Phase Transitions by an Abundant Protein in the Anammox Extracellular Matrix Mediate Cell-to-Cell Aggregation and Biofilm Formation

被引:9
|
作者
Seviour, Thomas [1 ]
Wong, Lan Li [1 ]
Lu, Yang [1 ]
Mugunthan, Sudarsan [1 ]
Yang, Qiaohui [2 ]
Segaran, Uma Shankari Do Chanda [1 ]
Bessarab, Irina [3 ]
Liebl, David [2 ]
Williams, Rohan B. H. [3 ]
Law, Yingyu [1 ]
Kjelleberg, Staffan [1 ,4 ,5 ]
机构
[1] Nanyang Technol Univ, Singapore Ctr Environm Life Sci Engn, Singapore, Singapore
[2] ASTAR, Microscopy Platform, Res Support Ctr, Singapore, Singapore
[3] Natl Univ Singapore, Singapore Ctr Environm Life Sci Engn, Singapore, Singapore
[4] Nanyang Technol Univ, Sch Biol Sci, Singapore, Singapore
[5] Univ New South Wales, Sch Biol Earth & Environm Sci, Sydney, NSW, Australia
来源
MBIO | 2020年 / 11卷 / 05期
基金
新加坡国家研究基金会;
关键词
anammox; aggregation; biofilm; droplets; extracellular matrix; phase transitions; surface proteins; BACTERIA; DISORDER; REACTOR;
D O I
10.1128/mBio.02052-20
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
This 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 beta-strands, and circular dichroism conducted on the isolated surface protein indicated that beta-strands are the dominant higher-order structure. The isolated protein was stained positively by the beta-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.
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页码:1 / 14
页数:14
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