Cyanophage Propagation in the Freshwater Cyanobacterium Phormidium Is Constrained by Phosphorus Limitation and Enhanced by Elevated p CO2

Kai Cheng; Thijs Frenken; Corina P D Brussaard; Dedmer B Van de Waal

doi:10.3389/fmicb.2019.00617

Cyanophage Propagation in the Freshwater Cyanobacterium Phormidium Is Constrained by Phosphorus Limitation and Enhanced by Elevated p CO₂

Front Microbiol. 2019 Mar 29:10:617. doi: 10.3389/fmicb.2019.00617. eCollection 2019.

Authors

Kai Cheng^{1

2}, Thijs Frenken², Corina P D Brussaard³, Dedmer B Van de Waal²

Affiliations

¹ Hubei Key Laboratory of Ecological Restoration for River-Lakes and Algal Utilization, College of Resources and Environmental Engineering, Hubei University of Technology, Wuhan, China.
² Department of Aquatic Ecology, Netherlands Institute of Ecology, Wageningen, Netherlands.
³ Department of Marine Microbiology and Biogeochemistry, Royal Netherlands Institute for Sea Research and University of Utrecht, Texel, Netherlands.

Abstract

Intensification of human activities has led to changes in the availabilities of CO₂ and nutrients in freshwater ecosystems, which may greatly alter the physiological status of phytoplankton. Viruses require hosts for their reproduction and shifts in phytoplankton host physiology through global environmental change may thus affect viral infections as well. Various studies have investigated the impacts of single environmental factors on phytoplankton virus propagation, yet little is known about the impacts of multiple factors, particularly in freshwater systems. We therefore tested the combined effects of phosphorus limitation and elevated pCO₂ on the propagation of a cyanophage infecting a freshwater cyanobacterium. To this end, we cultured Phormidium in P-limited chemostats under ambient (400 μatm) and elevated (800 μatm) pCO₂ at growth rates of 0.6, 0.3, and 0.05 d^-1. Host C:P ratios generally increased with strengthened P-limitation and with elevated pCO₂. Upon host steady state conditions, virus growth characteristics were obtained in separate infection assays where hosts were infected by the double-stranded DNA cyanophage PP. Severe P-limitation (host growth 0.05 d^-1) led to a 85% decrease in cyanophage production rate and a 73% decrease in burst size compared to the 0.6 d^-1 grown P-limited cultures. Elevated pCO₂ induced a 96% increase in cyanophage production rate and a 57% increase in burst size, as well as an 85% shorter latent period as compared to ambient pCO₂ at the different host growth rates. In addition, elevated pCO₂ caused a decrease in the plaquing efficiency and an increase in the abortion percentage for the 0.05 d^-1 P-limited treatment, while the plaquing efficiency increased for the 0.6 d^-1 P-limited cultures. Together, our results demonstrate interactive effects of elevated pCO₂ and P-limitation on cyanophage propagation, and show that viral propagation is generally constrained by P-limitation but enhanced with elevated pCO₂. Our findings indicate that global change will likely have a severe impact on virus growth characteristics and thereby on the control of cyanobacterial hosts in freshwater ecosystems.

Keywords: EOP; abortive infection; adsorption; climate change; cyanobacterial virus; freshwater; one step growth curve; pathogen.