CHANGES IN THE MORPHOLOGY AND POLYSACCHARIDE CONTENT OF <i>MICROCYSTIS AERUGINOSA</i> (CYANOBACTERIA) DURING FLAGELLATE GRAZING<sup>1</sup>

Kong

Ann. Limnol. - Int. J. Lim.

et al. 2009

Self Cite

-Colonial Microcystis aeruginosa were obtained when the unicellular algae were exposed to flagellate Ochromonas sp. filtrate. To investigate the benefit of this morphological change, flagellates were added into cultures of unicellular and colonial M. aeruginosa, respectively. The clearance rates of flagellates on algae were markedly decreased when they were cultivated with induced colonial M. aeruginosa. This result indicated that colony formation in M. aeruginosa was a predator-induced defense, which could reduce predation risk from flagellate. The increased content of soluble extracellular polysaccharide (sEPS) and bound extracellular polysaccharide (bEPS) may play an important role in adhering M. aeruginosa cells together to form colonies. The decrease of WPS II and the increase of sinking rates of induced colonial M. aeruginosa showed that the costs of grazed-induced colony formation in M. aeruginosa may reflect in the photosystem II efficiency, and in the sinking rates.

Section: Discussionsupporting

confidence: 82%

Benefits and costs of the grazer-induced colony formation inMicrocystis aeruginosa

Kong

Ann. Limnol. - Int. J. Lim.

et al. 2009

Self Cite

“…Several laboratory experiments have reported that the formation of colonies or aggregates might be a response by Microcystis to various environmental stresses. Burkert et al (2001) and Yang et al (2008) showed induction of colonies in axenic M. aeruginosa in the presence of the predator Ochromonas. Sedmak & Eleršek (2005) reported that unicellular M. aeruginosa strains aggregated in the presence of commercial microcystins.…”

Section: Cell Aggregationmentioning

confidence: 99%

“…Previous laboratory studies (Shen & Song, 2007;Wu et al, 2007) indicated that unicellular and colonial Microcystis display different physiological characteristics, especially in terms of their responses to environmental stress. Formation of colonies or aggregates could be induced by flagellate grazing (Burkert et al, 2001;Yang et al, 2008) and by extracellular microcystins (Sedmak & Eleršek, 2005).…”

Section: Introductionmentioning

confidence: 99%

Morphological and physiological changes in Microcystis aeruginosa as a result of interactions with heterotrophic bacteria

et al. 2011

SUMMARY1. To reveal the role of aquatic heterotrophic bacteria in the process of development of Microcystis blooms in natural waters, we cocultured unicellular Microcystis aeruginosa with a natural Microcystis-associated heterotrophic bacterial community. 2. Unicellular M. aeruginosa at different initial cell densities aggregated into colonies in the presence of heterotrophic bacteria, while axenic Microcystis continued to grow as single cells. The specific growth rate, the chl a content, the maximum electron transport rate (ETR max ) and the synthesis and secretion of extracellular polysaccharide (EPS) were higher in non-axenic M. aeruginosa than in axenic M. aeruginosa after cell aggregation, whereas axenic and non-axenic M. aeruginosa displayed the same physiological characteristic before aggregation. 3. Heterotrophic bacterial community composition was analysed by PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. The biomass of heterotrophic bacteria strongly increased in the coinoculated cultures, but the DGGE banding patterns in coinoculated cultures were distinctly dissimilar to those in control cultures with only heterotrophic bacteria. Sequencing of DGGE bands suggested that Porphyrobacter, Flavobacteriaceae and one uncultured bacterium could be specialist bacteria responsible for the aggregation of M. aeruginosa. 4. The production of EPS in non-axenic M. aeruginosa created microenvironments that probably served to link both cyanobacterial cells and their associated bacterial cells into mutually beneficial colonies. Microcystis colony formation facilitates the maintenance of high biomass for a long time, and the growth of heterotrophic bacteria was enhanced by EPS secretion from M. aeruginosa. 5. The results from our study suggest that natural heterotrophic bacterial communities have a role in the development of Microcystis blooms in natural waters. The mechanisms behind the changes of the bacterial community and interaction between cyanobacteria and heterotrophic bacteria need further investigations.

Ann. Limnol. - Int. J. Lim.

“…Bloom-forming cyanobacteria generally exist as massive or filamentous colonies. Among the many features associated with large colonial forms of cyanobacteria include quick vertical migration (Kromkamp and Walsby, 1990), effective uptake of phosphorus (Shen and Song, 2007), protection from ultraviolet radiation (Sommaruga et al, 2009) and invulnerability to grazers (Ghadouani et al, 2003;Yang et al, 2008). These features are closely related to the ecological advantages of bloom-forming cyanobacteria over unicellular species in water ecosystems.…”

Section: Introductionmentioning

confidence: 99%

Variation in the growth ofMicrocystis aeruginosadepending on colony size and position in colonies

Yamamoto

Shiah

2010

-Growth of colonial Microcystis aeruginosa was investigated by performing an incubation experiment. Colonies of M. aeruginosa were separated based on size (colony diameter <100 mm, 100-200 mm and > 200 mm) by filtration. Additionally, the cells around the surface of the colonies were separated from those inside the colonies by short-term ultrasonic treatment followed by filtration. Experimental results indicate that M. aeruginosa grew continuously throughout a 35-day incubation period in a nutrient-rich medium at specific growth rates between 0.045 and 0.310 d x1 . On day 14, larger colonies exhibited insignificantly higher specific growth rates. However, on day 35, the specific growth rates of colonies with diameters less than 100 mm insignificantly exceeded those of larger colonies. Internal cells of the colonies tended to grow faster than peripheral cells. Furthermore, the specific growth rates of the cells that comprised colonies with diameters of below 200 mm exceeded those of peripheral cells. These results suggest a potential growth strategy of M. aeruginosa in maintaining a high growth rate, eventually leading to the dominance of large colonies, which have notable ecological advantages over smaller ones.