ISPUB.COM The Internet Journal of Microbiology Volume 12 Number 1 1 of 12 Bacterial Diversity and Physicochemical Stratification of the Water Column during the Rainy Season in Las Cumbres Lake, Panama G Bruner, L Jimenez, Y Mendoza, B Chial, M de Chial Citation G Bruner, L Jimenez, Y Mendoza, B Chial, M de Chial. Bacterial Diversity and Physicochemical Stratification of the Water Column during the Rainy Season in Las Cumbres Lake, Panama. The Internet Journal of Microbiology. 2013 Volume 12 Number 1. Abstract Bacterial diversity was studied in Las Cumbres Lake, Panama City, in relation to the physicochemical variables of the lake during the rainy season. Water samples were taken at different depths, and physicochemical variables (temperature, dissolved oxygen, total solids, phosphate and nitrate concentrations) and a biological indicator of wastewater pollution, the total coliform count, were determined. To examine bacterial diversity, 16S rRNA clone libraries from each depth were analyzed. In total, 255 bacterial sequences were obtained and assigned to OTUs (operational taxonomic units) corresponding to a similarity threshold of 97% (0.03 cutoff). This resulted in 24 total OTU assignments from different phyla, such as Proteobacteria, Bacteriodetes, Verrucomicrobia, Actinobacteria and Chlorobi. Alpha (a) diversity was assessed by rarefaction curves. At three depths (0, 5 and 10 meters), this analysis demonstrated that the sampling effort was sufficient to represent the diversity of the communities. Beta (b) diversity was analyzed by means of a Venn diagram and revealed a large number of unique species at each depth. This study pioneers and establishes methods that can be used for similar studies in freshwater and marine environments in Panamá, and suggests that surveys of water quality should sample from deeper strata, in addition to surface waters. INTRODUCTION Physicochemical variations throughout a body of water such as a lake are dependent in part on microbial activities (Hohnk, 1962).Microbes are responsible for providing essential elements of life through biogeochemical cycling (Kirchman, 2008).Some essential processes that maintain life on earth and are performed by microbes are, among others, organic matter degradation, recycling of CO2, and nitrogen fixation from the atmosphere. Microorganisms also have a large impact on the distribution of organic and inorganic nutrients in the ocean because they efficiently and thoroughly penetrate both the water and sediment layers by virtue of by their high numbers (Surajit, et al., 2006). To this end, microbes possess extracellular catabolic enzymes that decompose various dissolved and particulate substrates, and the release of these nutrients makes life possible in an aquatic environment (Meyer-Reil 1994). Of equal importance, the biodiversity of the bacteria that participate in these processes is dependent upon environmental conditions such as the seasons of the year, wind fluctuations, geomorphology of the lake, and anthropogenic influences. Human activities in the form of household and industrial wastes and nutrient status alterations impact heavily upon aquatic ecosystems.Microbes respond readily to anthropogenic pollution, which is responsible for changes in microbial diversity and shifts in dominant phylotype representation (Kuznetzov, 1970, Matcher, et al., 2011). Determining physical and chemical factors, such as temperature, pH, and geography, that correlate with differences between diverse microbial communities will reveal how easily microbes tolerate different environmental changes and will increase our understanding of microbial ecology(Lozupone and Knight, 2007). Metagenomics, a culture-independent method to study bacterial biodiversity, gives more insights into true bacterial