Analysis of the Microbial Community Along Three Sites of the Rio Grande by Denaturing Gradient Gel Electrophoresis

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Texas A&M International University


Analysis of the Microbial Community of Three Sites Along the Rio Grande by Denaturing Gradient Gel Electrophoresis (May 2014)

Rebeca Imelda Castro, B. A., Texas A & M International University;

Chair of Committee: Dr. Monica Mendez

In the last decades, the increase in population growth and differences in enforcement regulations on both sides of the Rio Grande may have affected the bacterial composition as a result of effluent discharges, industrial waste, raw sewage outfalls, and agricultural runoff. The purpose of this study was to compare structural differences in the microbial communities of the Rio Grande-Rio Bravo waters based on Denaturing Gradient Gel Electrophoresis (DGGE) analysis. Three sites were selected based on proximity to anthropogenic influences with the highest level to the lowest level of potential human impact (from the site furthest downstream to upstream) as follows: Site 1-Zacate Creek Area located downstream of the Zacate Waste Water Treatment Plant; Site 2-Bridge I, located upstream of the U.S.-Mexico International Bridge I; and Site 3- Jefferson Water Treatment Plant Intake located upstream of Site 2-Bridge I. In order to assess environmental factors potentially affecting the microbial composition at these sites, physiochemical parameters were determined such as: water temperature, conductivity, pH, depth, chlorophyll a, optical dissolved oxygen, total nitrogen and total phosphorous. The microbial community was analyzed using heterotrophic plate counts on R2A agar and by PCR amplification of the 16S rRNA gene followed by DGGE analysis. Although water quality parameters were similar, differences between the sites were noted for the microbial communities. Heterotrophic plate counts were significantly highest (p = 0.0006) at Site1-ZCA and the lowest at Site 3-JWTP. Based on DGGE analysis, similar trends were observed with the OTU richness which was highest for Site 1-ZCA (28 OTUs), which had six unique OTUs, and lowest for Site3-JWTP. Possible influences could be eutrophic conditions from a build-up of nutrients including dissolved organic matter, salts or other inorganic contaminants, most likely from sewage and waste water discharges nearest Sites 1 and 2. Results suggest that general water quality parameters may not be sufficient in determining potential anthropogenic impacts on the microbial community, and that other factors not assessed in this study could be impacting the bacterial richness and diversity of the Rio Grande.