Spatial Pattern Formation of Motile Microorganisms: From Gravitactic Bioconvection to Protozoan Culture Dynamics - Porous Media: Applications in Biological Systems and Biotechnology - page 536

14.3.4 Key Results of Experimental Study ................................ 555
14.3.4.1 The Diffusion Regime ..................................... 555
14.3.4.2 The Stationary Convection Regime ....................... 556
14.3.4.3 Unsteady Convection Regime ............................. 556
14.3.4.4 Critical Threshold for the Transition...................... 557
14.4 Summary and Perspectives of Future Research ............................ 559
14.5 Appendix: Boussinesq Approximation for the Microorganism
Suspension .................................................................. 560
14.6 Nomenclature ............................................................... 561
14.7 References ................................................................... 562
14.1 Description and Literature Review of
Bioconvection
14.1.1 Overview
Studies of momentum, heat, and mass transports, originally developed as inde-
pendent branches of classical physics, have grown into a unified field of fun-
damental engineering sciences with applications ranging from biotechnology,
nanotechnology to environmental fluid mechanics. Within research fields of
mass transport in aqueous environment, we might distinguish diffusive sub-
stances such as salt and sugar from mobile microorganisms with self-driving
ability such as bacteria and algae playing a vital role in the nature. The
mobility is an essential physiological activity of microorganisms seeking out
new environment to colonize for continued growth and reproduction. Com-
plex sensing and signaling mechanisms that allow microorganisms to move in
response to external or internal cues have been described under the specific
terms of “ taxis ”or“ kinesis .” The directional responses are called taxis while
the nondirectional ones are kinesis . Once a signal is received and decoded,
individual movement may occur via mechanical processes such as propulsion
by flagella or cilia, or gliding mobility, which relies on the frictional movement
of membrane proteins against a surface to propel the microorganism forward
(Van Hamme et al. 2006). Generally speaking, the movement of swimming
organisms may be classified according to their responses to various stimu-
lating factors of the environment. Principal types of taxes are reported by
Eisenbach (2001).
The interactions between the motile microorganisms and the surround-
ing fluid cannot be predicted by the well-established theory of classical mass
transfer. Modeling the physiological activities of microorganisms constitutes
the necessary background to understand, predict, and direct their activities
as they are exposed to continually changing environmental conditions. Their
responses may be either migration to a more favorable habitat or adaptation