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dc.contributor.authorSeviour, Thomasen_US
dc.contributor.authorWong, Lan Lien_US
dc.contributor.authorLu, Yangen_US
dc.contributor.authorMugunthan, Sudarsanen_US
dc.contributor.authorYang, Qiaohuien_US
dc.contributor.authorChanda Segaran, Uma Shankarien_US
dc.contributor.authorBessarab, Irinaen_US
dc.contributor.authorLiebl, Daviden_US
dc.contributor.authorWilliams, Rohan B. H.en_US
dc.contributor.authorLaw, Yingyuen_US
dc.contributor.authorKjelleberg, Staffanen_US
dc.identifier.citationSeviour, T., Wong, L. L., Lu, Y., Chanda Segaran, U. S., Bessarab, I., Liebl, D., . . . Kjelleberg, S. (2020). Phase transitions by an abundant protein in the anammox extracellular matrix mediate cell-to-cell aggregation and biofilm formation. mBio, 11(5), e02052-20-. doi:10.1128/mBio.02052-20en_US
dc.description.abstractThis study describes the first direct functional assignment of a highly abundant extracellular protein from a key environmental and biotechnological biofilm performing an anaerobic ammonium oxidation (anammox) process. Expression levels of Brosi_A1236, belonging to a class of proteins previously suggested to be cell surface associated, were in the top one percentile of all genes in the "Candidatus Brocadia sinica"-enriched biofilm. The Brosi_A1236 structure was computationally predicted to consist of immunoglobulin-like anti-parallel β-strands, and circular dichroism conducted on the isolated surface protein indicated that β-strands are the dominant higher-order structure. The isolated protein was stained positively by the β-sheet-specific stain thioflavin T, along with cell surface- and matrix-associated regions of the biofilm. The surface protein has a large unstructured content, including two highly disordered domains at its C terminus. The disordered domains bound to the substratum and thereby facilitated the adhesion of negatively charged latex microspheres, which were used as a proxy for cells. The disordered domains and isolated whole surface protein also underwent liquid-liquid phase separation to form liquid droplets in suspension. Liquid droplets of disordered protein wet the surfaces of microspheres and bacterial cells and facilitated their coalescence. Furthermore, the surface layer protein formed gels as well as ordered crystalline structures. These observations suggest that biophysical remodeling through phase transitions promotes aggregation and biofilm formation. Importance: By employing biophysical and liquid-liquid phase separation concepts, this study revealed how a highly abundant extracellular protein enhances the key environmental and industrial bioprocess of anaerobic ammonium oxidation (anammox). Extracellular proteins of environmental biofilms are understudied and poorly annotated in public databases. Understanding the function of extracellular proteins is also increasingly important for improving bioprocesses and resource recovery. Here, protein functions were assessed based on theoretical predictions of intrinsically disordered domains, known to promote adhesion and liquid-liquid phase separation, and available surface layer protein properties. A model is thus proposed to explain how the protein promotes aggregation and biofilm formation by extracellular matrix remodeling and phase transitions. This work provides a strong foundation for functional investigations of extracellular proteins involved in biofilm development.en_US
dc.description.sponsorshipMinistry of Education (MOE)en_US
dc.description.sponsorshipNanyang Technological Universityen_US
dc.description.sponsorshipNational Research Foundation (NRF)en_US
dc.description.sponsorshipNational University of Singapore (NUS), Temasek Laboratoriesen_US
dc.rights© 2020 Seviour et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.en_US
dc.subjectScience::Biological sciencesen_US
dc.titlePhase transitions by an abundant protein in the anammox extracellular matrix mediate cell-to-cell aggregation and biofilm formationen_US
dc.typeJournal Articleen
dc.contributor.schoolSchool of Biological Sciencesen_US
dc.contributor.researchSingapore Centre for Environmental Life Sciences and Engineeringen_US
dc.description.versionPublished versionen_US
dc.description.acknowledgementThis research was supported by the Singapore National Research Foundation under its Environment & Water Industry Research Programme and administered by PUB, project number 1301-IRIS-59. SCELSE is funded by Singapore’s Ministry of Education, National Research Federation, Nanyang Technological University (NTU), and National University of Singapore (NUS) and hosted by NTU in partnership with NUS.en_US
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