Information Technology Reference
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a symbiotic relationship. It is now understood that many bacteria use molecular
signaling to initiate group behavior that is significantly more complex than
single organism behavior. These systems employ small, diffusible molecules
to accomplish cell-to-cell communication that leads to group behavior such
as the formation of biofilms or group bioluminescence. The organization of
microbial communities in biofilms is generally considered a predominant life
form of many prokaryotic and lower eukaryotic populations. Rather than an
amorphous assemblage of individual populations, biofilms exhibit structured
formation, assembly, and morphology and represent a rudimentary model of
prokaryotic development [24], in some ways analogous to tissues.
Recent developments in biofilm research have been extensively reviewed
[22, 26, 27]. What has become clear over the past decade is that there is a
well-recognized structural dynamic leading to mature biofilms, and there is
significant extracellular communication and control among members of biofilm
communities. The group nature of biofilms provides protection for individual
cells that allows survival in a hostile environment. Members of the biofilm enjoy
some protection from phage, biocides [16, 20] or potent antibiotics [75]. Fur-
thermore, the members of the biofilm community cooperate to promote survival
of the colony. Each cell in the community provides specialized functionality in
a complex community that has primitive homeostasis, a primitive circulatory
system, and cooperative metabolic activity [21].
The preceding three examples illustrate the significant abilities of cells
to sense, communicate, navigate, cooperate, and even to fabricate synthetic
nanoscopic materials. With these capabilities cells have the ability to inter-
act with, influence, and, to some degree, control their environment in a way
much coveted by designers of artificial systems. Having briefly considered this
functionality in natural systems, we now turn to a consideration of cells as
components in microscale and nanoscale systems.
CELLS AS COMPONENTS IN ENGINEERED SYSTEMS
There is a significant body of experience in the creation of sensing, information
processing, and actuating devices and systems from the combination of compo-
nents constructed from a variety of materials. Examples would include silicon
transistors, aluminum interconnects, silicon dioxide insulators, and carbon re-
sistors combined to form an electronic circuit. Fundamental properties of these
components determine both how they can be arranged within an information
pathway to produce a desired response to a given stimulus and how they can
be physically arranged on a common substrate. As components in these sys-
tems, cells reside in this environment, and the same component issues must be
addressed. These issues fall into four main categories:
