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Do microbes possess consciousness?
“What is the ultimate scope of science? Is it just the material attributes of our universe that is amenable to its methods, whereas our mental existence must forever lie outside its compass?” This question is raised by Roger Penrose in his book Shadows of the mind.
The answer of course is that there is no limit to the scientific domain. Consciousness is probably the most important issue of our existence, which needs to be more extensively researched by scientists all over the world.
How do we define consciousness, when in reality we do not understand its origin or its nature? As far as we know, consciousness is subjective and what is consciousness to us may not be the same for a plant or an amoeba. Yet there appears to be some sort of consciousness which is universally present.
One of the criteria used by biologists for defining life is its capability to respond to stimuli. How can one respond unless one is conscious? Is it necessary for an organism to have a brain like us to be conscious?
If we think beyond the brain paradigm, then the problem becomes easier to handle. We can then explore the natural world, from the higher animals to viruses, on an equal footing.
Let us consider some examples. Rabies virus enters the body via the saliva, which is introduced by the infected animals (mostly dogs) into the bite wound. The virus travels along the nerves of the bitten animal to the brain. It then selectively concentrates in the limbic system, where the emotional centres are located.
This causes a major change in the nature of the animal. A dog which was docile and obedient becomes aggressive and uncontrollable. It bites every animal in its vicinity, including its owner. This is the only way the virus can survive and propagate itself. How did the virus trace this complicated pathway to achieve its aim?
A protozoan parasite, Sarcocystis, is very widespread in nature and involves the voluntary muscles of the body. A species of Sarcocystis, S. singaporensis, has a ratpython cycle. The parasite develops in the python intestines, producing the infective stage (oocyst), which is passed in the python faeces. Rats eat the python faeces, because it contains a lot of organic matter, and in the process get infected.
The parasite then begins to develop in the rat muscles and makes them partly dysfunctional. Some rats develop gangrene of the limbs and also become blind. In short, the rat usually survives, unless it has ingested a large dose of oocysts, but it cannot run as fast as it would normally. It becomes an easier prey for the python and the parasite is able to complete its life cycle.
Filarial worms are nematodes (round worms), found in many parts of the tropics. They are dependent on insects for transmission from one host to another. Wuchereria bancrofti, a common filarial worm of humans, is transmitted by the mosquito. During their life cycle, microfilaria (embryos) circulate in the blood, waiting to be picked up by the mosquito. As the mosquitoes transmitting this parasite bite at night, the microfilaria appear in the blood during the night. If they were to appear during the day, they would not get picked up by the mosquito.
If they circulate both during the day and night, they would be wasting a great deal of energy. Similarly, there is another filarial worm called Loa loa, its microfilariae appearing during the day, because the vector is a day-biting fly (Chrysops).
Many biochemical explanations have been given to explain microfilarial periodicity. But it largely remains an enigma and an amazing demonstration of a parasite’s capability to regulate its behaviour towards the feeding habits of its vector.
There is a trematode (flat worm), called Leucochloridium macrostomum, which has snails as its intermediate host and song birds as its definitive host. The terrestrial snail is usually hidden in the vegetation and after getting infected by the parasite, there is a marked change in its behaviour and appearance.
The infective stage (cercaria) of the parasite migrate to the snails tentacles, which swell enormously, become bright green in colour and begin to pulsate at 50 beats per minute. The brightly coloured pulsating tentacles attract the song birds which eat up the snails. The song bird is the final destination of the parasite and by this extraordinary means it reaches its goal.
Polymorphus minutus is also a parasite of the birds and its intermediate host is a shrimp. The normal colour of the shrimp is brown or yellow, but after getting infected by the parasite it becomes blue. It has been shown experimentally that birds are more attracted to blue rather than brown shrimps. The change in the intermediate host’s colour, therefore, increases the possibility that the definitive host (bird) will get infected. It almost seems as if Polymorphous is aware of this fact and brings about the change in colour.
Fungi of the genera Hohenbuehelia and Pleurotus have devised traps to catch nematode larvae that may crawl over their fruiting bodies. They produce micro drops of an acid at the ends of their aerial hyphae and as soon as the nematodes come in contact with the acid they get paralysed. The hyphae then enter the nematode’s mouth and anus and eat up their tissues.
Like parasites, bacteria too show awareness of their surroundings. If offered sugar solution on the one hand and acid on the other, they would swim towards sugar and away from acid. Similarly, they can sense temperature, light and even magnetic fields. During conjugation (mating), they pass on to their susceptible brethren antibiotic resistance to enable them to survive exposure to antibiotics. Is this some sort of altruistic behaviour?
About ten years ago, John Cairns and his group at the Harvard School of Public Health reported that bacteria tend to show mutations likely to benefit them when put under stress by starvation. This is known as “directed mutation”, which goes against the widely held belief that mutations are always random.
Other workers have suggested that under stress, “hyper mutation” rather than “directed mutation” occurs. Even so, the bacteria are responding in a manner which gives them the best chance of survival.
Many antibiotics act when bacteria are dividing. Stanford University researchers recently showed that exposure to certain antibiotics triggers an SOS response in bacteria, resulting in the shutdown of DNA replication and transient dormancy, thus enabling their survival.
Scientists from the Weizmann Institute of Science in Israel reported that when the process of amoebic division gets stalled during separation, the amoeba gets help from their neighbours. An amoeba moves in to separate the dividing cells. Researchers noted that this is not an isolated case of help and this kind of “amoebic midwifery” is a routine happening.
To think that only we, the humans, have consciousness, has alienated us from nature and has led us to mercilessly exploit and destroy our ecosystem. If we accept that consciousness is universal, then our relationship with the entire animal and plant world will change and we will give up the idea that man has dominance over all the inhabitants of the Earth and that they were created to serve him.
Published with permission from World Scientific, the publishers of Prof Zaman’s book Life sciences for the non-scientist
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