Microbial Ecology

, Volume 13, Issue 1, pp 59–74

Viability of soil bacteria: Optimization of plate-counting technique and comparison between total counts and plate counts within different size groups

  • Rolf A. Olsen
  • Lars R. Bakken

DOI: 10.1007/BF02014963

Cite this article as:
Olsen, R.A. & Bakken, L.R. Microb Ecol (1987) 13: 59. doi:10.1007/BF02014963


Viable counts of heterotropic soil bacteria were 3–5 times higher on low-nutrient agar media compared with a series of conventional agar media. Substantial amounts of monosaccharides and amino acids were present in solid media made from distilled water and agar powder, and a salt-solution agar medium (without organic substrates added) gave practically the same colony counts as the low nutrient soil extract agar medium. MPN values were comparable to or lower than plate counts. A search for slow-growing cells in the negative MPN tubes by fluorescence microscopical examination after 3 months incubation was negative.

The viable counts were 2–4% of the total microscopical counts in different soils. Assuming that the colony-forming cells did not derive from the numerous “dwarf” cells present in soil, a calculated percent viability of the larger cells was about 10%. The ecological significance of the plate-counting technique is discussed.

Copyright information

© Springer-Verlag New York Inc. 1987

Authors and Affiliations

  • Rolf A. Olsen
    • 1
  • Lars R. Bakken
    • 1
  1. 1.Department of MicrobiologyAgricultural University of NorwayAas-NLHNorway