased as a function of carabid abundance as well as the abundance of non-insect ground predators. To determine if ground cover management influenced natural enemy abundance, aisles were clean cultivated or planted with three ground covers (clover, ryegrass, or buckwheat). Increasing ground cover had a significant effect on the relative abundance of Harpalus pensylvanicus De Geer (Coleoptera: Carabidae). In addition to conserving natural enemies for control of blueberry insect pests, we discuss additional benefits of ground covers that may increase their utility for blueberry production.     

Identification of substrates of human protein-tyrosine phosphatase PTPN22

Stimulation of mature T cells activates a downstream signaling cascade involving temporally and spatially regulated phosphorylation and dephosphorylation events mediated by protein-tyrosine kinases and phosphatases, respectively. PTPN22 (Lyp), a non-receptor protein-tyrosine phosphatase, is expressed exclusively in cells of hematopoietic origin, notably in T cells where it represses signaling through the T cell receptor. We used substrate trapping coupled with mass spectrometry-based peptide identification in an unbiased approach to identify physiological substrates of PTPN22. Several potential substrates were identified in lysates from pervanadate-stimulated Jurkat cells using PTPN22-D195A/C227S, an optimized substrate trap mutant of PTPN22. These included three novel PTPN22 substrates (Vav, CD3epsilon, and valosin containing protein) and two known substrates of PEP, the mouse homolog of PTPN22 (Lck and Zap70). T cell antigen receptor (TCR) zeta was also identified as a potential substrate in Jurkat lysates by direct immunoblotting. In vitro experiments with purified recombinant proteins demonstrated that PTPN22-D195A/C227S interacted directly with activated Lck, Zap70, and TCRzeta, confirming the initial substrate trap results. Native PTPN22 dephosphorylated Lck and Zap70 at their activating tyrosine residues Tyr-394 and Tyr-493, respectively, but not at the regulatory tyrosines Tyr-505 (Lck) or Tyr-319 (Zap70). Native PTPN22 also dephosphorylated TCRzeta in vitro and in cells, and its substrate trap variant co-immunoprecipitated with TCRzeta when both were coexpressed in 293T cells, establishing TCRzeta as a direct substrate of PTPN22.     

A protein dynamics study of photosystem II: the effects of protein conformation on reaction center function

Molecular dynamics simulations have been performed to study photosystem II structure and function. Structural information obtained from simulations was combined with ab initio computations of chromophore excited states. In contrast to calculations based on the x-ray structure, the molecular-dynamics-based calculations accurately predicted the experimental absorbance spectrum. In addition, our calculations correctly assigned the energy levels of reaction-center (RC) chromophores, as well as the lowest-energy antenna chlorophyll. The primary and secondary quinone electron acceptors, Q_A and Q_B, exhibited independent changes in position over the duration of the simulation. Q_B fluctuated between two binding sites similar to the proximal and distal sites previously observed in light- and dark-adapted RC from purple bacteria. Kinetic models were used to characterize the relative influence of chromophore geometry, site energies, and electron transport rates on RC efficiency. The fluctuating energy levels of antenna chromophores had a larger impact on quantum yield than did their relative positions. Variations in electron transport rates had the most significant effect and were sufficient to explain the experimentally observed multi-component decay of excitation in photosystem II. The implications of our results are discussed in the context of competing evolutionary selection pressures for RC structure and function.     

Do Current Standards of Practice in Canada Measure What is Relevant to Human Exposure at Contaminated Sites? II: Oral Bioaccessibility of Contaminants in Soil

Human health risk estimates for sites with contaminated soils are often based on the assumption that the outdoor soil sieved to < 250 μm is a reasonable surrogate for predicting exposures via incidental soil ingestion. In vitro bioaccessibility tests are also increasingly used to “improve” ingestion exposure predictions of contaminants at different sites. However, when considered in terms of factors that influence desorption of contaminants from particles and uptake into humans, available studies indicate that current “standards of practice” with respect to assays of oral bioaccessibility have a number of significant shortcomings, at least in Canada. These shortcomings are discussed and various factors that influence the assessment of bioaccessibility of contaminants in soils are examined. We finish with proposing some minimum data submission requirements to support the application and relevance of bioaccessibility assays at contaminated sites.     

The effects of angiotensin II on the coupled microstructural and biomechanical response of C57BL/6 mouse aorta

RationaleAbdominal aortic aneurysm (AAA) is a complex disease that leads to a localized dilation of the infrarenal aorta, the rupture of which is associated with significant morbidity and mortality. Animal models of AAA can be used to study how changes in the microstructural and biomechanical behavior of aortic tissues develop as disease progresses in these animals. We chose here to investigate the effect of angiotensin II (AngII) in C57BL/6 mice as a first step towards understanding how such changes occur in the established ApoE^?/? AngII infused mouse model of AAA.ObjectiveThe objective of this study was to utilize a recently developed device in our laboratory to determine how the microstructural and biomechanical properties of AngII-infused C57BL/6 wildtype mouse aorta change following 14 days of AngII infusion.MethodsC57BL/6 wildtype mice were infused with either saline or AngII for 14 day. Aortas were excised and tested using a device capable of simultaneously characterizing the biaxial mechanical response and load-dependent (unfixed, unfrozen) extracellular matrix organization of mouse aorta (using multiphoton microscopy). Peak strains and stiffness values were compared across experimental groups, and both datasets were fit to a Fung-type constitutive model. The mean mode and full width at half maximum (FWHM) of fiber histograms from two photon microscopy were quantified in order to assess the preferred fiber distribution and degree of fiber splay, respectively.ResultsThe axial stiffness of all mouse aorta was found to be an order of magnitude larger than the circumferential stiffness. The aortic diameter was found to be significantly increased for the AngII infused mice as compared to saline infused control (p=0.026). Aneurysm, defined as a percent increase in maximum diameter of 30% (defined with respect to saline control), was found in 3 of the 6 AngII infused mice. These three mice displayed adventitial collagen that lacked characteristic fiber crimp. The biomechanical response in the AngII infused mice showed significantly reduced circumferential compliance. We also noticed that the ability of the adventitial collagen fibers in AngII infused mice to disperse in reaction to circumferential loading was suppressed.ConclusionsCollagen remodeling is present following 14 days of AngII infusion in C57BL/6 mice. Aneurysmal development occurred in 50% of our AngII infused mice, and these dilatations were accompanied with adventitial collagen remodeling and decreased circumferential compliance.