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Balaton is the largest shallow lake in Central Europe. It is one of the few lakes where eutrophication processes have been successfully reversed. The creation of a wetland area on the lower part of the main inflow river played a major role in the re-oligotrophication processes. After several decades of operation and multiple transformations, an attempt was made to explore the microbial community of the water reservoir and its relationship with algal groups and environmental parameters. In the main inflow river, floods had the greatest effect on the microbial community composition, while in the open water areas of the wetland system, the algae production that develops due to external nutrient load was the main driver of the bacterial community. In the high-macrophyte-covered areas, the decomposition processes of the dying algae biomass were the most decisive. Finally, in the large open water areas of Lake Balaton, the external and internal nutrient loads together determined the algal production and thus the bacterial community composition. [ABSTRACT FROM AUTHOR]

Little is known about how various substances from living and decomposing aquatic macrophytes affect the horizontal patterns of planktonic bacterial communities. Study sites were located within Lake Kolon, which is a freshwater marsh and can be characterised by open-water sites and small ponds with different macrovegetation (Phragmites australis, Nymphea alba and Utricularia vulgaris). Our aim was to reveal the impact of these macrophytes on the composition of the planktonic microbial communities using comparative analysis of environmental parameters, microscopy and pyrosequencing data. Bacterial 16S rRNA gene sequences were dominated by members of phyla Proteobacteria (36%-72%), Bacteroidetes (12%-33%) and Actinobacteria (5%-26%), but in the anoxic sample the ratio of Chlorobi (54%) was also remarkable. In the phytoplankton community, Cryptomonas sp., Dinobryon divergens, Euglena acus and chrysoflagellates had the highest proportion. Despite the similarities in most of the measured environmental parameters, the inner ponds had different bacterial and algal communities, suggesting that the presence and quality of macrophytes directly and indirectly controlled the composition of microbial plankton. [ABSTRACT FROM AUTHOR]

Aerobic anoxygenic phototrophs (AAPs) are a group of photoheterotrophic bacteria common in natural waters. Here, AAP abundance and contribution to total bacterial abundance and biomass were investigated to test whether the trophic status of a lake or content of coloured dissolved organic matter (CDOM) play a role in determining AAP distribution and abundance in shallow inland lakes, with special focus on hypertrophic and polyhumic waters. Twenty-six different shallow lakes in Hungary were monitored. AAP abundance and biomass were determined by epifluorescence microscopy. The lakes exhibit a broad range of CDOM (2–7000 mg Pt L−1) and phytoplankton biomass (2–1200 μg L−1 chlorophyll a concentration). Very high AAP abundance (up to 3 × 107 cells mL−1) was observed in polyhumic and hypertrophic shallow lakes. AAP abundance was influenced by phytoplankton biomass and CDOM content, and these effects were interrelated. As determined, 40 μg L−1 chlorophyll a and 52 mg Pt L−1 CDOM are threshold levels above which these effects have a synergistic relationship. Hence, the observed high AAP abundance in some soda pans is a consequence of combined hypertrophy and high CDOM content. AAP contribution was influenced by total suspended solids (TSS) content: the success of AAP cells could be explained by high TSS levels, which might be explained by the decrease of their selective grazing control. [ABSTRACT FROM AUTHOR]