Geology Reference
In-Depth Information
Bacteria also produce other kinds of structures. Some secrete a dense, felty mat of long,
sticky fibres that grow from the cell membrane into the surroundings. These fibres,
known as the glycocalyx, help the cell to stick to surfaces such as soil particles, bare
rock and—in the case of
Streptococcus mutans
—to our teeth, where it causes tooth de-
cay as long as the sugar sucrose is present to provide the raw material of the glycocalyx.
Many different types of bacteria populate these sticky fibres in massive numbers, each
type making its own unique metabolic contribution to the whole, and each able to com-
municate in highly sophisticated ways which have only recently come to light. We tend
to think of bacteria as highly organised mindless matter, as nothing more than mere bags
of molecular trickery— sophisticated no doubt, but far from sentient, and with nothing
like the ability for sophisticated communication that is, we would like to think, the sole
preserve of our own species.
But recent findings bring this conclusion into question. Emergence cannot take place
without players that respond appropriately to the state of the whole, and bacteria are no
exception. Most bacteria live in communities, often with different cell types carrying out
specific metabolic functions, and in order for the whole to work well, the multifarious
and multitudinous members of the group have to communicate with each other about
the complexities of the surroundings which impinge on them, and about the state of the
whole community. Response requires communication. In us, in our fellow mammals, in
birds and in many insects, the major pathways of communication are sight, sound and
smell. Amongst bacteria there is no sight, no hearing, but there is something akin to
smell—the transmission of meaningful signals with which communication is possible,
thanks to a versatile language whose alphabet is a complex set of chemical messages.
One major channel of bacterial communication is known as
quorum sensing
. An amaz-
ing example lurks in the specialised light organs of certain squids.
We are snorkelling in a warm, shallow tropical sea on a bright moonlit night and oc-
casionally catch sight of a strange glowing shape swimming furtively near the bottom.
of being eaten by predators should the moonlight project its shadow onto the sea floor.
To avoid this danger, the squid engages in a cunning luminary deception: it emits light
that matches the intensity of moonlight on the bed of the sea, thereby camouflaging it-
self from shadow-seeking predators.
