title: Grazing-induced Synechococcus microcolony formation: experimental insights from two freshwater phylotypes.
abstract: Freshwater cyanobacteria of the genus Synechococcus are ubiquitous and organized either as single cells of diverse morphology or as microcolonies of different size. We studied the formation of microcolonies induced by the mixotrophic nanoflagellate Poterioochromonas sp. grazing on two Synechococcus strains belonging to phylotypes with different content of phycobiliproteins (PE: phycoerythrin-rich cells, L.Albano Group A; PC: phycocyanin-rich cells, MW101C3 Group I). The quantitative variations in cell abundance, morphological and physiological conditions were assessed on short-term incubations in semi-continuous cultures, single culture (PE, PC) and co-culture (PE+PC), with and without predators, by flow cytometry, and PhytoPAM. Under grazing pressure, we observed that (i) the abundance of PE single cells decreased over time with a concomitant formation of PE microcolonies; (ii) in PC single cultures, no significant variation in single cells was found and microcolonies did not form; (iii) both PE and PC formed monoclonal microcolonies in co-culture; (iv) PC cells increased the photosynthetic efficiency of the PSII (higher Fv/Fm) in co-culture. In the aftermath of microcolony formation as a predation-induced adaptation, our findings indicated a different response of Synechococcus phylotypes potentially co-existing in natural environment and the importance of their interaction.
authors.affiliation: Institute of Ecosystem Study, CNR-ISE, 28922 Verbania, Italy c.callieri@ise.cnr.it.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Callieri
authors.affiliation: Water Research Institute, CNR, Monterotondo, 00015 Rome, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Amalfitano
authors.affiliation: Institute of Ecosystem Study, CNR-ISE, 28922 Verbania, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Corno
authors.affiliation: Institute of Ecosystem Study, CNR-ISE, 28922 Verbania, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bertoni
mesh_terms: D002450:Cell Communication / Q000502:physiology*; D018920:Coculture Techniques; D005434:Flow Cytometry; D005618:Fresh Water / Q000382:microbiology; D010798:Phycocyanin / Q000378:metabolism; D010799:Phycoerythrin / Q000378:metabolism; D058009:Stramenopiles / Q000378:metabolism*; D046940:Synechococcus / Q000145:classification / Q000254:growth & development*; D014871:Water Microbiology
chemical_list: D010798:Phycocyanin; D010799:Phycoerythrin
keywords: Synechococcus phylotypes; microcolony formation; nanoflagellate grazing