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Appl. Environ. Microbiol., Apr 1996, 1311-1316, Vol 62, No. 4
AS Kaprelyants, GV Mukamolova, HM Davey and DB Kell
A high proportion of Micrococcus luteus cells in cultures which had been
starved for 3 to 6 months lost the ability to grow and form colonies on
agar plates but could be resuscitated from their dormancy by incubation in
an appropriate liquid medium (A. S. Kaprelyants and D. B. Kell, Appl.
Environ. Microbiol. 59:3187-3196, 1993). We used flow cytometry and cell
sorting to study populations of bacteria that had been starved for 5
months. These cells could be stained by the fluorescent lipophilic cation
rhodamine 123, but such staining was almost independent of metabolically
generated energy in that it was not affected by uncouplers. Two populations
could be distinguished, one with a lower degree of rhodamine fluorescence
(a degree of fluorescence referred to as region A and containing
approximately 80% of the cells) and one with a more elevated degree of
fluorescence (region B, approximately 20% of the cells). Subsequent
incubation of starved cells in fresh medium in the presence of the
antibiotic chloramphenicol (to which M. luteus is sensitive) resulted in
the transient appearance of cells actively accumulating rhodamine 123 (and
fluorescing in region B) and of larger cells exhibiting a yet-greater
degree of fluorescence (region C). These more fluorescent cells accounted
for as much as 50% of the total population, under conditions in which the
viable and total counts were constant. Thus, metabolic resuscitation of at
least one-half of the cells takes place under conditions in which cryptic
growth cannot play any role. Sorting experiments revealed that the great
majority of the viable cells in the starved population are concentrated in
regions B and C and that the extent of rhodamine staining under conditions
of starvation therefore reflects the physiological state of the cells.
Physical separation of these cells from cells in region A resulted in an
increase (of approximately 25-fold) in the viability of cells in regions B
and C and of the population as a whole. Resuscitation of dormant cells in a
most-probable-number assay in the presence of supernatant taken from
growing M. luteus revealed the resuscitation of cells from regions B and C
but not from region A. It is suggested that initially dormant
(resuscitable) cells are concentrated in regions B and C.
Copyright © 1996, American Society for Microbiology
Quantitative Analysis of the Physiological Heterogeneity within Starved Cultures of Micrococcus luteus by Flow Cytometry and Cell Sorting
Institute of Biological Sciences, University of Wales, Aberystwyth, Dyfed SY23 3DA, United Kingdom, and Bakh Institute of Biochemistry, Russian Academy of Sciences, Leninskii Prospekt 33, Moscow 117071, Russia
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