Selfish bacteria utilize polysaccharides in freshwater lakes
Bacteria utilize polysaccharides trough three different mechanism: scavenging, sharing and selfish. To explore distribution of selfish uptake of polysaccharides among bacteria in freshwater environment, a detailed research was conducted in two natural karst oligotrophic and mesotrophic lakes. Two opposite lakes are located in Croatia, in continental region (Kozjak) influenced by continental climate, and in Mediterranean region (Crniševo) influenced by Mediterranean climate. Samples were taken in three different seasons, spring, summer and winter. Fluorescently labelled substrate incubations were performed with six different polysaccharides (arabinogalactan, chondroitin sulfate, fucoidan, laminarin, pullulan, and xylan). Taxonomic changes of the bacterial community were analyzed by sequencing the 16S rRNA gene. Fluorescence in situ hybridization was done to identify the bacteria involved in selfish uptake.  Mesotrophic lake (Crniševo) showed greater microbial diversity and ability for selfish uptake, especially during phytoplankton bloom, while oligotrophic lake (Kozjak) showed higher selfish activity during period of intense terrestrial influence. FISH staining combined with microbial diversity analysis revealed the selfish activity of phyla Bacteroidota, Planctomycetota, and Verrucomicrobiota, as well as class Gammaproteobacteria, with different genera active depending on lake, season and substrate.