engleski

Bacterial diversity along a salinity gradinet in a saltwedge karstic estuary

Estuaries represent the mixing zone between freshwater introduced by rivers and the open sea. They are a ‘melting pot’ of environmental stressors, typified by extreme salinity variations and associated biological complexity and strong physical interactions. The Krka river estuary extends 25km into the heartland of the karstic Dalmatia. The estuary is relatively narrow but it enlarges in the Lake Prokljan and Šibenik Bay regions, respectively. The estuary is characterized by low terrigenous input due to karstic drainage area. The surface low salinity layer is separated form the high – salinity deeper layers by a very sharp, ~ 20cm tick halocline layer, and this interface is greatly enriched with dissolved and particulate organic matter and suspended matter and selectively with viable phytoplankton cells. The strucure and abundance of bacterial communities and the abundance of individual bacterial taxa have been examined in aquatic systems over the past 30 years. We investigated for the first time in the Krka estuary the diversity of bacterial communities using 454 pyrosequencing and CARD - FISH. Samples for bacterial community structure analysis were taken onboard on 25 February and 10 July 2013 at three stations in the estuary and one outside of the estuary (as a reference). Alphaprotobacteria dominated the water column during the investigated period. The second most abundant pyrotags in winter were the Chloroplast sequences and in summer Cyanobacteria. All other groups were distributed similarly in winter/summer period. Gammaproteobacteria differed in summer and winter samples. SAR86 sequences were the most dominant in winter and Litoricola sequences in summer. Actinobacteria differed significantly in summer (dominated by OCS155 group) and in winter (dominated by candidatus Aquilina). Bacterioidetes were the most heterogeneous group where Flavobacteria dominated in winter and NS4 and NS5 in summer. Using CARD FISH we were able to quantify the most dominant groups (Gammaproteobacteria, Actinobacteria, Betaproteobacteria, Cyanobacteria, SAR11 clade and Roseobacter). The number of bacteria varied from 75 x 104 cells/ml (AD3-45m-W) to 212 x 104 cells/ml (E3-0m-S). The innermost station was the least dominated by the SAR11 clade, Betaproteobacteria were detected in the surface samples. Our results demonstrated a strong influence of season on the bacterial community.

bacteria; saltwedge; karst; 454

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