The role of the heterocyte in the ecology of two bloom forming nitrogen fixing Cyanobacteria

YEMA, LILÉN; LITCHMAN, ELENA; DE TEZANOS PINTO, PAULA

Granada

Congreso; ASLO; 2015

ASLO

In nitrogenfixing cyanobacteria the trait of nitrogen fixation (heterocyte) usually favorsblooms in situations with low nitrogen, yet blooms can also occur at highnitrogen. We studied the role of the heterocyte in the ecology of two species(Dolichospermum flos ?aquae and Cylindrospermopsis raciborskii) which havecontrasting position of the heterocyte in its filaments. We exposedmonocultures to contrasting nitrogen (0 and 1000 µmol/L) and phosphorous (2 and15 µmol/L) concentrations, for 4 weeks. In both species nitrogen fixationoccurred (range 22-37 µmol/L d-1) only in the absence of nitrogen, coincidingwith high heterocyte density. D. flos aquae (heterocytes develop intercalary inthe filament) achieved high biomass regardless of nitrogen availability, yetfilaments were longer when heterocytes developed. C. raciborskii (heterocytesdevelop at the end of the filament) achieved little biomass when relying onfixation, and its filaments were extremely short. But, at nitrogen sufficiency,it achieved high biomass and long filaments; also heterocytes were expressed(but no fixation occurred). Heterocyte position may explain the contrastingecologies of D. flos aquae and C. raciborskii (biomass, filament length,heterocyte expression).