engleski

Structure of microbial community in respect to hypoxia in meromictic lake.

Bacterial abundance, biomass, volume and bacterial activity were studied in water column samples collected from small meromictic saline lake during the holomictic period (Rogoznica Lake, Croatia). Special attention was paid to the impact of water column hypoxia on investigated parameters. The abundances of heterotrophic (HNF) and autotrophic (ANF) flagellates were also investigated in order to determine their relevance in regulation of bacterial population density and activity. Bacterial abundances did not exhibit considerable changes in respect to water column hypoxia ranging from 3.10 to 3.73 x 106 cells ml-1. During hypoxia bacterial biomass ranged from 9.14 to 19.64 mg C ml-1 and was two times greater than the values recorded after hypoxic event. Bacterial cell specific volume ranged from 0.009 to 0.296 m3 and was always higher during hypoxia. Low-DNA bacteria dominated the bacterial community in hypoxic environment accounting from 76 to 80% of total number of bacteria. The abundances of HNF and ANF decreased 5-7 times in the presence of low O2 concentrations implying their strong relation to the oxygen concentrations in water.The presences of elemental sulfur as the predominant reduced sulfur species in both environments imply the importance of microbiological sulfide reoxydation.

heterotrophic bacteria; heterotrophic flagellates; autotrophic flagellates; nonloricate ciliates; Rogoznica Lake

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