Enriched functional exoproteins and increased exopolysaccharides with altered molecular conformation mutually promoted indigenous microalgal-bacterial consortium biofilm growth under high light intensity

Indigenous microalgal-bacterial consortium (IMBC) biofilm technology holds great promise for wastewater treatment. However, the efficient start-up of IMBC biofilm system remains a technical challenge, partially impeding its large-scale application due to the unclear biofilm formation mechanism. In this study, high light intensity (HL) irradiation was firstly demonstrated as an effective strategy to promote IMBC biofilm development, as evidenced by the 498.3% higher biofilm formation ratio on average. Interaction energy between IMBC and carrier, exoproteins (PN) annotation and exopolysaccharides (PS) chain characteristics were investigated to reveal the potential mechanism. The decreased interfacial free energy (by 33.8%) and negative total interaction energies between IMBC and carriers in the HL group indicated enhanced microbial initial adhesion onto carriers. PN and PS were believed to mutually promote biofilm proliferation. Specifically, enriched PN with signal transduction potential and transmembrane transporter activity ensured efficient production of extracellular polymeric substances (EPS) for biofilm development. On one hand, PN annotated with binding capacities contributed to a tightly-interconnected EPS matrix. On the other hand, the increased PS with higher branding degree, height, and width (by 473%, 63.4%, and 28.9%, respectively) significantly enhanced the structural stability of biofilm landscape. These findings enrich our knowledge of the roles of EPS in IMBC biofilm growth, and are expected to promote the development of IMBC wastewater bioremediation technology.