Impact of pollution on the microbial diversity of a tropical river in an urbanized region of northeastern Brazil.

Rivers are important ecosystems that are integrated into biogeochemical cycles and constitute an essential resource for numerous human uses. However, the assessment of the biological diversity and composition of microbial communities found in rivers remains incomplete, partly due to methodological constraints which are only recently being resolved with the advent of next generation sequencing (NGS) techniques. Using 454-pyrosequencing of the 16S gene, the present study analyzed the microbial diversity of the planktonic and sediment populations in a tropical river in northeastern Brazil that is exposed to severe pollution. Six water and six sediment samples were analysed. The dominant bacterial phyla in both sediment and water were the Proteobacteria, followed by Bacteroidetes and Actinobacteria in the water column and by Chloroflexi and Acidobacteria in the sediment. Biological diversity appeared to be greatly decreased by environmental pollution, whereas the microbial community structure was variable across the analyzed transect. Moreover, a narrow relationship between industrial and urban sources of contamination and the bacterial genera detected at these sites has been observed. A variety of potentially pathogenic bacteria was detected, including Klebsiella, Treponema, Faecalibacterium and Enterococcus, indicating that the river might pose a substantial risk to public health. [Int Microbiol 20(1): 11-24 (2017)].

Effects of a type I antifreeze protein (AFP) on the melting of frozen AFP and AFP+solute aqueous solutions studied by NMR microimaging experiment.

The effects of a type I AFP on the bulk melting of frozen AFP solutions and frozen AFP+solute solutions were studied through an NMR microimaging experiment. The solutes studied include sodium chloride and glucose and the amino acids alanine, threonine, arginine, and aspartic acid. We found that the AFP is able to induce the bulk melting of the frozen AFP solutions at temperatures lower than 0 °C and can also keep the ice melted at higher temperatures in the AFP+solute solutions than those in the corresponding solute solutions. The latter shows that the ice phases were in super-heated states in the frozen AFP+solute solutions. We have tried to understand the first experimental phenomenon via the recent theoretical prediction that type I AFP can induce the local melting of ice upon adsorption to ice surfaces. The latter experimental phenomenon was explained with the hypothesis that the adsorption of AFP to ice surfaces introduces a less hydrophilic water-AFP-ice interfacial region, which repels the ionic/hydrophilic solutes. Thus, this interfacial region formed an intermediate chemical potential layer between the water phase and the ice phase, which prevented the transfer of water from the ice phase to the water phase. We have also attempted to understand the significance of the observed melting phenomena to the survival of organisms that express AFPs over cold winters.