Sammendrag
Appendicularians are planktonic marine tunicates with elaborate filter-feeding houses that can efficiently
trap particles as small as 0.2 lm. While marine viruses are seldom considered outside their role in disease
transmission, we conducted a controlled laboratory experiment to determine if the appendicularian Oikopleura
dioica can trap and ingest the Emiliania huxleyi virus (EhV; 160–180 nm diameter). Removal and retention
of EhV during 2.5 h and overnight incubations at 158C were measured using flow cytometry and
quantitative polymerase chain reaction specific for the mcp gene of EhV. The fate of retained EhV was tested
by quantifying EhV DNA in three biological compartments: house-trapping, ingestion/digestion, and defecation.
Clearance rates for EhV varied from approximately 2 mL ind21 d21 to 50 mL ind21 d21, with highest
rates for 4–5 d-old animals. EhV particles were cleared by O. dioica at rates similar to those reported for larger
food particles, with mean clearance rates in the 2.5 h incubations ranging from approximately 2 mL ind21
d21 to 50 mL ind21 d21. This demonstrates efficient virus removal by O. dioica and a previously overlooked
link between the microbial loop and the classical marine food web. EhV DNA was readily detectable above
background levels in O. dioica houses, gut contents, and faecal pellets, suggesting that appendicularian
houses and faecal pellets may contribute to the dispersal of viruses. Furthermore, clearance of EhV and presumably
other viruses by O. dioica may be a significant sink for viruses and thus an important factor in regulating
the population dynamics of viruses and their hosts.
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