title: Enumeration and biomass estimation of planktonic bacteria and viruses by transmission electron microscopy.
abstract: Bacteria and virus particles were harvested from water samples by ultracentrifugation directly onto Formvar-coated electron microscopy grids and counted in a transmission electron microscope. With this technique, we have counted and sized bacteria and viruses in marine water samples and during laboratory incubations. By X-ray microanalysis, we could determine the elemental composition and dry-matter content of individual bacteria. The dry weight/volume ratio for the bacteria was 600 fg of dry weight microns-3. The potassium content of the bacteria was normal compared with previous estimates from other bacterial assemblages; thus, this harvesting procedure did not disrupt the bacterial cells. Virus particles were, by an order of magnitude, more abundant than bacteria in marine coastal waters. During the first 5 to 7 days of incubation, the total number of viruses increased exponentially at a rate of 0.4 day-1 and thereafter declined. The high proliferation rate suggests that viral parasitism may affect mortality of bacteria in aquatic environments.
authors.affiliation: Department of Microbiology and Plant Physiology, University of Bergen, Norway.
authors.forename: K Y
authors.initials: KY
authors.lastname: Børsheim
authors.forename: G
authors.initials: G
authors.lastname: Bratbak
authors.forename: M
authors.initials: M
authors.lastname: Heldal
mesh_terms: D001419:Bacteria / Q000032:analysis / Q000254:growth & development / Q000648:ultrastructure*; D015169:Colony Count, Microbial; D004577:Electron Probe Microanalysis; D008828:Microbiological Techniques; D008854:Microscopy, Electron; D012623:Seawater; D014461:Ultracentrifugation; D014780:Viruses / Q000254:growth & development / Q000648:ultrastructure*; D014871:Water Microbiology