The vast majority of species on Earth are single-celled. Most of these languish in obscurity – many have never even been named – but some of the relatively few species that have been studied exhibit remarkable abilities.
Many of these are physical: some micro-organisms are amazingly strong; others can hibernate for hundreds of thousands of years or thrive in environments so extreme that they would kill off most other life forms in a flash.
But many bacteria and protists also exhibit behaviour that looks remarkably intelligent. This behaviour isn't the result of conscious thought – the sort you find in humans and other complex animals – because single-celled organisms don't have nervous systems, let alone brains.
A better explanation is that they're "biological computers" with internal machinery that can process information (see our review of Wetware: A Computer in Every Living Cell). Here are some of the most striking examples of this "intelligent" behaviour from the New Scientist archive.
Bacteria talk to each other with chemicals. They do so for a host of reasons, some of them hard to understand unless you are another bacterium (or a dedicated bacteriologist), but one of the most straightforward is demonstrated by Bacillus subtilis.
If B. subtilis individuals are growing in a food-poor area, they release chemicals into their surroundings. These essentially tell their neighbours: "There's not much food here, so clear off or we'll both starve."
In response to these chemical messages, the other bacteria set themselves up further away, completely changing the shape of the colony.
See The secret language of bacteria.
Many single-celled organisms can work out how many other bacteria of their own species, are in their vicinity – an ability known as "quorum sensing".
Each individual bacterium releases a small amount of a chemical into the surrounding area – a chemical that it can detect through receptors on its outer wall. If there are lots of other bacteria around, all releasing the same chemical, levels can reach a critical point and trigger a change in behaviour.
Pathogenic (disease-causing) bacteria often use quorum sensing to decide when to launch an attack on their host. Once they have amassed in sufficient numbers to overwhelm the immune system, they collectively launch an assault on the body. Jamming their signals might provide us with a way to fight back.
See A billion bacteria brains are better than one.
Not only can bacteria be talkative and co-operative, but they also form communities. When they do, the result is a biofilm, most familiar as the thin layers of slime that coat the insides of water pipes, or kitchen surfaces in student residences. They're also found in biological refuges, like the inner linings of human digestive systems – anywhere, in fact, where there is plenty of water.
Many different species live side by side in these "bacterial cities", munching one another's wastes, cooperating to exploit food sources, and safeguarding one another from external threats – such as antibiotics.
See Slime city.
Many microbes can accelerate the rate at which their genes mutate. This allows them to obtain new abilities that may be helpful when conditions get tough. This is a risky strategy, since many of the new mutations will be harmful or even fatal and is, in effect, a last-ditch tactic when there's little left to lose.
Examples are legion: Escherichia coli mutates more rapidly when under stress (Science, DOI: 10.1126/science.1082240), and yeast has also been shown to perform the same trick (Critical Reviews in Biochemistry and Molecular Biology, DOI: 10.1080/10409230701507773).
During the early 1990s, researchers suggested that bacteria might have a way to "choose" mutations that would be particularly useful. This idea of directed mutation was extremely controversial, and by 2001 the evidence was stacked against it (Nature Reviews Genetics, DOI: 10.1038/35080556).
See Day of the mutators.
It's common knowledge that many animals can navigate across vast distances, migrating birds and honeybees being among the best-known examples. But microbes are also pretty good at it.
The single-celled algae collectively called Chlamydomonas swim towards light, but only if it is of a wavelength that they can use for photosynthesis.
Similarly, some bacteria move according to the presence of chemicals in their environment – a behaviour called chemotaxis. E. coli, for example, move like sharks on the trail of blood if a few molecules of food are dropped into their environment.
Another group of bacteria align themselves to the Earth's magnetic field, allowing them to head directly north or south (Science, DOI: 10.1126/science.170679). Known as magnetotactic bacteria, their special ability comes from specialised organelles loaded with magnetic crystals.
But perhaps the most striking feat of microbial navigation is performed by the slime mould Physarum polycephalum. This colony of amoeba-like organisms always finds the shortest route through a maze.
See Microbes on the move.
Learning and memory
When the amoeba Dictyostelium searches the surface of a Petri dish for food, it makes frequent turns. But it does not do so entirely randomly.
If it has just turned right, it is twice as likely to turn left as right on its next turn, and vice versa. In some way, it "remembers" which direction it last turned. Human sperm have the same ability.
E. coli goes one better. This bacterium spends part of its life cycle travelling through the human digestive system encountering different environments as it goes. In the course of its journey, it encounters the sugar lactose before it finds the related sugar, maltose. At its first taste of lactose, it switches on the biochemical machinery to digest it – but it also partially activates the machinery for maltose, so that it will be ready for a feast as soon as it is reached.
To show that this was not simply hard-wired, the researchers from Tel Aviv University grew E. coli for several months with lactose, but without maltose. They found that the bacteria gradually changed their behaviour, so that they no longer bothered to switch on the maltose-digesting system (Nature, DOI: 10.1038/nature08112).
Remarkable though these behaviours are, we have probably only scratched the surface of what single-celled organisms can do. With so many still entirely unknown to science, there must be plenty more surprises in store.
admin note :
berdasarkan artikel diatas dapat diambil kesimpulan bahwa
amuba lebih cerdas daripada yang kita pikirkan karena:
mereka adalah "komputer biologis" dengan mesin internal yang dapat memproses informasi (lihat ulasan kami Wetware: Sebuah Komputer di Setiap Cell Hidup). Berikut adalah beberapa contoh yang paling mencolok dari perilaku "cerdas" dari arsip New Scientist. 1.Komunikasi: Bakteri berbicara satu sama lain dengan bahan kimia.tetapi salah satu yang paling mudah dipahami adalah ditunjukkan oleh Bacillus subtilis.
2. dalam hal pengambilan keputusan : setiap bakteri akan mengeluarkan enzim untuk menandai lingkungan hidupnya, dan mereka akan berubah perilaku ketika mengetahui bahwa pada satu area yang sama terdapat ensim yang berlebihan dari bakteri yang sama.
pada bakteri patogen, mereka akan menggunakan quorum sensing, ketika mereka sudah merasa cukup, mereka akan melakukan serangan secara bersamaan. mereka sangat kooperatif.
3. beberapa bakteri bergerak sesuai dengan keberadaan bahan kimia di lingkungan mereka - sebuah perilaku yang disebut chemotaxis. Kelompok lain bakteri menyesuaikan diri dengan medan magnet bumi, yang memungkinkan mereka untuk memutar kepala langsung ke arah utara atau selatan
wow.... dan banyak lagi, yang harus kita pelajari... mencengangkan....