Previous Article | Next Article ![]()
Applied and Environmental Microbiology, August 2000, p. 3160-3165, Vol. 66, No. 8
Department of Biology, University of North Carolina at
Charlotte, Charlotte, North Carolina 282231;
Department of Biochemistry, Stockholm University, S-10691
Stockholm, Sweden2; Section for Natural
Sciences, Södertörns Högskola, S-14104, Huddinge,
Sweden3; and General Surgery Research
Laboratory, Carolinas Medical Center, Charlotte, North Carolina
282034
Received 21 May 1999/Accepted 19 May 2000
The green fluorescent protein (GFP) gene, gfp, of the
jellyfish Aequorea victoria is being used as a reporter
system for gene expression and as a marker for tracking prokaryotes and
eukaryotes. Cells that have been genetically altered with the
gfp gene produce a protein that fluoresces when it is
excited by UV light. This unique phenotype allows
gfp-tagged cells to be specifically monitored by
nondestructive means. In this study we determined whether a gfp-tagged strain of Pseudomonas fluorescens
continued to fluoresce under conditions under which the cells were
starved, viable but nonculturable (VBNC), or dead. Epifluorescent
microscopy, flow cytometry, and spectrofluorometry were used to measure
fluorescence intensity in starved, VBNC, and dead or dying cells.
Results obtained by using flow cytometry indicated that microcosms
containing VBNC cells, which were obtained by incubation under stress
conditions (starvation at 37.5°C), fluoresced at an intensity that
was at least 80% of the intensity of nonstressed cultures. Similarly, microcosms containing starved cells incubated at 5 and 30°C had fluorescence intensities that were 90 to 110% of the intensity of
nonstressed cells. VBNC cells remained fluorescent during the entire
6-month incubation period. In addition, cells starved at 5 or 30°C
remained fluorescent for at least 11 months. Treatment of the cells
with UV light or incubation at 39 or 50°C resulted in a loss of GFP
from the cells. There was a strong correlation between cell death and
leakage of GFP from the cells, although the extent of leakage varied
depending on the treatment. Most dead cells were not GFP fluorescent,
but a small proportion of the dead cells retained some GFP at a lower
concentration than the concentration in live cells. Our results suggest
that gfp-tagged cells remain fluorescent following
starvation and entry into the VBNC state but that fluorescence is lost
when the cells die, presumably because membrane integrity is lost.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Effect of Starvation and the Viable-but-Nonculturable State on
Green Fluorescent Protein (GFP) Fluorescence in GFP-Tagged
Pseudomonas fluorescens A506
*
Corresponding author. Mailing address: Department of
Biology, University of North Carolina at Charlotte, 9201 University
City Blvd., Charlotte, NC 28223. Phone: (704) 547-4049. Fax: (704) 547-3457. E-mail: jdoliver{at}emailuncc.edu.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»