Colicine Typing of Shigella sonnei

The colicine typing method of Shigella sonnei is described with experimental evidence supporting it as well as the manner of selection of eight indicator strains. The disparity of principle between this method and that of Abbott and Shannon's method is (1) selection of the indicators only from wild strains existing in this country, (2) employment of heart infusion broth for colicine production, (3) performance of the typing within 48 hours, and (4) determination of types and subtypes of test-strains by combining their colicinogenic activity against the indicators and their sensitivity to colicines produced by the indicators. A modification of the method is advocated which requires three days to extract colicine by cultivation and one day for sensitivity tests and which uses peptone as the sole nutriment in media. The efficiency of the technique of Abbott and Shannon, McGeachie and McCormick, and the authors' two methods was compared using the selected indicators. Only the technique of McGeachie and McCormick showed some discrepancies.     

The effects of water pollution on the phylogenetic community structure of aquatic plants in the East Tiaoxi River,China

1. Water pollution is one of the most serious aquatic environmental problems worldwide. In China, recent agricultural and industrial development has resulted in rapid changes in aquatic ecosystems. Here, we reveal the effects of water pollution on the phylogenetic community structure of aquatic macrophytes in the Tiaoxi River, China.
2. We placed a rectangular plot at 47 sites within the Tiaoxi River from the mouth of the river to 88.5 km upstream, in which we recorded species abundance and measured 22 physico-chemical variables. Bayesian phylogeny using the rbcL and matK gene sequences was employed to quantify phylogenetic α- and β-diversity, and test the phylogenetic signal in four growth forms: emergent, floating-leaved, free-floating, and submerged.
3. Within communities, water contamination and phytoplankton abundance decreased species richness and phylogenetic diversity, which resulted in phylogenetic clustering; species within communities were more closely related to each other than expected. Between communities, differences in geographical distance and phytoplankton abundance resulted in phylogenetic dissimilarity among plots. Aquatic macrophytes showed phylogenetic signals in which related species responded more similarly to disturbance.
4. Thus, the observed patterns could be explained by environmental filtering and suggested that water pollution by human activity has added more filters to the existing environmental filters that drive the species assembly of macrophyte communities.