Abstract
The study investigated species composition and polysaccharides, proteins, and eDNA content in EPS fractions (soluble, Sol-EPS; loosely bound, LB-EPS; tightly bound, TB-EPS) in nitrifying aerobic granules from reactor operated at a high load of nitrogen 0.5 kg TKN/(m3 × day). In the study, polysaccharides predominated in Sol-EPS, whereas proteins were the main component of bound EPS. eDNA was only detectable in TB-EPS. In Sol-EPS, eDNA originating from Pseudomonales predominated; species belonging to Pseudomonales produce glue-like polysaccharides that enable surface colonization. In all EPS fractions, high abundance of Acinetobacter sp. was noted. In TB-EPS, Thauera sp. was present in high abundance (25.6%) that produce polymers ensuring compact granule structure and that participate in many key metabolic processes for nitrogen conversions in wastewater treatment plants such as heterotrophic nitrification or denitrification. The study indicates that each EPS fraction in aerobic granules represents micro-environment facilitating the growth of species that produce a component of EPS with function essential for surrounding cells.
Highlights
Extracellular polymeric substances (EPS) are important components of microbial communities and are responsible for the formation of flocs, biofilm, and granules
The first step to identify the origin of eDNA in different fractions of EPS was PCR-DGGE
The bacterial communities of soluble EPS (Sol-EPS) and loosely bound EPS (LB-EPS), and of tightly bound EPS (TB-EPS) and total DNA were grouped into two distinct branches, indicating that composition of eDNA in TB-EPS was mostly determined by the composition of the total bacterial community in aerobic granules
Summary
Extracellular polymeric substances (EPS) are important components of microbial communities and are responsible for the formation of flocs, biofilm, and granules. The EPS matrix is a three-dimensional structure in which cells conduct extracellular activities and interactions that cannot be accomplished efficiently by free-living cells. The resistance of microorganisms in the EPS matrix is higher in mature, well-developed biofilms than in young biofilms that are more prone to treatment by biochemical methods (Michel et al 2011). Sol-EPS are present in bulk liquid and are responsible for the first step of biofilm formation, which is connected with surface conditioning. LB-EPS permit microcolonies to connect together and form flocs. TB-EPS are present on the cell walls of microorganisms and help cells to adhere to each other and form microcolonies (Nielsen and Jahn 1999)
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