Surface-layer protein is a public-good matrix exopolymer for microbial community organisation in environmental anammox biofilms

• Main Authors: Wong, Lan Li, Lu, Yang, Ho, James Chin Shing, Mugunthan, Sudarsan, Law, Yingyu, Conway, Patricia, Kjelleberg, Staffan, Seviour, Thomas
• Other Authors: School of Biological Sciences
• Format: Article
• Language: English
• Published: 2023
• Subjects: Engineering::Environmental engineering; Science::Biological sciences; Wastewater Treatment; Nitrogen Removal
• Online Access: https://hdl.handle.net/10356/165788
• Institution: Nanyang Technological University

Extracellular polymeric substances (EPS) are core biofilm components, yet how they mediate interactions within and contribute to the structuring of biofilms is largely unknown, particularly for non-culturable microbial communities that predominate in environmental habitats. To address this knowledge gap, we explored the role of EPS in an anaerobic ammonium oxidation (anammox) biofilm. An extracellular glycoprotein, BROSI_A1236, from an anammox bacterium, formed envelopes around the anammox cells, supporting its identification as a surface (S-) layer protein. However, the S-layer protein also appeared at the edge of the biofilm, in close proximity to the polysaccharide-coated filamentous Chloroflexi bacteria but distal to the anammox bacterial cells. The Chloroflexi bacteria assembled into a cross-linked network at the edge of the granules and surrounding anammox cell clusters, with the S-layer protein occupying the space around the Chloroflexi. The anammox S-layer protein was also abundant at junctions between Chloroflexi cells. Thus, the S-layer protein is likely transported through the matrix as an EPS and also acts as an adhesive to facilitate the assembly of filamentous Chloroflexi into a three-dimensional biofilm lattice. The spatial distribution of the S-layer protein within the mixed species biofilm suggests that it is a "public-good" EPS, which facilitates the assembly of other bacteria into a framework for the benefit of the biofilm community, and enables key syntrophic relationships, including anammox.