Use Figure 2.1 to justify the assumption that a typical bacterial cell (that is, E. coli) has a surface area of 6 μm2 and a volume of 1μm3. Also, express this volume in Femtoliters. Make a corresponding estimate of the mass of such a bacterium.

(b) Roughly 2–3 kg of bacteria is harbored in your large intestine. Make an estimate of the total number of bacteria inhabiting your intestine. Estimate the total number of human cells in your body and compare the two figures.

(c) The claim is made by Whitman et al. (1998) that in the top 200 m of the world’s oceans, there are roughly 1028 prokaryotes. Work out the total volume taken up by these cells in m3 and km3. Compute their mean spacing. How many such cells are there per milliliter of ocean water?

2.

Minimal growth medium for bacteria such as E. coli includes various salts with characteristic concentrations in the mM range and a carbon source. The carbon source is typically glucose and it is used at 0.5% (a concentration of 0.5 g/100 mL). For nitrogen, minimal medium contains ammonium chloride (NH4Cl) with a concentration of 0.1 g/100 mL.

(a) Make an estimate of the number of carbon atoms it takes to make up the macromolecular contents of a bacterium such as E. coli. Similarly, make an estimate of the number of nitrogens it takes to make up the macromolecular contents of a bacterium? What about phosphate?

(b) How many cells can be grown in a 5 mL culture using minimal medium before the medium exhausts the carbon? How many cells can be grown in a 5 mL culture using minimal medium before the medium exhausts the nitrogen? Note that this estimate will be flawed because it neglects the energy cost of synthesizing the macromolecules of the cell.
 

Transcribed Image Text:

(A) (B) (C) (D) ZAW flagella 2 m pili DNA |1 m 5 m Figure 2.1: E.coli as a standard ruler for characterizing spatial scales. (A) Atomic-force microscopy (AFM) image of an E. coli cell, (B) electron micrograph of a sectioned E. coli bacterium, and (C) the E. coli ruler. (D) Bacteria on the head of a pin giving an impression of how our standard ruler compares with the dimensions of everyday objects. (A, courtesy of Ang Li; D, courtesy of Tony Brain.) (A) (B) (C) (D) ZAW flagella 2 m pili DNA |1 m 5 m Figure 2.1: E.coli as a standard ruler for characterizing spatial scales. (A) Atomic-force microscopy (AFM) image of an E. coli cell, (B) electron micrograph of a sectioned E. coli bacterium, and (C) the E. coli ruler. (D) Bacteria on the head of a pin giving an impression of how our standard ruler compares with the dimensions of everyday objects. (A, courtesy of Ang Li; D, courtesy of Tony Brain.)

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