Abstract
Compositional changes of the bacterioplankton assemblages in four high altitude middle Atlas lakes were monitored over a complete seasonal cycle using combinations of culture-dependent and molecular approaches. Viable bacterial numbers varied between seasons, with the lowest numbers recorded in the winter and the highest in the summer in all four lakes. Also, bacterial occurrences were found to be strongly correlated with water temperature in all the four sites, i.e., Lake Aoua (0.88), Ifreh (0.59), Hechlef (0.77) and Affourgagh (0.79) during the study period. Standard microbiological characterization of bacteria isolates from the lakes revealed majority (68%) to be Gram positive. Seasonal variations in the microbial assemblages among the lakes were also validated by restriction fragment length polymorphism (RFLP). Shifts in microbial assemblages, especially of the fecal indicator bacteria appeared to also be influenced by differences in the morphometric and watershed characteristics among the lakes. This study further reveals the need to employ combinations of methodological approaches, including taxonomic, physiological and molecular methods to adequately delineate and fully understand the ecology of microbial assemblages in extreme environments.
Highlights
Increasing recognition regarding the ecological importance of and contributions by autochthonous microbial assemblages in aquatic systems has significantly heightened the need to further examine and elucidate their community compositions, structures and dynamics [e.g. 1, 6,18,19,27]
A total of 44 bacterial isolates cultured from samples collected the four lakes were characterized based on combinations of their morphological, physiological and biochemical attributes
(viable bacterial count) and culture-independent molecular (i.e. PCR detection and restriction fragment length polymorphism (RFLP)) methods utilized in this study, both established the seasonal shifts in the bacterioplankton assemblages within the four high altitude lakes
Summary
Increasing recognition regarding the ecological importance of and contributions by autochthonous microbial assemblages in aquatic systems has significantly heightened the need to further examine and elucidate their community compositions, structures and dynamics [e.g. 1, 6,18,19,27]. Bacterial occurrences and compositional changes in microbial assemblages within extreme environments such as in high altitudes have attracted much attention in order to better understand the impacts of seasonal conditions on the occurrences and diversity of indigenous bacterial populations [1,9,21]. Some of these studies have revealed high compositional changes in the microbial community structures between seasons [e.g.,21], while others have documented such shifts between different habitats (i.e. snow, slush and the water body) in freshwater systems in extreme environments [e.g.,1]. Most of these past studies only based their reports on the elucidation of microbial assemblages within individual lakes, and to the best of our knowledge, very limited information currently exists on microbial occurrence and activities across multiple lakes located in high altitude environments [7].
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