Hydrobiologia 506–509: 721–728, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. 721 Bacterial activities in the sediment of Lake Velencei, Hungary Andrea K. Borsodi 1 , P´ eter Vlad´ ar 1 , G´ abor Cech 1 , G´ abor Gedeon 2 , B´ ank Beszteri 1 , Adrienn Micsinai 1 , M´ aria N. Resk´ on´ e 3 & K´ aroly M´ arialigeti 1 1 Department of Microbiology, Eötvös Lor´ and University, H-1117 Budapest, P´ azm´ any P. s´ et´ any 1/C, Hungary E-mail: bandrea@ludens.elte.hu 2 Department of Genetics, Eötvös Lor´ and University, H-1117 Budapest, P´ azm´ any P. s´ et´ any 1/C, Hungary 3 Central Transdanubian Inspectorate for Environmental Protection, H-8000 Sz´ ekesfeh´ erv´ ar, Hossz´ us´ etat´ er 1, Hungary Key words: soda lake sediment, alkaliphilic Bacillus, clostridia, sulphate-reducing bacteria, BIOLOG, 16S rDNA Abstract Lake Velencei (Hungary) is one of the westernmost shallow soda lakes, extending from Eastern Europe to the Carpatian basin. The spatial and temporal distribution of the sediment microbiota, the metabolic potential of bacterial communities and the species composition of the genera Bacillus and Clostridium, as well as sulphate- reducing bacteria (SRB) were investigated regarding the close interactions between the lake sediment and the overlaying water column, the special water chemical parameters, and the extensive reed coverage of the lake. Aerobic microbial activities were tested with community-level physiological profiling (CLPP) using BIOLOG microplates. The quantification of the anaerobic fermentative and sulphate-reducing bacteria was done by the MPN (Most Probable Number) method. The cultivation of bacteria adapted to the special physico-chemical char- acteristics of the lake was carried out employing selective media. Multivariate analysis of CLPP data indicated that the microbial communities of the sediment separated from that of the water and showed seasonal variations of the utilised carbon sources. The results of the MPN demonstrated that the counts of the fermentative and sulphate- reducing bacteria in the reed rhizosphere were about one order higher than in the sediment. Among the isolated bacterial strains, a large number were characterised as facultative or obligate alkaliphilic and also moderately halophilic. The partial sequencing of 16S rDNA of the selected representatives resulted in species of aerobic bacteria, such as Bacillus pseudofirmus, B. halmapalus, B. cohnii, B. (Marinibacillus) marinus, and anaerobes, such as Clostridium putrificum – sporogenes, C. scatologenes, C. bifermentans, Desulfotomaculum guttoideum, Desulfovibrio alcoholivorans, and Desulfovibrio burkinensis. Introduction In freshwater lake sediments the microbiota, consist- ing of physiologically diverse aerobic and anaerobic microorganisms, play an important role in the de- composition and mineralization of organic materials (Wellsbury et al., 1996; Spring et al., 2000; Nixdorf & Jander, 2003). The microbial metabolism in the water-sediment interface is usually not influenced con- siderably by the absence of oxygen. Nevertheless in the lower, reduced sediment layers, which are rich in decaying plant material, the carbon and electron flow is derived mainly from the decomposition of cellulose and can involve various trophic groups of anaerobic microorganisms (e.g. biopolymer-degrading primary fermenting bacteria, syntrophic fermenting bacteria, methanogens, and/or sulphate-reducing bacteria) (Le- shine & Canale-Parola, 1983; Hines et al., 1999; Brune et al., 2000; Holmer et al., 2001). Aquatic mac- rophytes (e.g. Phragmites, Typha) deeply influence the sediment species composition and metabolic activities through their rhizosphere effect (Andrews & Harris, 2000; Brune et al., 2000; Yang & Crowley, 2000; Ostendorp et al., 2003). The widely distributed soda lakes are usually char- acterized by high microbial productivity and dense