Xylophagia

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The consumption of wood is called xylophagia (from ancient Greek ξύλον xylon , German 'wood' and φαγεῖν phageín , German ' to eat' ) .

biology

Wood is created during the secondary growth in thickness of higher plants through the incorporation of lignin into the original cell wall. Accordingly, wood mainly consists of a composite of lignin and the original cell wall components ( cellulose , hemicellulose and pectin ), which is known as lignocellulose . Only a limited number of organisms have developed the ability to dissolve lignocellulose back into its individual components that are suitable for their own needs. Another problem is the very limited nitrogen content of wood. Most xylophage organisms are therefore dependent on symbiotic microorganisms that can fix nitrogen .

Organisms that feed exclusively on wood are described as obligatory xylophagous, those that only occasionally feed on wood are described as facultative xylophagous. If only rotting dead wood is used as a source of food, one speaks of saproxylophagia .

Prokaryotes

Among the bacteria are in particular representatives of the Actinobacteria ( Rhodococcus ), the Firmicutes , the Bacteroidetes ( Bacteroides ), the Alphaproteobacteria ( Sphingomonas ), the Betaproteobacteria ( Burkholdia ) and the Gammaproteobacteria ( Teredinibacter ) capable of producing or breaking down cellulose enzymes that break down lignocellulose can. The abilities of the archaea to break down lignocellulose have only been little researched. Some archaea, such as Pyrococcus , are known to be able to break down lignocellulose at high temperatures.

Protists and unicellular eukaryotes

Protists of the genus Phytophthora produce a number of enzymes with which they can break down cellulose and hemicellulose in plant cell walls. Up to 19 different protists from the groups of the Parabasalia and the Oxymonads live in an enlargement of the rectum of lower termites , where they are responsible for the digestion of wood particles. It is known that unicellular green algae of the genus Chlamydomonas can process and utilize cellulose with the help of an endoglucanase .

Mushrooms (fungi)

Wood with brown rot (above) and white rot (below)

Xylophage mushrooms have developed two fundamentally different strategies for breaking down lignocellulose, which are traditionally referred to as white rot and brown rot . White rot causing fungi develop lignocellulose cellulose degrading enzymes ( cellulases ) as well as lignin degrading enzymes such as laccases , ligninase , manganese peroxidase or other peroxidases . These enzymes are usually too big to penetrate the woody cell walls and the breakdown only takes place on the surface of the cell walls. Fungi that cause brown rot, on the other hand, have lost a large part of their lignocellulose-degrading enzyme system and replaced it with a system in which oxygen radicals generated via Fenton reactions bring about the degradation.

Xylophage hose fungi , the cause of soft rot , also have cellulose-degrading enzymes. However, their ability to break down lignin is less pronounced than that of the mushrooms that cause white rot.

Mussels (Bivalvia)

Marine drilling clams (Teredinidae) and the related family of Xylophagaidae have produced xylophage forms. However, they are not able to completely produce the enzymes necessary for the breakdown of lignocellulose, but rely on the help of gammaproteobacteria ( Teredinibacter ). The symbionts live in specially formed cells (bacteriocytes) in the Deshayes glands of the mussel's gills. The symbiont enzymes which are suitable for digesting wood are apparently selectively transported into the digestive tract by the mussels.

Crustaceans (Crustacea)

Xylophagous amphipod Chelura terebrans

Among the marine crustaceans feed on each one species from the order of isopods ( Limnoria of) and from the order of amphipods ( Chelura ) of wood without that they need for the help of symbionts. The woodlice of the genus Limnoria use hemocyanin from their hemolymph to break down the basic structure of the lignocellulose and thus increase the effectiveness of their own cellulose-degrading enzymes.

Insects (Insecta)

Representatives of several orders of insects have independently adopted a xylophage diet in the course of their developmental history. The manifestations of xylophagia and the physiological adaptations necessary for this in insects are correspondingly diverse . Some cockroaches and termites, for example, rely on wood for food for the rest of their lives. In numerous other representatives of the holometabolic insects , however, xylophagia is limited to the larval stage .

Xylophage larval stages are found in butterflies ( Cossidae , Sesiidae ), hymenoptera ( Siricidae ) and numerous beetles ( Scarabaeoidea , Buprestidae , Bostrichidae , Ptinidae , Lymexylidae , Oedemeridae , Cerambycidae and Curculionoidea ).

Termites produce cellulase in their salivary glands and midgut. In the lower termites predigested wood particles migrate to the bulbous enlarged rectum where they from the symbiotic there, flagellated protist ( " flagellate ") phagocytosed be and processed. The flagellates are themselves associated with symbionts (bacteria and archaea) that live both on their cell surface and in their cytoplasm and are involved in the breakdown of the. Only these prokaryotes inhabit the rectum of the higher termites ; they lack the flagellates.

