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The development of concentration gradients in a suspension of chemotactic bacteriaWhen a suspension of bacterial cells of the species Bacillus subtilis is placed in a chamber with its upper surface open to the atmosphere complex bioconvection patterns are observed. These arise because the cells: (1) are denser than water; and (2) usually swim upwards, so that the density of an initially uniform suspension becomes greater at the top than the bottom. When the vertical density gradient becomes large enough, an overturning instability occurs which ultimately evolves into the observed patterns. The reason that the cells swim upwards is that they are aerotactic, i.e., they swim up gradients of oxygen, and they consume oxygen. These properties are incorporated in conservation equations for the cell (N) and oxygen (C) concentrations, and these are solved in the pre-instability phase of development when N and C depend only on the vertical coordinate and time. Numerical results are obtained for both shallow- and deep-layer chambers, which are intrinsically different and require different mathematical and numerical treatments. It is found that, for both shallow and deep chambers, a thin boundary layer, densely packed with cells, forms near the surface. Beneath this layer the suspension becomes severely depleted of cells. Furthermore, in the deep chamber cases, a discontinuity in the cell concentration arises between this cell-depleted region and a cell-rich region further below, where no significant oxygen concentration gradients develop before the oxygen is fully consumed. The results obtained from the model are in good qualitative agreement with the experimental observations.
Document ID
20050000227
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Hillesdon, A. J.
(University of Leeds U.K)
Pedley, T. J.
Kessler, J. O.
Date Acquired
August 22, 2013
Publication Date
March 1, 1995
Publication Information
Publication: Bulletin of mathematical biology
Volume: 57
Issue: 2
ISSN: 0092-8240
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Cell Biology
Non-NASA Center
NASA Discipline Number 40-20
NASA Program Space Biology

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