Читать книгу Mutual Aid - Pablo Servigne - Страница 20

It’s time to turn to the species that not only are the ancestors of all those already mentioned (including us), but have also pursued their own evolution in association with other living organisms since the very beginning, 3.8 billion years ago. Bacteria are globally co-responsible for the evolution of all other living creatures and all ecosystems. Nothing less than that. In our culture, bacteria mainly make us think of illnesses. Yet only one species in 100,000 is pathogenic for us, the others being indifferent, harmless or beneficial.²⁹

Bacteria practise mutual aid at all levels. Within the same species, they very often form aggregates that allow them to survive more efficiently. In these extremely widespread ‘biofilms’, the bacteria in the centre assume a different form from those on the periphery,³⁰ and a complex chemical communication is established between all members of the colony, which can then be considered as analogous to a multicellular organism.³¹

Between different species, bacteria have developed amazing forms of mutual aid.³² When the conditions of the environment change, for example, they are capable of adapting quickly by exchanging fragments of genetic material with related species that may be better adapted to the new conditions. All of these incessant exchanges between billions of microorganisms resemble a kind of dynamic bacterial World Wide Web alongside which our own Internet is ridiculously simple. Bacteria thereby acquire such a degree of plasticity that we find them in such incredible environments as thermal springs, acid tars, Antarctic glaciers, the digestive tracts of animals, the sheet metal plates of the wreck of the Titanic, the tiny droplets in clouds and the deepest rocks.

The other species aren’t so stupid as to hesitate: the bacteria have done it all, and they might as well take advantage! So you want to use the huge reservoir of atmospheric nitrogen to make proteins? No worries, there are bacteria that control the process. They have even become the main sources of nitrogen injection into food chains. The legume family, which includes in particular clover, alfalfa, peas, beans and acacias, as well as 19,000 other species described so far, has developed root nodules that house the bacteria of the genus Rhizobium, which fix nitrogen.

What is less well known is that other plants, those that do not have nodules, attract other bacteria that fix nitrogen directly around their roots by transferring up to 10% of their sugars to them.³³ In another context, the association between the Anabaena nitrogen-fixing bacteria and the freshwater aquatic ferns of the Azolla genus allows the age-old rice fields of Asia to maintain their fertility without synthetic fertilizers. Given its great responsibility, this is a lovely floating plant which deserves greater renown.³⁴

Another symbiosis with nitrogen-fixing bacteria promotes the prosperity of the marine phytoplankton (a community essential to the production of oxygen on earth), especially dinoflagellates and diatoms with their delicate glass skeletons. The association is found almost exclusively in areas poor in nitrogen – showing the value of mutual aid when resources are scarce. An even more piquant aspect of the relation lies in the way that, when abundance returns, the hosts shed their symbionts!³⁵ When you live in abundance, help from others no longer seems necessary.

In addition to associating with plants, bacteria have become essential for animals, in particular for their digestive functions. They allow some insects, such as termites and bark beetles, to digest wood, aphids to enrich their diet, and beetles, flies, bugs, lice, cockroaches and cockroaches to feed on nutrients that are in principle difficult to digest.³⁶ One Chinese-American team even showed the ability acquired by a food moth caterpillar and flour worms to digest plastic (polyethylene and polystyrene, respectively), thanks to bacteria.³⁷ Apart from insects, digestive symbioses concern groups as diverse as molluscs (some shellfish have become specialists in the digestion of dead wood), leeches, sea cucumbers, crustaceans and mammals. A single cow rumen contains between 300 and 400 species of bacteria – a veritable microbial universe, to the point that some researchers call it the ‘nutritional superorganism’.³⁸

More importantly, bacteria are the source of life’s driving forces: photosynthesis and respiration. Photosynthesis, set up by cyanobacteria (known as blue algae), is no more and no less than the capacity of the living world to capture the light of the sun and store it in the form of large molecules (sugars and fats). Respiration, the reverse process, is the ability to use these molecules formed by photosynthesis as a source of energy. These two processes are the result of associations and fusions between bacteria.³⁹

It would be a shame not to add, even if we don’t have time to dwell on them here, the communities of animals living along the hot springs on the ocean floor, cultivating their symbiotic bacteria and able to live without oxygen on the basis of the minerals spat up by hydrothermal fluids; the many examples found in the oceans of animal bioluminescence provided by bacteria; the huge area of research into antibiotic bacteria, used by insects, corals, sponges, lichens and plants to protect against pathogens, and so on.⁴⁰ In short, bacteria, and especially mutual aid, are found everywhere; you just have to bend down to take a closer look.

During our research, we were surprised by the avalanche of very recent studies. It must be said that the dizzying acceleration of DNA sequencing finally allows all the bacteria present in any environment to be detected, where previously only those that were happy to grow on the culture media in labs were noted. The results are irrefutable: the propensity of bacteria to collaborate seems endless.⁴¹