Viral-phytoplankton interactions: Isolation, characterization

Viral-phytoplankton interactions: Isolation, characterization and ecology of viruses infecting the
diatom Pseudo-nitzschia
Michael Carlson1*, Benjamin Johnson1, Gabrielle Rocap1
School of Oceanography, University of Washington, Seattle, WA
Presenting author
Viruses are important regulators of phytoplankton communities, contributing to bloom
termination and preventing transfer of fixed carbon to higher trophic levels. Although diatoms
are one the most important marine primary producers, only a few diatom-infecting viruses have
been characterized. The cosmopolitan diatom genus Pseudo-nitzschia is most noted for the
ability to produce domoic acid, a neurotoxin that can reach ecologically dangerous levels during
large blooms. Toxic blooms of Pseudo-nitzschia are common in coastal Washington waters but
in 2005 was a toxic bloom of Pseudo-nitzschia detected inside Puget Sound. Preliminary data
suggest the viral size fraction of water collected during this bloom event is lethal to some
cultures of Pseudo-nitzschia. We hypothesize that there may be several viruses that can infect
Pseudo-nitzschia, ranging from single stranded RNA viruses to double stranded DNA viruses
from the Phycodnaviridae. Isolation and characterization of the putative Pseudo-nitzschia
virus(es) is currently underway. Exponentially growing Pseudo-nitzschia cultures are challenged
with environmental samples and monitored for potential lytic events via both fluorescence
changes and epifluorescence microscopy to quantify virus-like particle production. We have also
developed a protocol for growing lawns of Pseudo-nitzschia on solid media to enable individual
plaques to be picked for characterization. Our ultimate goal is to develop a genomically
characterized virus-host system to better understand bloom dynamics in the field.