Sucker mouth and teeth of Panaque nigrolineatus

Termites are very closely related to cockroaches. The composition of the symbiotic bacterial community in the intestine of xylophagous cockroaches, however, differs significantly from that of termites and shows more similarity to omnivorous cockroaches. It was therefore concluded that xylophagia in cockroaches and termites developed independently of one another.

Vertebrates (vertebrata)

From Loricariids the genus Panaque is known to absorb large amounts of wood. Up to 70% of the contents of their digestive tract can consist of wood, which they scrape off branches and trunks lying in the water with their suction mouth and spoon-shaped teeth. However, it is still unclear whether they also primarily use the wood for nutrient production and thus actually practice xylophagy, which would offer them a survival advantage in times when nutrients are poor.

The fish are obviously not able to digest the wood themselves. However, your digestive tract contains fungi and bacteria that have the potential to break down cellulose and fix nitrogen.

Medicine and psychiatry

In medicine and psychiatry, xylophagia describes the compulsive consumption of wood by people. This particular eating disorder is considered a special form of pica syndrome .

See also

Individual evidence

  1. ↑ a b c d e f g SM Cragg, GT Beckham, NC Bruce, TDH Bugg, DL Distel, P. Dupree, A. Green Etxabe, BS Goodell, J. Jellison, JE McGeehan, SJ McQueen-Mason, K. Schnorr , PH Walton, JEM Watts & M. Zimmer: Lignocellulose degradation mechanisms across the Tree of Life. In: Current Opinion in Chemical Biology , Volume 29, 2015, pp. 108-119, ( full text ).
  2. ↑ a b c d R. McDonald, HJ Schreier & JEM Watts: Phylogenetic Analysis of Microbial Communities in Different Regions of the Gastrointestinal Tract in Panaque nigrolineatus, a Wood-Eating Fish. In: PLOS one , Volume 7, Number 10, 2012, e48018, doi : 10.1371 / journal.pone.0048018 .
  3. ^ AC Benke & JB Wallace: Influence of Wood on Invertebrate Communities in Streams and Rivers. In: SV Gregory, KL Boyer & AM Gurnell (eds.): The ecology and management of wood in world rivers , American Fisheries Society, Symposium 37, 2003, pp. 149–177, ( digitized ).
  4. ↑ a b c E. Chiappini & R. Nicoli Aldini: Morphological and physiological adaptations of wood-boring beetle larvae in timber. In: Journal of Entomological and Acarological Research , Volume 43, Number 2, 2011, pp. 47-59, ( digitized ).
  5. ↑ RM O'Connor, JM Fung, KH Sharp, JS Benner, C. McClung, S. Cushing, ER Lamkin, AI Fomenkov, B. Henrissat, YY Londer, MB Scholz, J. Posfai, St. Malfatti, SG Tringe, T. Woyke, RR Malmstrom, D. Coleman-Derr, MA Altamia, S. Dedrick, St. T. Kaluziak, MG Haygood & DL Distelb: Gill bacteria enable a novel digestive strategy in a wood-feeding mollusk. In: PNAS Plus , Volume 111, Number 47, 2014, pp. E5096 – E5104, doi : 10.1073 / pnas.1413110111 .
  6. ↑ DJ Wildish & SMC Robinson: Ultimate cause (s) of dwarfism in invertebrates: the case of driftwood talitrids. In: Evolutionary Ecology Research , Volume 17, 2016, pp. 685-698, ( digitized version ).
  7. ↑ K. Besser, GP Malyon, WS Eborall, G. Paro da Cunha, JG Filgueiras, A. Dowle, L. Cruz Garcia, SJ Page, R. Dupree, M. Kern, LD Gomez, Y. Li, L. Elias , F. Sabbadin, SE Mohamad, G. Pesante, C. Steele-King, E. Ribeiro de Azevedo, I. Polikarpov, P. Dupree, SM Cragg, NC Bruce & SJ McQueen-Mason: Hemocyanin facilitates lignocellulose digestion by wood- boring marine crustaceans. In: nature communications , Volume 9, 2018, Article No. 5125, doi : 10.1038 / s41467-018-07575-2 .
  8. ↑ N. Lampert, A. Mikaelyan & A. Brune: Diet is not the primary driver of bacterial community structure in the gut of litterfeeding cockroaches. In: BMC Microbiology , Volume 19, 2019, Article No. 238, doi : 10.1186 / s12866-019-1601-9 .
  9. ^ A b c CL Marden, R. McDonald, HJ Schreier & JEM Watts: Investigation into the fungal diversity within different regions of the gastrointestinal tract of Panaque nigrolineatus, a wood-eating fish. In: AIMS Microbiology , Volume 3, Number 4, 2017, pp. 749-761, doi : 10.3934 / microbiol.2017.4.749 .
  10. ^ T. Knecht: Pica - qualitative norm deviations of the appetite. In: M. Ledochowski (Ed.): Clinical Nutritional Medicine , Springer-Verlag, Vienna, 2010, ISBN 978-3-211-88899-5 , pp. 697-704, ( preview ).