Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Pioneer 1(1): 31-32, 2006 LETTER http://im1.biz/p © Truthfinding Cyberpress (http://im1.biz/tfcp) 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 32 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) ©Truthfinding Cyberpress (http://im1.biz/tfcp)