Resumo

Rivers and streams are important reservoirs of fresh water available for consumption. The increasing urbanization represents a threat to these ecosystems. The discharge of sewage alters the content of nutrients and may affect the composition of the microbial community. Our study aimed to investigate the microbial taxonomic diversity of an urban lotic environment. Samples of running water were collected in two sites of São Pedro stream: an upstream preserved and non-urbanized area, and a polluted urbanized area with sewage discharge. The metagenomic DNA was extracted using PowerMax Soil Kit, MoBio, and sequenced using 454 GS-FLX Titanium, Roche. The quality trimmed reads were compared against the NT and NR-NCBI databases using BLAST tools (cut-off:e-value≤1e-5). The results were visualized on MEGAN v4.0. Analysis using MG-RAST was also done (e-value cut-off:1e-5, min%Identity:60). To determine statistically significant differences between the two metagenomes, the STAMP package was used. Considering the annotated reads, both metagenomes were dominated by bacteria (99.2% and 96.3% on urbanized and non-urbanized metagenome respectively), and a smaller fraction from archaea (0.3% and 2.9%). The Proteobacteria was the most prevalent phylum on both metagenomes (77.1% and 70.6%), followed by Bacteroidetes (13.2%), Firmicutes (4.5%), Actinobacteria (3%), on the urbanized and Firmicutes (5%), Acidobacteria (5%), Verrucomicrobia (4.5%), on the non-urbanized. The overrepresented genera and species in the non-urbanized metagenome were microbes ubiquitous on soil and waters that are important on the maintenance of the environments. There was an enrichment of genera (Burkholderia, Escherichia, Shigella, Bacteroides, Salmonella, Acinetobacter, Vibrio, Yersinia) and species related to pathogenicity for humans on the urbanized metagenome. There were a higher number of sequences annotated for few specialized groups on this metagenome unlike the non-urbanized that had a more equitable distribution. Our results emphasize the selection pressure exercised by the excess of urban sewage discharged on the freshwater environments. There was a change on the structure of the microbial community imposed by the uncontrolled anthropic interference. We showed the scenario of a local stream that reflects the situation of aquatic ecosystems in Brazil. The detection of potentially pathogenic bacteria on these environments represents an important issue with public health consequences.