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Appl. Environ. Microbiol., 07 1997, 2754-2758, Vol 63, No. 7
D Weichart, D McDougald, D Jacobs and S Kjelleberg
Low-temperature-induced nonculturable cells of the human pathogenic
bacterium Vibrio vulnificus retained significant amounts of nucleic acids
for more than 5 months. Upon permeabilization of fixed cells, however, an
increasing number of cold-incubated cells released the nucleic acids. This
indicates substantial degradation of DNA and RNA in nonculturable cells
prior to fixation. Treatment of permeabilized cells with DNase and RNase
allowed differential staining of DNA and RNA with the nucleic acid dye
4',6-diamidino-2-phenylindole (DAPI). Epifluorescence microscopy revealed
that the could-induced nonculturable populations of V. vulnificus are
highly heterogeneous with regard to their nucleic acid content. The
fraction of nonculturable cells which maintained DNA and RNA structures
decreased gradually during cold incubation. After 5 months at 5 degrees C,
less than 0.05% of the cells could be observed to retain DNA and RNA. In
parallel with the loss of nucleic acids, an increase in the concentrations
of UV-absorbing material in the culture supernatants was observed in
nonculturable-cell suspensions. It is hypothesized that there are two
phases of the formation of nonculturable cells of V. vulnificus: the first
involves a loss of culturability with maintenance of cellular integrity and
intact RNA and DNA (and thus possibly viability), and the second is
typified by a gradual degradation of nucleic acids, the products of which
partly remain inside the cells and partly diffuse into the extracellular
space. A small number of nonculturable cells, however, retain DNA and RNA,
and thus may be viable despite having reduced culturability.
Copyright © 1997, American Society for Microbiology
In situ analysis of nucleic acids in cold-induced nonculturable Vibrio vulnificus
School of Microbiology and Immunology, University of New South Wales, Sydney, Australia.
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