title: Facultative diazotrophy increases Cylindrospermopsis raciborskii competitiveness under fluctuating nitrogen availability.
abstract: Relative fitness of three bloom-forming and potentially toxic cyanobacteria from the subtropical St. John's River, Florida was investigated under a range of nutrient conditions, during a bloom dominated by Cylindrospermopsis raciborskii. Nitrogen (N) was the primary nutrient limiting phytoplankton primary productivity and biomass. Phytoplankton biomass was also enhanced by phosphorus (P) added either alone or jointly with N, suggesting different components of the phytoplankton experienced distinct nutrient limitations. Based on quantitative PCR, the diazotrophic cyanobacteria Anabaena sp. and C. raciborskii were responsible for the primary production response to P additions, while the nondiazotrophic Microcystis aeruginosa appeared to benefit from N released from the diazotrophs. Cylindrospermopsis raciborskii maintained high net growth rates under diazotrophic and nondiazotrophic conditions, while Anabaena sp. growth was significantly reduced under DIN enrichment. C. raciborskii appears to be a generalist with regard to N source, a lifestyle traditionally not considered a viable ecological strategy among diazotrophs. Using facultative diazotrophy, C. raciborskii gains a growth advantage under fluctuating DIN conditions, such as systems that are under the influence of anthropogenic N loading events. The described niche differentiation may be a key factor explaining the recent global expansion of C. raciborskii.
authors: Ocean Sciences Department, University of California Santa Cruz, Santa Cruz, CA, USA. pmoisander@umassd.edu
authors: Pia H
authors: PH
authors: Moisander
authors: Lou Anne
authors: LA
authors: Cheshire
authors: Jeremy
authors: J
authors: Braddy
authors: Elizabeth S
authors: ES
authors: Calandrino
authors: Melissa
authors: M
authors: Hoffman
authors: Michael F
authors: MF
authors: Piehler
authors: Hans W
authors: HW
authors: Paerl
mesh_terms: D017033:Anabaena / Q000254:growth & development / Q000502:physiology; D018533:Biomass; D000458:Cyanobacteria / Q000254:growth & development; D046891:Cylindrospermopsis / Q000502:physiology*; D005431:Florida; D056265:Microbial Interactions / Q000187:drug effects*; D046931:Microcystis / Q000254:growth & development / Q000378:metabolism; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D009586:Nitrogen Fixation / Q000187:drug effects*; D010758:Phosphorus / Q000032:analysis; D010839:Phytoplankton / Q000254:growth & development; D045483:Rivers / Q000737:chemistry / Q000382:microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000378:metabolism
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus; D009584:Nitrogen