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Chapter 30 : Where Art Thou, O Nucleoid?

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Where Art Thou, O Nucleoid?, Page 1 of 2

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Abstract:

In a post on May 12, 2008, Elio asked where ribosomes are located in bacterial cells. According to a 2006 paper by Ortiz et al. (1.usa.gov/1NzRno7), “” and “.” This prompts one to also ask, “” Do their observations indeed indicate that, in the small cells of ( Figure E ; volume ~0.02 µm), the ribosomes (number ~1000) and DNA (genome size 1.46 Mbp) co-mingle and that a phase separation between cytoplasm and nucleoid is absent? In larger, fast-growing cells ( Figure B ; volume 1–3 µm), the nucleoid is clearly visible in living cells as a low-density compartment, as was already documented by Mason and Powelson in 1956. However, distinct nucleoids are difficult to see in smaller, slow-growing cells. In the small , nucleoids have even been reported to be absent (R.B. Jensen, 2006) (1.usa.gov/1jQ96ht). The existence of a discrete DNA phase was calculated by Odijk (1998) (1.usa.gov/1RdvvzJ), taking into account the excluded volume interactions between DNA and the soluble proteins as present in small cells ( Figure A ; volume 0.46 µm; genome size 4.6 Mbp). To me it seems unlikely that the physical laws that predict the visible phase separation in the larger cells would not hold for the smaller cells, as well.

Citation: Woldringh C. 2016. Where Art Thou, O Nucleoid?, p 123-125. In Schaechter M, In the Company of Microbes: 10 Years of Small Things Considered. ASM Press, Washington, DC. doi: 10.1128/9781555819606.ch30
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Citation: Woldringh C. 2016. Where Art Thou, O Nucleoid?, p 123-125. In Schaechter M, In the Company of Microbes: 10 Years of Small Things Considered. ASM Press, Washington, DC. doi: 10.1128/9781555819606.ch30
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Cell and nucleoid volume of different bacteria drawn to the same scale. (A) Living cells of B/r, grown in alanine-medium (doubling time 150 min) and stained with DAPI. Merged phase-contrast and fluorescent images. Figures B through E are schematic drawings; light areas in B, C, and D represent hypothetical nucleoid volumes. (B) Schematic drawing of a fast-growing cell (doubling time 20 min) containing about 4 chromosome equivalents. (C) cell grown in alanine medium (doubling time 150 min) containing about 1 chromosome equivalent. (D) . Dimensions from Borgnia et al., 2008. (E) . Dimensions from Ortiz et al., 2006. In D and E, these non-cylindrical organisms are represented as cylinders for ease of comparison.

Credit: Conrad Woldringh.

Citation: Woldringh C. 2016. Where Art Thou, O Nucleoid?, p 123-125. In Schaechter M, In the Company of Microbes: 10 Years of Small Things Considered. ASM Press, Washington, DC. doi: 10.1128/9781555819606.ch30
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Conrad Woldringh is a member of the Swammerdam Institute for Life Sciences at the University of Amsterdam, The Netherlands.

Citation: Woldringh C. 2016. Where Art Thou, O Nucleoid?, p 123-125. In Schaechter M, In the Company of Microbes: 10 Years of Small Things Considered. ASM Press, Washington, DC. doi: 10.1128/9781555819606.ch30
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