Colony formation in the cyanobacterium Microcystis

Abstract

Morphological evolution from a unicellular to multicellular state provides greater opportunities for organisms to attain larger and more complex living forms. As the most common freshwater cyanobacterial genus, Microcystis is a unicellular microorganism, with high phenotypic plasticity, which forms colonies and blooms in lakes and reservoirs worldwide. We conducted a systematic review of field studies from the 1990s to 2017 where Microcystis was dominant. Microcystis was detected as the dominant genus in waterbodies from temperate to subtropical and tropical zones. Unicellular Microcystis spp. can be induced to form colonies by adjusting biotic and abiotic factors in laboratory. Colony formation by cell division has been induced by zooplankton filtrate, high Pb concentration, the presence of another cyanobacterium (Cylindrospermopsis raciborskii), heterotrophic bacteria, and by low temperature and light intensity. Colony formation by cell adhesion can be induced by zooplankton grazing, high Ca concentration, and microcystins. We hypothesise that single cells of all Microcystis morphospecies initially form colonies with a similar morphology to those found in the early spring. These colonies gradually change their morphology to that of M. ichthyoblabe, M. wesenbergii and M. aeruginosa with changing environmental conditions. Colony formation provides Microcystis with many ecological advantages, including adaption to varying light, sustained growth under poor nutrient supply, protection from chemical stressors and protection from grazing. These benefits represent passive tactics responding to environmental stress. Microcystis colonies form at the cost of decreased specific growth rates compared with a unicellular habit. Large colony size allows Microcystis to attain rapid floating velocities (maximum recorded for a single colony, ∼ 10.08 m h ) that enable them to develop and maintain a large biomass near the surface of eutrophic lakes, where they may shade and inhibit the growth of less-buoyant species in deeper layers. Over time, accompanying species may fail to maintain viable populations, allowing Microcystis to dominate. Microcystis blooms can be controlled by artificial mixing. Microcystis colonies and non-buoyant phytoplankton will be exposed to identical light conditions if they are evenly distributed over the water column. In that case, green algae and diatoms, which generally have a higher growth rate than Microcystis, will be more successful. Under such mixing conditions, other phytoplankton taxa could recover and the dominance of Microcystis would be reduced. This review advances our understanding of the factors and mechanisms affecting Microcystis colony formation and size in the field and laboratory through synthesis of current knowledge. The main transition pathways of morphological changes in Microcystis provide an example of the phenotypic plasticity of organisms during morphological evolution from a unicellular to multicellular state. We emphasise that the mechanisms and factors influencing competiti...

Morphological and Molecular Identification of Microcystin-Producing Cyanobacteria in Nine Shallow Bulgarian Water Bodies

“…All the results obtained in this study support the idea of rich intrageneric diversity with many transitions in the colonial morphology in the genus Microcystis. This is in accordance with the earlier accent on the taxonomic problems in LM identification of Microcystis caused by the variability of colonies with overlapping of the limits usually accepted for a particular morphospecies [37,38,51], as well as with the recent hypothesis that all Microcystis morphospecies are may be different morphotypes of just one genetically consistent species and their phenotypic plasticity is caused by environmental variables [8]. Considering also the earlier works on M. aaeruginosa, M. smithii, M. novacekii, and M. wesenbergii, based on 16S rRNA, or 16S rRNA-23S rRNA ITS and cpcBA-IGB regions which suggested monophyletic identity, or demonstrated lack of differences among morphospecies or showed their intermixed phylogenetic positions [50,[52][53][54], we support the opinion that taxonomic revision of Microcystis is needed.…”

“…They belonged to 30 genera from four orders (Chroococcales, Synechococcales, Oscillatoriales, and Nostocales). The highest number of cyanoprokaryotes was found in the coastal lakes Vaya (43) and Durankulak (22), followed by the coastal reservoirs Mandra (9), Poroy (8), Aheloy (3), and inland reservoir Sinyata Reka (2) and coastal lake Uzungeren (1). Cyanoprokaryotes were not found in the coastal lakes Shabla and Ezerets.…”

“…However, it is widely known that the traditional LM identification of some bloom causative species remains problematic because of the unresolved taxonomy of certain cyanoprokaryote genera. The phenotypic flexibility of some standard diagnostic features in the taxonomy of cyanoprokaryotes-including the shape and structure of colonies, presence/absence of gas vesicles, akinetes, or heterocytes [5][6][7][8]-has promoted the parallel use of both morphological and molecular phylogenetic data in a common polyphasic approach [9][10][11]. This approach includes different molecular techniques and is increasingly employed for the analysis of environmental samples (e.g., [12][13][14][15][16][17][18][19]).…”

Comparative phylogeography of two free‐living cosmopolitan cyanobacteria: Insights on biogeographic and latitudinal distribution

“…Specific traits of these two species are also involved in their ecological success, such as buoyancy provided by gas vesicles, which allows them to access optimum light and nutrient conditions in the water column; ability to release toxins; formation of akinetes in R. raciborskii and tolerance to a wide range of light intensities. Also, colony formation in M. aeruginosa provides many ecological advantages, including faster floating velocity and protection from chemicals and grazing (Padisák et al, ; Rzymski & Poniedziałek, ; Xiao, Li, & Reynolds, ). Interestingly, R. raciborskii has also been implicated in inducing colony formation in Microcystis due to the production of allelochemicals (Mello, Soares, Roland, & Lürling, ), suggesting a positive correlation between the adaptive advantages of the two species.…”

Effect of Zinc on Microcystis aeruginosa UTEX LB 2385 and Its Toxin Production

“…Future experiments should concentrate on the dynamics of aggregation formation as it relates to intracellular molecular profile, in response to increasing ZnCl 2 concentrations. Aggregation of many Microcystis species is thought to contribute to possible natural bloom formation, and subsequent protection from environmental factors such as heavy metals [63]. M. aeruginosa were shown able to survive in low concentrations of variable heavy metal compounds, and Microcystis blooms showed a capacity to bioaccumulate and sequester heavy metal compounds within historically eutrophic lakes [7,10,58].…”