Characteristics and bacterial community dynamics during extracellular polymeric substance (EPS) degradation of...

Extracellular polymeric substances (EPSs), which composed of different organic components, play an important role in the formation of mucilaginous cyanobacterial bloom. However, how the phylogeny of microbial community coupling with the degradation of EPS matrixes remains unclear. A better understanding of the dynamic process not only give insight into the carbon cycling in the phycosphere, but also provide a new approach for controlling the cyanobacteria bloom. In this study, fractionated EPSs were prepared as a carbon source to enrich different particle size microorganisms. Changes of organic components in EPSs and microbial communities in the degradation process were investigated using Fluorescence excitation and emission matrix (EEM) and Illumina sequencing. The results showed that it is the change of organic components in the degradation process that causes the microbial community to follow a certain succession law. Size-fractionated microorganisms exhibited different hydrolytic activities when interacting with macromolecules, but they did not present different phylogenetic compositions. The changes of humic-like C1 and tryptophan-like C3 in EPSs were significantly correlated to the variations of microbial community composition and diversity. Tightly-bound EPSs (TB-EPSs) contained more low molecular single carbon compounds and were more easily utilized by more diverse microorganisms. Betaproteobacteria, Firmicute, Alphaproteobacteria, Sphingobacteria and Actinobacter were significantly correlated with the changes of organic maters through the humification process. Meanwhile, loosely-bound EPSs (LB-EPSs), which composed of more macromolecules, were more affiliated to a functional organized microbial community. When Gammaproteobacteria and Betaproteobacteria were involved in LB-EPS degradation as indicators, the polysaccharide structures changed dramatically. And the content of some small molecules was briefly increased during the degradation process. Therefore, in order to prevent algal bloom from reducing cellular aggregation by decreasing viscous EPSs, specialized microbial communities should be considered in the phycosphere.