Mechanisms of dominance: coexistence of picocyanobacterial genotypes in a freshwater ecosystem

Abstract

The autotrophic picoplankton of the pelagic zone of the mesotrophic Lake Constance is dominated by phycoerythrin-rich unicellular cyanobacteria phylogenetically related to the marine Synechococcus and Prochlorococcus cluster. In Lake Constance, the abundance of picocyanobacteria shows a recurrent pattern of seasonal variations. Evidence of diverse subpopulations was obtained by electron-microscopic examination of natural water samples and isolated strains that unveiled different surface structures of picocyanobacteria. Further evidence was obtained by DNA analysis of 26 clonal isolates representing 12 different genotypes. Variations in light and nutrient supply revealed distinct abilities of the genetically different strains to cope with these stress situations. Furthermore, cultured heterotrophic nanoflagellates exhibited differential feeding preferences for certain Synechococcus strains. The findings imply that growth and loss rates of the natural cyanobacterial community may be influenced by its genetic composition. Phylogenetic analyses of isolated strains indicated that the physiological diversification of pelagic Synechococcus spp. has occurred during a recent adaptive radiation. An example for genetic mechanisms underlying physiological diversification is indicated by mobile DNA elements found in a Synechocystis strain also isolated from the pelagic zone of Lake Constance. The observations suggest that dominance of Synechococcus spp. was achieved by evolutionary adaptation and coexistence of numerous genotypes generating a physiologically highly diversified population.

Spring phytoplankton blooms in Xiangxi Bay of Three-Gorges Reservoir: spatiotemporal dynamics across sharp nutrient gradients

“…In the upstream region dominated by Chlorophyta, an obvious depletion of nitrogen was also observed, with the lowest DIN concentration of 4.28 mM at S13 on 28 April. This phenomenon indicates that Chlorophyta can grow faster and have a higher affinity for nutrients than other phytoplankton groups under low nitrogen conditions (Graneli and Moreira 1990;Postius and Ernst 1999).…”

Picocyanobacterial community structure and space-time dynamics in the subalpine Lake Maggiore (N. Italy)

“…Abiotic forcing also plays a role in driving Pcy dynamics. Changing physical and chemical variables in temperate lakes seem to support the coexistence of multiple Pcy genotypes (Postius, and Ernst 1999), resulting in a succession of Pcy subpopulations throughout the year. This pattern has been found in Lake Constance and suggests seasonal changes in Pcy community composition (Ernst et al 2000).…”

Assessing the dynamics and ecology of marine picophytoplankton: The importance of the eukaryotic component

“…Grazer size selectivity in field populations has been suggested previously (Dolan and Simek 1999;Worden and Binder 2003). Potentially, several ecotypes are represented within one flow cytometric population, and within populations, ecotype-specific grazing might occur (see Postius and Ernst 1999), or physiological constraints might render different cell sizes. It is unlikely that the observed cell size differences are related to differences in the proportion of larger replicating cells versus smaller divided cells given the sampling time (early morning).…”