Symbiosis on the basis of alcohol

To grow a good harvest, you need to destroy weeds without damaging a valuable culture. The solution to the problem is offered by modern biotechnology: a murderous herbicide plus transgenic plants resistant to it. However, some types of beetles have mastered this technology tens of millions of years before a person. Insects live in a passpertured environment on which mushrooms resistant to ethanol are grown. They are eaten.

Our hero is the Ambrosian beetle XYLOSANDRUS GERMANUS (Fig. 1) . The Ambrosian beetles include about 3400 species of bark beetles (Scolytinae) and 1,400 species of planes (Platypodinae). They got their name thanks to symbiosis with mushrooms, mainly ascomycetes, generation of Ambrosiella and Raffaelea. The ancestors of these mushrooms were once free, but now they grow in galleries that beetles rush in soft wood under the bark itself. Larvae and adult insects live there and feed on mushrooms.

Males X. Germanus do not fly. The female founds the new nest and brings disputes of edible mushrooms with her, for this, on her body there are special relief structures - mycictia. Arranging a gallery, the female dwells in her disputes and, until they germinate, does not lay eggs, because the larvae will die without mushrooms.

Unfortunately, the “weed” mushrooms also fall into the bugs galleries, including Penicillium and Aspergillus . They interfere with the growth of the mushroom garden, and beetles have to protect crops from them. X. Germanus provides useful mushrooms with a fair start advantage, since the female brings with her and sowing a very large amount of dispute. In addition, beetles choose weakened or dead trees, the fabrics of which contain ethanol for the installation of nests. In some tissues of healthy trees, alcohol is also present, but in weakened it is more due to a lack of oxygen experienced by sick plants. At first glance, such behavior seems irrational, because ethanol is an antimicrobial agent that should harm the mushroom garden. Nevertheless, the Ambrosian beetles in search of a suitable tree are guided by the smell of ethyl alcohol. In healthy trees, they do not take root, the eggs do not lay down, and the mushrooms do not grow there.

The international group of researchers from the United States, Germany and Australia was convinced of this from experience. Scientists attracted beetles with a bait smelling ethanol to the trees of Kizil of the Blooming Cornus Forida and the Canadian Cercis Canadensis Bagrian [1] . Females willingly flew to the smell, but refused to settle in healthy trunks. Then scientists began to water plants with diluted alcohol of various concentrations so that life -giving moisture saturates the wood. The trees were thin, with a trunk diameter of 2.5–4.0 cm, planted in pots, so that alcohol went on an experiment with a reasonable amount. Plants that were watered with water were not interested in beetles. But in trees, poured with 1%-2.5%-or 5%ethanol solution, they arranged galleries, raised Ambrosiella Grosmanniae mushrooms and deduced offspring. The more concentrated the solution of alcohol was, the more it was in the wood of mushrooms and larvae. The result was no worse than in weakened trees inhabited by beetles in natural conditions.

By watering plants, you can pass the wood, but you can’t get the standard ethanol content in it in this way. And scientists made an artificial substrate from a mixture of kizilov sawdust, agar and malt extract and achieved a certain concentration of alcohol in it: 0; 0.1; 0.5; 1.0; 2.5 and 5%. The substrate was laid in plastic tubes and settled there female X. germanus. As the concentration of alcohol of biomass mushrooms and the number of larvae increased (Fig. 2). The optimal concentration of 2.5%turned out to be optimal. With a higher ethanol content, mushrooms and larvae grew worse, and refused to live in a 5%solution.

Researchers were convinced that A. Grosmanniae symbiotic mushrooms really tolerate alcohol, sowing them to a nutrient medium with different ethanol content. Mushrooms felt great in the presence of 1-2% alcohol, but a higher concentration harms them (Fig. 3). A similar picture was observed for the mushrooms of A. Roeperi and R. Canadensis , living in symbiosis with other types of rag -bustly beetles. At the same time, alcohol does not allow weed mushrooms to grow - aspergillus and penicillium : already with a concentration of 1% of their biomass, it decreases sharply.

Symbionni mushrooms feel well in the presence of ethanol, because the system of detoxification is working in their cells-an enzyme of alcohol dehydrogenase. In penicil-lane fungi, its activity is very small, in Aspergil there is practically no enzyme, and weeds will die. In addition, Ambrosiella use ethanol as a substrate. It is not surprising that the beetles fly on the smell of alcohol, which fertilizes their mushroom kindergarten and at the same time destroys weeds. Such, so to say, "Roundup".

Ambrose mushrooms are not the only microorganisms that can eat alcohol. This is done by some bacteria (Acinetobacter spp., Pseudomonas aeruginosa), many yeast and growing on trees Autumn Armillaria MELLEA. However, the Symbionts of the Ethanol beetle not only neutralize and use, they synthesize it, like many other alcohols. Only a few types of yeast are capable of this. It is not surprising that the yeast resistant to ethanol feels great in immortal mushroom gardens.

In turn, ragweed beetles are not the only insects that make mushrooms. For example, termites and ants do the same. They also face the problem of mushroom pests, but solve it with antibiotics. To do this, they have to attract symbiotic bacteria that these antibiotics synthesize.

So, Apterostigma dentigerum -leaf tags wear bacteria pseudonocardia sp. Removing the dentigerumicin antibiotic on the chest. There are so many these bacteria that on ant cover they are visible to the naked eye as a whitish plaque. The authors of the study suggested that the antibiotic suppresses the growth of parasitic fungi Escovopsis SP. [2]. Truth, according to other sources, is not specific dentigerumicin, it also harms mushroom plantings, so ants most likely use this antibiotic to clean the nest or protect insects from infection, but not for weeding [3].

Ambrosium beetles are spared the need to breed bacteria, because they have chosen the habitat correctly. However, no one says that there is no bacteria there. Many of the mushrooms adjacent to the Ambrosian beetles are resistant to cyclogoximide fungicide, which may indicate the presence of microbes that synthesize it. Many bacteria release antibiotics in stress conditions, therefore, ethanol is toxic, stressive substance - also stimulates microbial protection. So life in a passpertured environment has many advantages that beetles can use, because they themselves are stable to ethanol.

Natalia Reznik

1. Ranger CM et al. Symbiont Selection Via Alcohol Benefits Fungus Farming by Ambrosia Beetles // Proc Natl Acad Sci USA. 2018. 115. P. 4447-4452. DOI: 10.1073/pnas.1716852115

2. OH ​​D.-ch., Poulsen M., Currie Cr, Clardy J. Dentigerumycin: A Bacterial Mediator of Anth-Fungus Symbiosis // Nat Chem Biol. 2009. 5, 6. P. 391–393. DOI: 10.1038/nchembio.159

3. Sen R. et al. Generalized Antifungal Activity and 454-Screening of Pseudonocardia and Amycoratopsis Bacteria in Ness-Growing Ants // ProC Natl Acad Sci USA. 2009. 106. P. 17805-17810. DOI: 10.1073/pnas.0904827106