Do Ectomycorrhizal Trees Select Ectomycorrhizal Fungi That Enhance Phosphorus Uptake under Nitrogen Enrichment?

Globally, forests are impacted by atmospheric nitrogen (N) deposition, affecting their structure and functioning above and below ground. All trees form mutualistic root symbioses with mycorrhizal fungi. Of the two kinds of mycorrhizal symbioses of trees, the ectomycorrhizal (EcM) symbiosis is much more sensitive to N enrichment than the arbuscular mycorrhizal (AM) symbiosis. Due to increasing N deposition, significant declines in the richness and abundance of EcM fungal species and shifts in community composition and functional traits have been recorded. Under increasing N deposition, ectomycorrhizal forests usually show enhanced foliar mass fractions of N, reduced foliar mass fractions of phosphorus (P), and, consequently, an increasing imbalance in the foliar N:P stoichiometry, ultimately impacting tree performance. The question has been raised of whether, under conditions of high N deposition, EcM trees can select EcM fungi that are both tolerant to high N availability and efficient in the acquisition of P, which could to some extent mitigate the negative impact of N deposition on nutrient balances. Here we evaluate the literature for mechanisms through which certain EcM fungi could increase P acquisition under increased N loading. We find very little evidence that under N enrichment, EcM fungi that have on average higher P efficiency might be selected and thereby prevent or delay tree N:P imbalances. However, methodological issues in some of these studies make it imperative to treat this conclusion with caution. Considering the importance of avoiding tree N:P disbalances under N enrichment and the need to restore EcM forests that have suffered from long-term excess N loading, further research into this question is urgently required

The Prevalence and Incidence of Sexually Transmitted Infections in a Prospective Cohort of Injection Drug Users in Vancouver, British Columbia

BACKGROUND: While several studies have reported on sexual risk behaviours and the prevalence of sexually transmitted infections (STIs) among injection drug users (IDUs), there are fewer prospective studies that have been able to examine populations of IDUs with no history of STIs. Therefore, the authors examined prevalence, correlates and factors associated with time to first STI infection in a prospective cohort of IDUs in Vancouver, British Columbia

Predictors of Early Hospital Readmission in HIV-infected Patients with Pneumonia

OBJECTIVE: Although hospitalization patterns have been studied, little is known about hospital readmission among HIV-infected patients in the era of highly active antiretroviral therapy. We explored the risk factors for early readmission to a tertiary care inner-city hospital among HIV-infected patients with pneumonia in Vancouver, Canada. DESIGN: Case-control study. SETTING: Tertiary care, university-affiliated, inner-city hospital. PARTICIPANTS: All HIV-infected patients who were hospitalized with Pneumocystis carinii pneumonia (PCP) or bacterial pneumonia (BP) between January 1997 and December 2000. Case patients included those who had early readmissions, defined as being readmitted within 2 weeks of discharge (N = 131). Control patients were randomly selected HIV-infected patients admitted during the study period who were not readmitted within 2 weeks of discharge (N = 131), matched to the cases by proportion of PCP to BP. MEASUREMENTS: Sociodemographic, HIV risk category, and clinical data were compared using χ(2) test for categorical variables, and the Wilcoxon rank-sum test was used for continuous variables. Multivariable logistic regression was performed to determine the factors independently associated with early readmission. We also reviewed the medical records of 132 patients admitted to the HIV/AIDS ward during the study period and collected more detailed clinical data for a subanalysis. MAIN RESULTS: Patients were at significantly increased odds of early readmission if they left the hospital against medical advice (AMA) (adjusted odds ratio [OR], 4.26; 95% confidence interval [95% CI], 2.13 to 8.55), lived in the poorest urban neighborhood (OR, 2.03; 95% CI, 1.09 to 3.77), were hospitalized in summer season (May though October, OR, 2.36; 95% CI, 1.36 to 4.10), or had been admitted in the preceding 6 months (OR, 2.55; 95% CI, 1.46 to 4.47). Gender, age, history of AIDS-defining illness, and injection drug use status were not significantly associated with early readmission. CONCLUSIONS: Predictors of early readmission of HIV-infected patients with pneumonia included: leaving hospital AMA, living in the poorest urban neighborhood, being hospitalized in the preceding 6 months and during the summer months. Interventions involving social work may address some of the underlying reasons why these patients leave hospital AMA and should be further studied

Overexpression of NADH-dependent fumarate reductase improves d-xylose fermentation in recombinant Saccharomyces cerevisiae

Deviation from optimal levels and ratios of redox cofactors NAD(H) and NADP(H) is common when microbes are metabolically engineered. The resulting redox imbalance often reduces the rate of substrate utilization as well as biomass and product formation. An example is the metabolism of D-xylose by recombinant Saccharomyces cerevisiae strains expressing xylose reductase and xylitol dehydrogenase encoding genes from Scheffersomyces stipitis. This pathway requires both NADPH and NAD+. The effect of overexpressing the glycosomal NADH-dependent fumarate reductase (FRD) of Trypanosoma brucei in D-xylose-utilizing S. cerevisiae alone and together with an endogenous, cytosol directed NADH-kinase (POS5∆17) was studied as one possible solution to overcome this imbalance. Expression of FRD and FRD + POS5∆17 resulted in 60 and 23 % increase in ethanol yield, respectively, on D-xylose under anaerobic conditions. At the same time, xylitol yield decreased in the FRD strain suggesting an improvement in redox balance. We show that fumarate reductase of T. brucei can provide an important source of NAD+ in yeast under anaerobic conditions, and can be useful for metabolic engineering strategies where the redox cofactors need to be balanced. The effects of FRD and NADH-kinase on aerobic and anaerobic D-xylose and D-glucose metabolism are discussed