The Extracytoplasmic Domain of the Mycobacterium tuberculosis Ser/Thr Kinase PknB Binds Specific Muropeptides and Is Required for PknB Localization

The Mycobacterium tuberculosis Ser/Thr kinase PknB has been implicated in the regulation of cell growth and morphology in this organism. The extracytoplasmic domain of this membrane protein comprises four penicillin binding protein and Ser/Thr kinase associated (PASTA) domains, which are predicted to bind stem peptides of peptidoglycan. Using a comprehensive library of synthetic muropeptides, we demonstrate that the extracytoplasmic domain of PknB binds muropeptides in a manner dependent on the presence of specific amino acids at the second and third positions of the stem peptide, and on the presence of the sugar moiety N-acetylmuramic acid linked to the peptide. We further show that PknB localizes strongly to the mid-cell and also to the cell poles, and that the extracytoplasmic domain is required for PknB localization. In contrast to strong growth stimulation by conditioned medium, we observe no growth stimulation of M. tuberculosis by a synthetic muropeptide with high affinity for the PknB PASTAs. We do find a moderate effect of a high affinity peptide on resuscitation of dormant cells. While the PASTA domains of PknB may play a role in stimulating growth by binding exogenous peptidoglycan fragments, our data indicate that a major function of these domains is for proper PknB localization, likely through binding of peptidoglycan fragments produced locally at the mid-cell and the cell poles. These data suggest a model in which PknB is targeted to the sites of peptidoglycan turnover to regulate cell growth and cell division

Water Quality of Streams and Springs around a Municipal Landfill Surrounded by Intense Agricultural Activities in a Tropical Environment

In Cameroon waste disposal by open dumping and landfilling are the most practised options. The siting, operation and after-care of landfills remain a challenging task. In this study we assessed water quality of stream, spring and leachate samples around/from the Mussaka landfill through physicochemical, heavy metal, microbial, phytoplankton, and benthic algae analyses. HCO3-, NH4-, NO3- concentrations are all above permissible limits EPA and WHO standards for freshwater systems. Concentrations of Ca2+ and Mg2+ in stream samples were far below standards but far greater (>480 mg/L) in spring and leachate samples. Nickel, lead and cadmium concentrations were above required standards. Contamination factors of all stream samples (CF<3) imply low to moderate contamination but pollution load index for spring sample (PLI>1) imply the spring is polluted. Generally, the obtained concentrations of most of these parameters were far higher for leachate than water samples. Total coliform counts ranged from 3.5 MPN/100mL to 1.1x103 MPN/100 mL. Five E. coli species were detected in all samples in counts ranging from 3.0x102 to 1.0x103CFU/mL. Thirty phytoplankton species belonging to 5 divisions were identified with Bacillariophyta (19 species) having the highest abundance and Euglenophyta (1 species) with least. Ten genera were identified as pollution indicator species. Results of this study justify the assertion that if upgrading options are not sought for the Mussaka landfill, it will become a major source of pollution of aquatic and soil ecosystems within the landfill area and downstream

Historical drought patterns over Canada and their teleconnections with large-scale climate signals

Drought is a recurring extreme climate event and among the most costly natural disasters in the world. This is particularly true over Canada, where drought is both a frequent and damaging phenomenon with impacts on regional water resources, agriculture, industry, aquatic ecosystems, and health. However, nationwide drought assessments are currently lacking and impacted by limited ground-based observations. This study provides a comprehensive analysis of historical droughts over the whole of Canada, including the role of large-scale teleconnections. Drought events are characterized by the Standardized Precipitation Evapotranspiration Index (SPEI) over various temporal scales (1, 3, 6, and 12 consecutive months, 6 months from April to September, and 12 months from October to September) applied to different gridded monthly data sets for the period 1950–2013. The Mann–Kendall test, rotated empirical orthogonal function, continuous wavelet transform, and wavelet coherence analyses are used, respectively, to investigate the trend, spatio-temporal patterns, periodicity, and teleconnectivity of drought events. Results indicate that southern (northern) parts of the country experienced significant trends towards drier (wetter) conditions although substantial variability exists. Two spatially well-defined regions with different temporal evolution of droughts were identified – the Canadian Prairies and northern central Canada. The analyses also revealed the presence of a dominant periodicity of between 8 and 32 months in the Prairie region and between 8 and 40 months in the northern central region. These cycles of low-frequency variability are found to be associated principally with the Pacific–North American (PNA) and Multivariate El Niño/Southern Oscillation Index (MEI) relative to other considered large-scale climate indices. This study is the first of its kind to identify dominant periodicities in drought variability over the whole of Canada in terms of when the drought events occur, their duration, and how often they occur