The survival of bacteria containing r-plasmids

  • Mohammad I.A. El-Haffar

Student thesis: Doctoral ThesisDoctor of Philosophy


The quantitative minimal requirements of Escherichia coli K12 W3110,
with (R+) and without (R-) the R- plasmid RP1l were determined in anaerobic
batch culture using a chemically defined medium (CDM). Under these condition
the R+ strain had agreater requirement for K* than the R-, but a smaller
requirement for SO4² with other requirements being similar. In general,
the nutritional requirements under anaerobic conditions for both strains
were quantitatively greater than those under aerobic conditions.

The ability of the R- and R+ strains to survive in competition with
each other, at D~0.1 h7! was examined in the chemostat. When R- cells were
added to R+ cultures (in a ratio of 1:10), the R- strain took over under
glucose (G-lim) and phosphate (P-lim) limited conditions. In the reverse
experiments, the level of the R+ strain fluctuated about the original
inoculum level. The R+ strain did not disappear completely in these mixed
culture experiments. There was evidence that its persistence was possibly
due to preferential attachment to the vessel walls. ,In K -limited
conditions (K-lim), the R+ strain took over at low K concentrations, but
not when the Kt concentration was increased. Under the same condition
as used for competition experiments, the apparent Ky values of G-lim and
P-]im R- cultures were lower than those of R+ ones. With K -lim cells.
R+ cultures had lower K, values than R- at low K+ concentrations, but
similar valuesat higher concentrations. However, in all limitations the
apparent K, value increaseads the concentration of the growth limiting
nutrient in the inflowing medium increased. In K+-lim experiments R- and R+
small colony variants were detected on NA plates. These had similar
biochemical properties to those of the parent cultures. The experimental
conditions did not affect the stability of the plasmid.

The effect of various growth environments on the cell envelope was
investigated. Aerobic cultures had higher 2-keto-3 deoxyoctonic acid
contents, with wider variation between depletions and R- and R+ strains,
than had the anaerobic cultures. A protein with an apparent M. of 34,000
present under most growth conditions was absent from the R- strain grown
aerobically (K+-lim) and all iron-depleted cultures.

The R- plasmid decreased the resistance of E. coli to drying, but had
no effect on the sensitivity of cells to Tween 80 or to sodium deoxycholate.
Sensitivity to the latter was increased by anaerobiosis. Sensitivity to
NaCl depended upon the depleting nutrient.

The relevance of anaerobic competition and survival under adverse
conditions to persistence of R- plasmids in the wild is discussed.
Date of Award1985
Original languageEnglish


  • survival
  • bacteria
  • r-plasmids

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