A snapshot on prokaryotic diversity of the Solimões River basin (Amazon, Brazil).

The Amazon region has the largest hydrographic basin on the planet and is well known for its huge biodiversity of plants and animals. However, there is a lack of studies on aquatic microbial biodiversity in the Solimões River, one of its main water courses. To investigate the microbial biodiversity of this region, we performed 16S rRNA gene clone libraries from Solimões River and adjacent rivers and lakes. Our question was which microorganisms inhabit the different types of aquatic environments in this part of the basin, and how diversity varies among these environments (rivers and lakes). The microbial diversity generating 13 clone libraries of the bacterial 16S rRNA gene and 5 libraries of the archaeal 16S rRNA gene was assessed. Diversity measured by several alpha diversity indices (ACE, Chao, Shannon and Simpson) revealed significant differences in diversity indices between lake and river samples. The site with higher microbial diversity was in the Solimões River (4S), downstream the confluence with Purus River. The most common bacterial taxon was the cosmopolitan Polynucleobacter genus, widely observed in all samples. The phylum Thaumarchaeota was the prevailing archaeal taxon. Our results provide the first insight into the microbial diversity of the world's largest river basin.

Castor bean (Ricinus communis L.) as a potential environmental bioindicator.

Biomonitoring of air quality using living organisms is a very interesting approach to environmental impact assessment. Organisms with a vast distribution, such as plants, are widely used for these purposes. The castor bean (Ricinus communis L.) is an oleaginous plant that can potentially be used as a bioindicator plant owing to its rapid growth and large leaves, which have a wide surface area of contact with the air and the pollutants therein. This study investigated the the bioindicator potential of the castor bean by performing several tests. We observed statistically significant differences in the concentrations of chlorophyll a and b in the leaves of plants in polluted areas compared to that in the control group plants, which were located in a pollution-free area. Leaves of plants in the former group had higher peroxidase activity and showed a greater buffering ability than those of plants in the control group. The pKa values obtained via buffering capacity tests, revealed the presence of aminoazobenzene (an industrial dye) in leaves of R. communis. Genotoxicity was evaluated through the comet assay technique and revealed that other than some differences in DNA fragmentation, there is no statistically significant difference in this parameter between places analyzed. Our data indicate that R. communis can be a highly useful biological indicator. Further, we hypothesized that the castor bean can be a potential candidate for phytoremediation owing its physiological buffering capacity when exposed to substantial pollution.