Abstract
The aim of this study was to evaluate the co-occurrence of some frequent fecal indicator bacteria and cyanobacteria species at San Roque reservoir (SRr), highlighting the relationship between their variability and environmental factors. This study was carried out at SRr (31°22′ S, 64°27′ O) located west of the city of Cordoba, Argentina. Physico-chemical measurements and sampling for microbiological and nutrient determinations were done at three recreational sites, during seasons of major touristic activity (spring-summer), with the aim of identifying temporal patterns of microorganism variability. In addition, we carried out laboratory experiments with local isolated bacteria (Escherichia coli and Enterococcus spp.) and axenic Microcystis aeruginosa cultures to assess an association among these microorganisms and evaluate whether it was positive or negative. Our results showed an inverse relationship between cyanobacteria and thermotolerant coliform bacteria (TtC) at SRr, which was only observed when high cyanobacteria concentration occurred (≥3.4 × 104 to 1.2 × 106 cell.mL−1). Experimental results also showed this type of relationship: E. coli and Enterococcus spp. decreased their growth in the presence of M. aeruginosa. In addition, it was observed that the variability of main phytoplanktonic species and TtC at SRr was mainly explained by temporal patterns, that is, the seasonal changes and the hydrological year. In summary, our data indicated that cyanobacteria high abundance during bloom periods could be an inhibiting factor for bacteria growth at SRr. Moreover, we demonstrated that nutrients such us P and N are not the main factors determining the variability of studied microorganisms in this eutrophic reservoir, but other factors, such as climatic conditions (temperature and precipitations), have a major influence. This study would provide a more comprehensive view on the dynamics of microorganism populations with sanitary relevance in eutrophic reservoirs.
Highlights
The eutrophication of freshwater systems is a current problem commonly related to anthropogenic nutrient overloading (Smith and Schindler 2009; Lewis et al 2011; Moss et al 2011)
Our study proposed to evaluate the relationship between local bacteria able to be cultured and cyanobacteria species in a eutrophic reservoir, using different approaches: field sampling during natural blooms in freshwater and batch experiments on M. aeruginosa and local fecal indicator bacteria species isolated from local reservoirs
Spearman coefficients showed a significant negative correlation between thermotolerant coliform bacteria (TtC) and cyanobacteria species only during T1-T2, being E. coli significantly negative correlated with M. aeruginosa and Dolichospermum spp. (Table 1)
Summary
The eutrophication of freshwater systems is a current problem commonly related to anthropogenic nutrient overloading (Smith and Schindler 2009; Lewis et al 2011; Moss et al 2011). Warm water temperatures and high concentrations of nutrients could be promoting factors of E. coli survival and growth outside the host (Byappanahalli et al 2006; Whitman et al 2006) The occurrence of both cyanobacteria and bacteria species certainly affect recreational and domestic use of reservoir water and can impact negatively on diverse conditions of the system, for example, oxygen and light, nutrient cycling and food chain composition (Muylaert et al 2002; Karjalainen et al 2007; Wilhelm et al 2011). Health risk of cyanobacteria blooms could be enhanced by favoring the potential growth of bacteria, especially at reservoirs with recreational and drinking water use purposes
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