Information Technology Reference
In-Depth Information
are capable of a tactic response to various chemical (chemotaxis) or physi-
cal (e.g., phototaxis) stimuli. Bacterial magnetotactic behavior was discovered
more than 25 years ago [12]. The examination of motile aquatic bacteria showed
that a magnetic field comparable to the geomagnetic field is enough to control
the direction of travel [38].
Magnetotactic bacteria fabricate nanoparticles of magnetite (Fe
3
O
4
[7, 39,
66, 68, 107]) or greigite (Fe
3
S
4
[6, 37, 50, 65]), enclose them in membranes
(magnetosomes [3]), and assemble these into linear arrays. This linear array
of magnetosome nanoparticles constitutes a permanent magnetic dipole fixed
within the bacterium [38] that is large enough to force orientation, and therefore
travel, along geomagnetic field lines.
Formation of Symbiotic Relationships
Sensing, information processing, and actuation by microorganisms might in-
volve communication with higher organisms. Such symbiotic relationships are
usually formed through a process in which a host becomes colonized by spe-
cific microorganisms from the surrounding environment. The mutual benefits
derived from these associations by host and symbionts are well documented.
However, only recently have the mechanisms by which the partners make con-
tact and establish a symbiosis been described. This process often requires com-
plex sensing, communication, information processing, and actuation from the
microorganisms.
For example, consider the inoculation of the Hawaiian squid,
Euprymna
scolopes
, with the luminescent bacteria
Vibrio fischeri
.
E. scolopes
has a light-
emitting organ that only functions when colonized by
V. fischeri
within its man-
tle cavity. During the inoculation process, the squid ventilates 1.3
l of seawater,
which on average contains only one
V. fischeri
cell, through the mantle cavity
every 0.5 sec [76]. If inoculation occurred only by random processes, during this
0.5-sec period the
V. fischeri
would have to find their way to one of only six 10-
µ
µ
m pores that lead into the light organ [76]. However, experiments performed
by Nyholm et al. [76] provided evidence that two-way communication between
V. fischeri
and
E. scolopes
mediates accumulation of
V. fischeri
and promotes the
colonization of the light organ. To enhance the symbiotic relationship,
V. fischeri
exhibit a loss of flagellation, reduction in cell size, decrease in growth rate, and
enhancement of luminescence soon after inoculation [88]. These events are
apparently catalyzed by
V. fischeri
sensing the light organ environment and
processing this information through changes in gene expression [111].
Biofilm Formation
The sensing, information processing, and actuation behavior of groups of mi-
croorganisms might be even more complex than that found in the formation of
