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Pioneer 1(1): 31-32, 2006
LETTER
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BACTERIAL AGE
Bacterial Age
Shi V. Liu
Pioneer
Apex, NC 27502, USA
E-mail: [email protected]
(Received 2006-04-05; accepted 2006-04-06; published online 2006-04-08*)
HIGHLIGHT
What is the complete life span of bacteria? What is bacterial age? Does the mainstream definition of
bacterial age make a general and scientific sense? A paper written fifteen years ago may still hold some
very deep insight on this important biological issue.
ABSTRACT
Logical reasoning revealed that current mainstream view of bacterial “life” span in fact just refers to the
bacterial cell division cycle or, more precisely, a single reproduction cycle. The so-called bacterial “age” is
in fact the stage of bacterial reproduction. These fundamental microbiological errors, which form a
dichotomy in biology, are a result of the illusion of one mother bacterium divides into two daughter
bacteria. But an alternative view that the two bacteria formed from one bacterium are really the mother and
its daughter will bring our view of bacterial life to normal. Thus, bacterial life span and its age can be both
defined and measured with accurate chronological time.
KEY WORDS
Bacterial age, Bacterial life, Life cycle, Cell cycle, Reproduction cycle, Dichotomy, Dogma
The bacterial life span is currently considered to be the
same as the bacterial cell division cycle. Accordingly, the
cell division (reproduction) stage has been referred as the
“age” of the bacterium (1). The “age” distribution of an
exponential phase bacterial population has been
mathematically described by following equation,
f (x) = 2 1-x
where x is the “age” of cells measured as the cell
“generation” (population doubling) time from 0 to 1 (2).
This definition of “age” is different from that normally
used for macroorganisms such as animals and plants. For
these organisms the life cycle of an individual organism is
distinctively different from its reproduction cycle, and the
life cycle usually includes more than one reproduction
cycle. The reproduction event(s) contributes to the overall
aging process but is not the only aging mechanism.
How do we explain such a dichotomous view of age?
Apparently, our knowledge on the life spans of
macroorganisms is more reliable than those on bacteria.
This is because the life span of individual macroorganism
can be directly observed but similar observations on
bacteria have never been accomplished. Therefore there
are only two alternative explanations for this dichotomy:
either the bacteria do have a totally different aging
mechanism or our understanding on the bacterial age is
wrong. Most, if not all, bacteriologists assume the first
alternative is correct. However, if the bacteria are really
different from other higher life forms in this fundamental
living mechanism, what benefits, in terms of deciphering
our own aging mystery, do we get from studying
bacterial life? How could bacteria teach us fundamental
living principles at the single-cell level?
I believe that this age dichotomy is due to our
conceptual confusion. According to the recently proposed
bacterial life model (3), the mother bacterium does not die
Liu
BACTERIAL AGE
or transform into the daughter cell immediately after
division (reproduction). The relationship between the two
cells formed by the division is of mother-daughter type,
not the widely accepted twin-sister type. With these
understandings, the bacterial age can be established on the
true genealogical basis and a unified aging process can be
applied to various life forms.
The traditional “age” definition of bacteria refers only to
the different stages of bacterial reproduction. Since the
reproduction period is only a portion of the overall
bacterial development, this “age” definition is apparently
incomplete and inappropriate. In fact, this traditional
definition may only be applied to the exponentially
growing bacterial populations (4). The mathematical
formula used for the exponential phase cannot fit into the
“age” distribution patterns shown in the stationary and
death phase of the bacterial cultures. This suggests that
we really do not have a universal explanation for the
bacterial aging. As a matter of fact, some people claim
that bacteria as well as other unicellular microorganisms
do not senescent (5) since they appear to be immortal due
to their autonomous and continuous cell cycles (6).
The newly proposed bacterial life model (3) and the
bacterial age concept both point to a unification of biology
at the cellular level. This may lead the respective
researches into the similar path by clarifying the existing
confusions. In this sense, these theoretical discussions
are not trivial exercises. It has been often observed that
“in fields lacking conceptual coherence, there is also
usually a lack of effective experimental programs” (6). I
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hope that the new concepts of bacterial life and age will
stimulate some fruitful explorations in the future.
References and Notes
1. EC. Neidhardt, J.L. Ingraham, M. Schaechter,
Physiology of the bacterial cell: A molecular
approach (Sinauer Associates, Inc., Sunderland,
Massachusetts, 1990).
2. E.G. Powell, J . Gen. Microbiol. 15, 492 (1956); J.R.
Cook, T.W. James, in Synchrony in cell division and
growth , E. Zuethen, Ed. (Wiley, New York, 1964),
pp. 485-495.
3. S. Liu, (1991). (unpublished)
4. D. Lloyd, R.K. Poole, S.W. Edwards, The cell
division cycle: Temporal organization and control
of cellular growth and reproduction (Academic
Press, London, 1982).
5. M.R. Rose, Evolutionary biology of Aging (Oxford
University Press, New York, 1991); A. Comfort, The
biology of senescence (Elsevier-North Holland,
Amsterdam, 1979); J.E Danielli, A. Muggleton,
Gerontologia 3, 76 (1959).
6. O. Necas, in The microbial cell cycle , P. Nurse, E.
Streiblova, Eds. (CRC Press, Inc., Boca Raton,
Florida, 1984), pp. 1-6.
7. Acknowledgement. I thank Neal Adrian for helpful
comments.
* This paper was submitted to Science on 1991-07-24. Science rejected it on 1991-08-07. This publication
contains the exact content as submitted to Science, with later added highlight, abstract, and keywords.
Pioneer 1 (1): 31-32, 2006 (http://im1.biz/p)
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