Tal­mu­dic Ques­tion #112.2 Pre­ci­sion of Cell Di­vi­sion

by Con­rad Woldringh

In Tal­mu­dic Ques­tion #112, the ques­tion was asked: "Many, per­haps most bac­te­ria, di­vide into daugh­ter cells of al­most pre­cisely the same size. Why is that?"
 

Fig­ure 1. Mea­sure­ments from elec­tron mi­cro- graphs of agar fil­tered cells, taken from the the­sis of F.J. Trueba (Am­s­ter­dam, 1981). A E. coli B/rK grown in glucose+CASA min­i­mal medium. B E. coli B/rK grown in alanine+proline min­i­mal medium (im­age lost).

An an­swer may be found when mea­sur­ing the pre­ci­sion of cell di­vi­sion as a func­tion of cell shape. The pre­ci­sion of cell di­vi­sion is given by the co­ef­fi­cient of vari­a­tion (CV) of the ra­tio of the lengths of prospec­tive daugh­ter cells to the lengths of con­strict­ing cells (the so-called K(L) dis­tri­b­u­tion; Trueba, 1982). This CV varies with the shape of the cells as de­fined by the cell's as­pect ra­tio be­tween av­er­age cell length and cell di­am­e­ter (L/2R).

Mea­sure­ments of con­strict­ing cells pre­pared for elec­tron mi­croscopy by the method of agar fil­tra­tion (see Fig. 1, taken from the the­sis of F.J. Trueba, Am­s­ter­dam, 1981), show that fast grow­ing, thicker cells di­vide more pre­cisely (CV ≈ 5%) than the slow growing,thinner cells (CV ≈ 10%).

If nu­cleoid oc­clu­sion plays a role in sig­nal­ing cell di­vi­sion, the po­si­tion­ing of the whole, du­pli­cated nu­cleoid in the cell will in­flu­ence the site of di­vi­sion. As ev­i­dent from the im­ages of the cells in Fig. 2, that have about the same cel­lu­lar vol­ume and the same DNA-mass, the nu­cleoid has less space along the length axis of a thicker cell (Fig. 2A) than of the thin­ner cells (Fig. 2B), for geo­met­ri­cal rea­sons. Trueba (1982) sug­gested that if the po­si­tion of the nu­cleoid in the cell is more vari­able, so will be the site of cell di­vi­sion. As far as I know this has not been mea­sured di­rectly us­ing, for in­stance, DAPI-stained, liv­ing cells.

Fig­ure 2. Elec­tron mi­cro­graphs of thin-sec­tioned cells of two dif­fer­ent E. coli B/r strains. At dou­bling times ex­ceed­ing 60 min, the two strains have been shown to adopt widely dif­fer­ent cell shapes (Woldringh et al. (1977). A E. coli B/r ATCC12407 grow­ing with a dou­bling time of 90 min. B E. coli B/rK, dou­bling time 70 min. Note the nu­cleoid-free cell ends. A and B have the same mag­ni­fi­ca­tion.

The sug­ges­tion is only valid if the DNA mass is equally dis­persed within the vol­ume of the nu­cleoid; an­other Tal­mu­dic ques­tion?

 

Ref­er­ences

Trueba FJ (1982). On the pre­ci­sion and ac­cu­racy achieved by Es­cherichia coli cells at fis­sion about their mid­dle. Archives of Mi­cro­bi­ol­ogy, 131 (1), 55−59

Woldringh CL, de Jong MA, van den Berg W, Koppes L (1977). Mor­pho­log­i­cal analy­sis of the di­vi­sion cy­cle of two Es­cherichia coli sub­strains dur­ing slow growth. Jour­nal of Bac­te­ri­ol­ogy, 131 (1), 270−279. PMID 326763

 

Con­rad Woldringh is a re­tired mem­ber of the Swammer­dam In­sti­tute for Life Sci­ences at the Uni­ver­sity of Am­s­ter­dam.