scholarly journals Role of growth rate on the orientational alignment of Escherichia coli in a slit

2017 ◽  
Vol 4 (6) ◽  
pp. 170463 ◽  
Author(s):  
Julian Sheats ◽  
Bianca Sclavi ◽  
Marco Cosentino Lagomarsino ◽  
Pietro Cicuta ◽  
Kevin D. Dorfman
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Aspect Ratio ◽  
Density Fluctuations ◽  
Global Alignment ◽  
Similar Amount ◽  
Cell Area ◽  
Nematic Ordering ◽  
Side Walls

We present experimental data on the nematic alignment of Escherichia coli bacteria confined in a slit, with an emphasis on the effect of growth rate and corresponding changes in cell aspect ratio. Global alignment with the channel walls arises from the combination of local nematic ordering of nearby cells, induced by cell division and the elongated shape of the cells, and the preferential orientation of cells proximate to the side walls of the slit. Decreasing the growth rate leads to a decrease in alignment with the walls, which is attributed primarily to effects of changing cell aspect ratio rather than changes in the variance in cell area. Decreasing confinement also reduces the degree of alignment by a similar amount as a decrease in the growth rate, but the distribution of the degree of alignment differs. The onset of alignment with the channel walls is coincident with the slits reaching their steady-state occupancy and connected to the re-orientation of locally aligned regions with respect to the walls during density fluctuations.

On minimum aspect ratio for duct flow facilities and the role of side walls in generating secondary flows

2015 ◽  
Vol 16 (6) ◽  
pp. 588-606 ◽  
Author(s):  
Ricardo Vinuesa ◽  
Philipp Schlatter ◽  
Hassan M. Nagib
Keyword(s):  
Aspect Ratio ◽  
Secondary Flows ◽  
Duct Flow ◽  
Side Walls

scholarly journals Absolute requirement for polyamines for growth of Escherichia coli mutants (mnmE/G) defective in modification of the wobble anticodon of transfer-RNA

2019 ◽  
Vol 366 (10) ◽  
Author(s):  
Christopher Keller ◽  
Manas Chattopadhyay ◽  
Herbert Tabor
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Protein Biosynthesis ◽  
Transfer Rna ◽  
Coli Strain ◽  
E Coli ◽  
Wobble Position ◽  
Inhibition Of Growth ◽  
Absolute Requirement

Abstract The genes mnmE and mnmG are responsible for the modification of uridine 34, ‘the wobble position’ of many aminoacyl-tRNAs. Deletion of these genes affects the strength of the codon-anticodon interactions of the aminoacyl-tRNAs with the mRNAs and the ribosomes. However, deletion of these genes does not usually have a significant effect on the growth rate of the standard Escherichia coli strains. In contrast, we have found that if the host E. coli strain is deficient in the synthesis of polyamines, deletion of the mnmE or mnmG gene results in complete inhibition of growth unless the medium contains polyamines. The finding of an absolute requirement for polyamines in our current work will be significant in studies on polyamine function, in studies on the function of the mnmE/G genes, and in studies on the role of aminoacyl-tRNAs in protein biosynthesis.

scholarly journals Competition between Escherichia coli strains expressing either a periplasmic or a membrane-bound nitrate reductase: does Nap confer a selective advantage during nitrate-limited growth?

1999 ◽  
Vol 344 (1) ◽  
pp. 77-84 ◽  
Author(s):  
Laura C. POTTER ◽  
Paul MILLINGTON ◽  
Lesley GRIFFITHS ◽  
Gavin H. THOMAS ◽  
Jeffrey A. COLE
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Nitrate Reductase ◽  
Electron Acceptor ◽  
Physiological Role ◽  
Selective Advantage ◽  
Limited Growth ◽  
Terminal Electron Acceptor ◽  
Periplasmic Nitrate Reductase

The physiological role of the periplasmic nitrate reductase, Nap, one of the three nitrate reductases synthesized by Escherichia coli K-12, has been investigated. A series of double mutants that express only one nitrate reductase were grown anaerobically in batch cultures with glycerol as the non-fermentable carbon source and nitrate as the terminal electron acceptor. Only the strain expressing nitrate reductase A grew rapidly under these conditions. Introduction of a narL mutation severely decreased the growth rate of the nitrate reductase A strain, but enhanced the growth of the Nap+ strain. The ability to use nitrate as a terminal electron acceptor for anaerobic growth is therefore regulated primarily by the NarL protein at the level of transcription. Furthermore, the strain expressing nitrate reductase A had a substantial selective advantage in competition with the strain expressing only Nap during nitrate-sufficient continuous culture. However, the strain expressing Nap was preferentially selected during nitrate-limited continuous growth. The saturation constants for nitrate for the two strains (which numerically are equal to the nitrate concentrations at half of the maximum specific growth rate and therefore reflect the relative affinities for nitrate) were estimated using the integrated Monod equation to be 15 and 50 μM for Nap and nitrate reductase A respectively. This difference is sufficient to explain the selective advantage of the Nap+ strain during nitrate-limited growth. It is concluded that one physiological role of the periplasmic nitrate reductase of enteric bacteria is to enable bacteria to scavenge nitrate in nitrate-limited environments.

Linear growth rates for the Rayleigh-Bénard instability in cylindrical geometry

1981 ◽  
Vol 109 ◽  
pp. 339-348 ◽  
Author(s):  
J. N. Shaumeyer ◽  
R. P. Behringer ◽  
Ralph Baierlein
Keyword(s):  
Growth Rate ◽  
Aspect Ratio ◽  
Growth Rates ◽  
Linear Growth ◽  
Fluid Layer ◽  
Cylindrical Geometry ◽  
Experimental Measurements ◽  
Thermal Boundary Conditions ◽  
Side Walls ◽  
Rayleigh Benard

We report theoretical growth rates for the Rayleigh–Bénard instability when the fluid layer is contained by non-slip walls in a cylindrical geometry with diameter D and height L. Our results are for the growth rates of the first two axisymmetric modes as functions of the Prandtl number P and the aspect ratio γ≡D/2L. We have considered the two extreme cases of ideally insulating and ideally conducting side walls, and found that the growth rate is relatively insensitive to the choice of the thermal boundary conditions on the side walls. Our results are useful in understanding recent experimental measurements of the convective time-scale.

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