Cell wall surface layer (S-layer) promotes colony formation in Microcystis : comparison of S-layer characteristics betwe
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CYANOBACTERIAL BLOOMS AND WATER ECOLOGICAL RESTORATION
Cell wall surface layer (S-layer) promotes colony formation in Microcystis: comparison of S-layer characteristics between colonial and unicellular forms of Microcystis and function conformation Yao Zu 1 & Sujuan Hong 1 & Chongxin Xu 1,2 & Weiwei Li 1 & Siyu Chen 1 & Jianhong Li 1 Received: 29 September 2019 / Accepted: 26 February 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Colony is a key to Microcystis becoming a dominant population and forming blooms. To find the mechanism of colony formation, we investigated cell wall structures of colonial and unicellular strains. Results showed that colonial strains had significant surface layer protein (S-layer) on the surface of cells than unicellular strains by transmission electron microscopy. Western blot showed colonial strains had more S-layer than the unicellular strains. When the S-layer gene (GenBank accession number CAO89090.1) of Microcystis aeruginosa PCC7806 was expressed in Synechocystis sp. PCC6803, PCC6803 aggregated into colonial morphology. The results indicated that the S-layer could promote colony formation in Microcystis. Based on the Slayer sequences of PCC6803 and PCC7806, nine S-layer genes in other Microcystis strains were screened from the GenBank. Sequence comparing showed that the S-layers conserved regions were all located in N-terminal. The S-layers contain repeats-intoxin (RTX) sequences with Ca2+-binding site, and their amino acid composition, hydrophobicity, isoelectric point, etc. were consistent with the characteristics of RTX-type S-layer in bacteria. Keywords S-layer . Colony . Unicellular . Microcystis . Synechocystis sp. . PCC6803 . Cell wall
Introduction With increase of water eutrophication and greenhouse effect, Microcystis blooms occur more and more worldwide, which bring about serious threats to water ecosystem and drinking water (Paerl and Huisman 2008; Steffen et al. 2017). A lot of studies have confirmed that higher water temperature in summer and autumn, plenty nitrogen and phosphorus nutrition, and suitable hydrological conditions were the necessary conditions for Microcystis blooms (Jacinavicius et al. 2018; Paerl 2009; Paerl et al. 2014; Yamamoto et al. 2002). In addition, colony aggregated from several hundreds of cells was also a key for Microcystis Responsible editor: Vitor Manuel Oliveira Vasconcelos * Jianhong Li [email protected]; [email protected] 1
School of Life Sciences, Nanjing Normal University, Nanjing 210046, China
2
Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China
population becoming dominant (Xiao et al. 2018). Some ecological advantages of Microcystis were strongly related to their colony morphology. The formation of large colonies could effectively prevent cells from viral, bacterial, zooplankton grazing attack, ultraviolet radiation, desiccation, and the other potential negative environmental factors. Meanwhile, colony was more beneficial to photosynthesis,
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