Abstract

  "Viable but non-culturable" (VBNC) bacteria are a much discussed issue in microbial ecology. Quantitative aspects are not understood, due mostly to the lack of suitable techniques. A widely accepted approach is dependent on the integrity of cell membranes. Recently developed fluorescence dyes differ in permeability with respect to the integrity of membranes: one dye permeates the intact membranes, while another permeates those which are damaged. Although the dyes were developed originally for determining the viability of cultured bacteria, here they are used to enumerate live and dead bacterial cells (designated as having intact and damaged membranes, respectively) in natural environments. Preliminary results from coastal waters of Seto Inland Sea, Japan, were:
1) the sums of the intact and damaged cells were very similar in each case to the total number of acridine orange- stained cells; and 2) about 50-60% of the total bacteriaoplankton populations are intact with respect to membrane integrity.

Keywords: bacterioplankton, viability, eutrophication