Buoyant density ofEscherichia coli is determined solely by the osmolarity of the culture medium

Abstract

In previous studies, we had shown that the buoyant density of Escherichia coli is determined by the osmolarity of the growth medium by varying the osmolarity of the medium with NaCl or sucrose. However, the buoyant density of the cells always exceeded that of the growth medium. Here we determined the effect of medium with a buoyant density greater than the expected buoyant density of cells by adding Nycodenz to Luria broth. Percoll gradients of cells were analyzed by laser light scattering. The buoyant density for 125- and 375-mOsM-grown cells was 0.002 g/ml and 0.003 g/ml more, respectively, for cells grown in the presence of Nycodenz than those grown without Nycodenz, while the buoyant density of 250-mOsM-grown cells was 0.005 g/ml less for cells grown in the presence of Nycodenz than those grown without Nycodenz. Cells grown in 500-mOsM medium with or without Nycodenz had the same buoyant density. The buoyant density of cultures grown in defined medium was the same as those grown in rich medium, with only the medium osmolarity correlating to buoyant density. We conclude from these experiments that neither buoyant density nor chemical make-up of the medium determines the buoyant density of cells grown in that medium. Only the medium osmolarity determines cell buoyant density, suggesting that E. coli has no mechanisms to sense buoyant density.

Directed molecular evolution of ADP-glucose pyrophosphorylase

“…A selection method based on buoyant density differences in bacteria that contain inclusions was developed (18)(19)(20). The buoyant density of E. coli can also be shifted by osmotic shock and depends on the osmolarity of the culture medium (21,22). To allow buoyant density differences achieved by differential accumulation of glycogen to be observable in a Percoll density gradient, the Percoll medium osmolarity was adjusted to be equal to that of the Kornberg's 2% glucose͞Kan50-enriched liquid medium in which the firstgeneration transformants were grown.…”

Experiments and a three‐phase computational fluid dynamics (CFD) simulation coupled with population balance equations of a stirred tank bioreactor for high cell density cultivation

“…Based on the literature, the standard state enthalpy and entropy of E. coli used in the current study were −97.8 kJ · mol −1 and −0.219 kJ · K −1 · mol −1 respectively. The value of the buoyant density and the diameter of E. coli extracted from the literature were 1100 ± 3 % kg · m −3 and 1 μm, respectively …”

“…The value of the buoyant density and the diameter of E. coli extracted from the literature were 1100 AE 3 % kg Á m À3 and 1 mm, respectively. [46]…”

Acoustofluidic medium exchange for preparation of electrocompetent bacteria using channel wall trapping

“…The resonance frequency of our device that we used for excitation was around 2 MHz, leading to a viscous boundary layer thickness of ∼0.4 μm in water. To approximate the acoustic contrast factor of E. coli , we took the buoyant density of E. coli analysed by Baldwin et al 82 and the acoustic impedance of cells derived by Olofsson et al 83 and ended up with a value of Φ ≈ 0.07. Thus, the critical radius for cells in our system is r c ≈ 0.95 μm.…”