We now refer to free-floating (planktonic) viruses
within natural waters as virioplankton. This is
similar to calling planktonic bacteria-bacterio-
plankton or planktonic unicellular algae-phyto-
plankton. The discovery, over 15 years ago, of
the vast abundance of virioplankton lead to two central questions on the influence of viruses on co-existing populations of bacterio- and phytoplankton:
1) How does viral infection influence the net productivity (growth) of bacterio- and phytoplankton?
2) How do viruses alter the genetic composition of bacterio- and phytoplankton communities?
The Microbial Observatory for Virioplankton Ecology was established in May 2002, through a grant from the National Science Foundation, Microbial Observatories program. The overall goal of the project is examine interannual changes in the abundance, activity, and diversity of virioplankton over the yearly biological cycle of the Chesapeake Bay estuary. The Chesapeake was chosen as this marine ecosystem experiences dramatic seasonal changes in phytoplankton growth (primary productivity). Because it is a slightly stratified salt-wedge estuary, the Chesapeake presents dramatic changes in salinity, temperature and dissolved oxygen both along its length and from surface to bottom waters. Our initial suspicion that the dynamic nature of the Bay would be reflected within its smallest residents has been correct. To date, the MOVE project has made many important discoveries:
• Isolation of a virus, Chaetoceros Nuclear Inclusion Virus, CspNIV for short, which infects a diatom, an important group of phytoplankton in the Bay. Learn more.
• The Chesapeake contains a unique group of bacterial phytoplankton (cyanobacteria) that show peak abundance in late summer.Learn more.
• Similarly, the Chesapeake contains unique populations of viruses which infect cyanobacteria, also known as cyanophages. Learn more.
• Extraordinarily abundant populations of viruses can be found in the muddy sediments of the Chesapeake Learn more.
• Sediment viral populaitions also show annual patterns in abundance and diversity. Learn more.
• Virioplankton composition changes over the annual cycle demonstrating repetitive patterns in the presence of large genome viruses. Learn more.
• Chesapeake bacterioplankton also demonstrate repetitive annual patterns in composition. Learn more.
• Genetically Chesapeake virioplankton communities are extraordinarily diverse containing as many as 4,000 different strains of virus. Learn more.
• A new method for monitoring the growth of viral populations indicates that the impact of viral infection on bacterio- and phytoplankton mortality also varies seasonally and peaks in the fall and winter seasons. Learn more.
In Depth Summary:
The discovery and later acknowledgement that viruses are the most abundant class of microorganisms in aquatic environments is perhaps the best example of our ignorance as to the true nature of microbial communities. In the years since this epiphany, we have learned that in some environments viral infection accounts for a significant proportion of daily bacterial mortality; making viral lysis the most efficient means of transforming biomass into dissolved organic matter. Moreover, as viral infection is generally very host-specific, this process may be important in shaping the composition and diversity of co-existing plankton communities. To date the majority of virio-
plankton studies have concentrated on methods development; simpleenumeration and observational studies; and, to a more limited extent, examination of virioplankton diversity and com-
munity structure. In only a few cases, mainly focusing on enumeration, have virioplankton populations been examined in the context of an annual cycle. An important goal of this microbial observatory is to investigate the role of viruses in the annual biological cycle of a temperate estuary, the Chesapeake Bay. In this effort we will apply a suite of recently developed analyses to characterize the productivity, diversity and composition of Chesapeake Bay virioplankton over annual cycles. Coincident with these analyses will be efforts to bring novel phycoviruses and cyanophages into culture.
Initial investigations have focused on comparative studies of three methods for estimation of viral production (TdR incorporation, fluorescently-labeled virus (FLV) tracer, and dilution); isolation of cyanophage infecting strains of the unicellular cyanobacteria, Synechoccocus; and characterization of cyanophage and bacterioplankton populations using culture-independent approaches. Estimates of virioplankton production varied widely between the methods ranging from 0.1 to 7 x 106 viruses ml-1 h-1 for the same water sample. From these initial trials it appears the dilution approach will suffice for routine estimation of virioplankton production, however, each method has significant shortcomings. Several phages infecting green strains of Synechoccocus from Chesapeake Bay were isolated and characterized according to microscopy, plaque morphology and molecular phylogeny of the g20 gene. Terminal restriction fragment length polymorphism (TRFLP) analysis of g20 amplicons from cyanophage in Baltimore Harbor indicated dramatic seasonal variation in populations of these viruses. Similarly, populations of bacterioplankton showed strong seasonality in community structure as assessed by 16S rRNA denaturing gradient gel electrophoresis (DGGE). Finally, we are developing a novel approach to phenotypic characterization of bacterioplankton using proteomic tools. From a combination of 2-D gel electrophoresis and MALDI TOF MS several proteins were identified from bacterioplankton concentrates collected from Chesapeake Bay water samples. It is our hope that this approach will eventually lead to new insights on the connection between the structure of microbial communities (viruses, bacteria and phytoplankton) and the biogeochemical function they perform.
Webpage last updated 5 May 2006
Web Information Contact: Eric Wommack, wommack_at_dbi.udel.edu
Web Design Contact: Bekki Helton, rrhelton_at_udel.edu
MOVE Team Members 2006: L-R, Front: Dr. Eric Wommack, Bekki Helton, Danielle Winget; Middle: Kui Wang, Dr. Yoanna Eissler, Kurt Williamson; Back: Jinjun Kan, Dr. Wayne Coats, Dr. Feng Chen.