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.

中文翻译：

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关于圣罗克水库（阿根廷）蓝藻与粪便指示菌负相关的首次报告：环境因素的影响

摘要 本研究的目的是评估圣罗克水库 (SRr) 中一些常见的粪便指示菌和蓝藻物种的共存情况，强调它们的变异性与环境因素之间的关系。这项研究是在位于阿根廷科尔多瓦市西部的 SRr (31°22' S, 64°27' O) 进行的。在主要旅游活动季节（春夏）期间，在三个娱乐场所进行了用于微生物和营养测定的物理化学测量和采样，目的是确定微生物变异的时间模式。此外，我们对当地分离的细菌（大肠杆菌和肠球菌属）进行了实验室实验。) 和无菌铜绿微囊藻培养物以评估这些微生物之间的关联并评估它是阳性还是阴性。我们的结果显示蓝藻和耐热大肠菌群 (TtC) 在 SRr 之间呈负相关，这仅在发生高蓝藻浓度（≥3.4 × 104 至 1.2 × 106 cell.mL−1）时观察到。实验结果也显示了这种关系：大肠杆菌和肠球菌属。在铜绿假单胞菌存在下降低了它们的生长。此外，观察到SRr主要浮游植物物种和TtC的变异性主要由时间模式解释，即季节变化和水文年份。总之，我们的数据表明，开花期间蓝藻的高丰度可能是 SRr 细菌生长的抑制因素。此外，我们证明了 P 和 N 等营养物质不是决定该富营养化水库中所研究微生物变异性的主要因素，但气候条件（温度和降水）等其他因素具有重大影响。这项研究将为富营养化水库中与卫生相关的微生物种群动态提供更全面的观点。