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Biotechnology and Society---Part
XV
Social life of bacteria
(In the Service of Mankind)
O wonderful! O wonderful! O wonderful!
I am food! I am food! I am food!
I eat food! I eat food! I eat food!
My name never dies, never dies, never dies!
I was born first in the first of the worlds, earlier than the gods, in the belly of what has no death!
Whoever gives me away has helped me the most!
I, who am food, eat the eater of food!
I have overcome this world!
He who knows this shines like the sun.
Such are the laws of the mystery!
- Taittiriya Upanishad (book 3, lesson 10)
Amity and enmity are normally
considered the affections of only animate beings high on the evolutionary scale.
Not exactly true. Inanimate objects like atoms do have their own likes and
dislikes. For example, the sodium atom would love to mate with a chlorine atom
with a voracious appetite to form sodium chloride, known as common salt. The
same sodium atom also knows how to co-exist with its own kind. Among animate
beings, even bacteria, lowest on the totem pole of living creatures, display
deep emotions and a sense of togetherness when needed. Among humans, we witness
cooperation as well as isolation as characteristics among individuals according
to the dictates of circumstances. Among lower species such as animals and
insects, cooperation is widely prevalent among one’s own kind of species. Did
sociality and cooperation originate with the primitive forms of life? Let us
take a look at the social life of bacteria and what we can learn from that.
Worms: Researchers have
recently discovered that tiny worms from a particular strain of C. elegans, do
not like to eat alone. When placed near food (a patch of bacteria in a gel
medium) they scurry around looking for company. Worms of another strain of C.
elegans clearly prefer solitude. Should we care about the social life of a tiny
worm? Perhaps, yes, mainly because we may have similar genes that dictate such
behaviour. The sociable worms were found to move around the food plate rapidly,
not slowing down until they found some eating companions. By contrast the
anti-social worms moved very slowly all the time grazing on food right from the
start. When their DNAs were analysed, it appeared that the difference amounted
to one codon (a triplet of nucleotides), resulting in one amino acid being
different in a single protein between the two classes. What a precise division
of classes!
Selfless bacteria?:
Bacteria are so ubiquitous that they are found on mountaintops, ocean bottoms,
guts of animals, hot springs and the Antarctic ice shelves. The ecosystem, on
land as well as water, depends on bacterial activity. The cycling of carbon,
nitrogen, and sulphur is completed by their tireless labour. When organisms die,
the carbon in their tissues is not available for most other living beings.
Bacteria break them down and release the nutrients to the environment. Plants
rely on nitrogen from the soil for growth and to make proteins. Only the soil
bacteria which coexist with the root system of plants make the gaseous nitrogen
in the atmosphere available to the plant in the form of soluble nitrogen.
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Sociality in bacteria:
Bacteria (born blind, deaf and mute) communicate with each other (just like
cells in our human body 'talk' to each other) through chemical signals as if
they are veritable social organisms. Many of them coexist in colonies which are
known as biofilms. When they do so they can protect themselves against
antibiotics and become resistant to other chemicals. They know the maxim,
'United, we stand'. In a colony all the bacteria may produce byproducts not for
themselves but simply to promote the welfare of the colony, i.e., to help their
brethren. Adapting to maximise exposure to air and nutrient-rich medium is
difficult for individual bacteria. In a colony it is a cooperative venture.
In the case of Pseudomonas
fluorescens, mutation allows them to make a polymer glue so that they can stick
together and form a film or mat. Each bacterium incurs a cost in producing the
glue which is neither useful for its own growth nor cell division but the group
as a whole benefits. Here we see a selection level where they sacrifice some of
their individual needs while contributing to the group. In this case, it is the
fittest group that survives, and not necessarily the fittest individuals.
However, this social tendency can rapidly degrade if they happen to be in an
asocial environment, like a homogeneous liquid culture medium.
How far do the bacteria go in
promoting sociality? Some researchers think that individual bacteria would even
die to keep the colony alive. It appears that if some bacterial cells are
damaged by antibiotics, they commit suicide so that the rest of the colony can
live. By killing themselves, the damaged cells no longer burden the colony but
their remnants provide needed nutrients for their kin and neighbours. However,
not all the bacteria in a colony commit suicide upon confronting a massive dose
of antibiotic. They shut down the cellular suicide mechanism since it does not
serve any purpose if all of them die.
Cells of a species called
Bacillus subtilis, when faced with starvation, compact themselves and become
dormant creatures called spores at which state they can stay alive for an
indefinite period. It is similar to the hibernation behaviour of bears. Here
again sociality is seen. When encountering starvation the cells align themselves
to form multi-cellular structures. The interior cells develop into spores, which
can remain dormant for hundreds of years. Here we see again a display of
cooperation. Sometimes they commit cannibalism during starvation. In other
words, they kill their neighbours in order to survive by utilising the remnants
of the dead bacteria. Although cannibalism appears, prima facie, a destructive
behaviour, it happens for the good of the species. As with cell suicide,
cannibalism is ultimately beneficial for the population as a whole, since it
delays or prevents sporulation for the entire population, which is only a last
resort under extreme conditions.
Networking: This
cooperation signifies a networking principle. What one bacterium cannot achieve
individually, it will achieve in conjunction with a multitude of its kind. This
concept is the forerunner for the modern network theory of information
processing using multiple computers and parallel processing. Pristine bacteria
mastered the art of universal information exchange.
As life forms became more
complex, they became less directly dependent on each other for survival. They
developed mimicry for transmitting knowledge. By observing their peer organisms
they learnt how to handle emergent situations. It is not strictly cooperation
but mutual learning. In the insect world, colonies of individual organisms
appear to exhibit powers not displayed by individual insects. Such coordinated
function has probably evolved from the colony-forming tendency of bacteria.
What
can we learn from the sociality of bacteria and other forms of life on
the evolutionary scale? Knowledge sharing and communication are
important for survival. The behavioural dynamics of the human
population indicates a connection to earlier patterns of communication
and knowledge-sharing evident in every species tracing back to the
earliest forms of life on this planet. However, as we noticed with
some colonies of bacteria where they resort to cannibalism, we notice
it among humans too but the end result is not the same. In the
bacterial world it was for the survival of the group. In the human
world it is for the survival of the individual. Did the 'selfless'
gene mutate along the evolutionary pathway?
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