In this presentation we present results from several chytrid infection experiments using bloom forming cyanobacteria as hosts. Two potentially toxic cyanobacteria were used, isolated together with their chytrid parasites, Planktothrix rubescens and Dolichospermum spec. For P.rubescens we performed a full-factorial experiment to study how temperature and light interact to affect the dynamics of host and chytrid parasite. We used a dynamic host-parasite model to explore how temperature and light affect long term dynamics. Model exploration indicates that increasing temperature and light shifts equilibrium outcomes from P. rubescens persisting alone to stable coexistence and then to limit cycles. The results shed new light on the specific habitat of P. rubescens in the metalimnion of deep lakes. For Dolichospermum we used a newly isolated and described chytrid, which specializes on infecting heterocysts of the cyanobacterial host only. Chytrid infection resulted in a nearly 70-fold decrease in the heterocysts ability to fix nitrogen. Our results indicate that chytrid infection strongly decreased host growth, but only when nitrogen in the medium was absent, forcing the cyanobacterium to rely on nitrogen fixation from its - infected -  heterocysts. The results will be discussed in light of their interest for two different fields in lake ecology, host x parasite interactions and harmful cyanobacterial blooms.

Primary Presenter: Bastiaan Ibelings, University of Geneva (bastiaan.ibelings@unige.ch)

Authors:

Mridul Thomas, University of Geneva  (mridul.thomas@unige.ch)

Joren Wierenga, University of Geneva  (joren90@gmail.com)

Xujian Xu, University of Geneva  (Xujian.Xu@etu.unige.ch)

Ravi Ranjan, Alfred-Wegener-Institute, Helmholtz-Centre for Polar and Marine Research  (ravi.ranjan@hifmb.de)

Silke Van den Wyngaert, University of Turku  (silke@uglylab.eu)

Hans-Peter Grossart, IGB Berlin  (hanspeter.grossart@igb-berlin.de)