Casting a net: fibres produced by Microcystis sp. in field and laboratory populations

Abstract

Summary The reasons for the apparent dominance of the toxic cyanobacterium Microcystis sp., reflected by its massive blooms in many fresh water bodies, are poorly understood. We show that in addition to a large array of secondary metabolites, some of which are toxic to eukaryotes, Microcystis sp. secretes large amounts of fibrous exopolysaccharides that form extremely long fibres several millimetres in length. This phenomenon was detected in field and laboratory cultures of various Microcystis strains. In addition, we have identified and characterized three of the proteins associated with the fibres and the genes encoding them in Microcystis sp. PCC 7806 but were unable to completely delete them from its genome. Phylogenetic analysis of the most abundant one, designated IPF‐469, showed its presence only in cyanobacteria. Its closest relatives were detected in Synechocystis sp. PCC 6803 and in Cyanothece sp. strains; in the latter the genomic organization of the IPF‐469 was highly conserved. IPF‐469 and the other two proteins identified here, a haloperoxidase and a haemolysin‐type calcium‐binding protein, may be part of the fibres secretion pathway. The biological role of the fibres in Microcystis sp. is discussed.

UVB Radiation as a Potential Selective Factor Favoring Microcystin Producing Bloom Forming Cyanobacteria

“…Not only protective pigments, the colony dimension itself can also confer UV screening due to self-shading of several layers of cells [29]. The formation of massive cell envelopes or slime layers embedding the colonies are frequently exopolysaccharide fibril structures associated with proteins [30]. Such a matrix surrounding mature colonies can also serve as an effective UV filter.…”

Drag increase and drag reduction found in phytoplankton and bacterial cultures in laminar flow: Are cell surfaces and EPS producing rheological thickening and a Lotus-leaf Effect?

“…Many phytoplankton and bacteria, including those we investigated, also have nm-or mm irregularities. Skeletonema bears long fibres (Castellví, 1969;Sarno et al, 2005), the freshwater cyanobacterium Microcystis can have fibres several mm long (Harel et al, 2012), Escherichia coli has multiple long flagella, and the dinoflagellates Karenia and Alexandrium have indentations, flagella and, at a smaller length scale, secrete mucous fibrils (Honsell and Talarico, 2004). Furthermore, a variable but sometimes large proportion (∼90%) of the dissolved organic carbon secreted by phytoplankton in situ has been found to be hydrophobic, and to adsorb at surfaces Ćosović, 1992, 1996).…”

Calcium promotes formation of large colonies of the cyanobacterium Microcystis by enhancing cell-adhesion

“…Since Ca 2+ is essential in cyanobacterial photosynthesis (Becker and Brand, 1982), some uptake by cells is to be expected. In addition, Microcystis secretes large amounts of fibrous exopolysaccharides in which a calcium-binding protein is involved (Harel et al, 2012). In this exopolysaccharide environment calcium binding takes place (Jansson and Northen, 2010), calcium complexation has been well-documented (e.g.…”