Dead plant materials are hard to break down, and there are just a few animal groups able of doing it. The major constraint is the recalcitrant nature of these stable biopolymers such as cellulose and lignin, making the matrix indigestible to animals and difficult to colonize for microorganisms. An ideal combination seems to be insects grinding the material, increasing its surface-to-volume ratio, allowing microorganisms to perform fast assimilation of the organic compounds into available energy and simple nutrients. This is why most of decomposers reveal intricate long-term relationships with microbial communities. This symbiosis is truly beneficial for both partners, as microorganisms find continuous income of food and stable environment inside a termite gut, and the host benefits from ingesting a share of the energy and nutrients produced during the lignocellulose matrix breakdown.
Symbionts in termite guts originate from three following domains: Archaea, Eubacteria and Eukaryota; members of at least two are always present. The flagellates [NS1] occur in all “lower” termites, as well as in the woodroach Cryptocercus, while they are missing in Termitidae altogether. Gut morphology and composition of gut microbiota is by far more diverse in “higher” termites, and get especially complicated structure and function in true soil-feeding termites.
The known functions of termite endosymbionts are as follows: (1) Sugar polymers (cellulose, hemicelloloses) breakdown to short chains, to be ingested by termites or other symbionts; (2) Absorption of oxygen and maintaining conditions suitable for lignocellulose fermentation; (3) Recycling the nitrogen waste, and providing nitrogen-rich substrates, even at the expense of fixing atmospheric nitrogen if needed; (4) Acetogenetic elimination of hydrogen, (5) Lignin breakdown and degradation of resulting aromatic compounds (demethylation, deacetylation, decarboxylation; (6) Ingestion of protein components of humus in soil-feeders.
The relationship between termites and their gut microbiota (endosymbionts) is a hot topic in current science, mostly thanks to advances in NGS (next generation sequencing) methods, and attempts to use termite associates in commercial fermentation chambers changing the dead organic matter into e.g. methane and N-enriched biomass. While relationships with termite endosymbionts belong to broadly studied topics, the occurrence of ectosymbiotic microorganisms is a mystery - apart from the notoriously known case of fungus-growing termites (Termitidae: Macrotermitinae), revealing associations with the symbiotic fungus Termitomyces (Basidiomycetes: Agaricales). At the same time, termites are known to alter their environment and among others to change composition of microbial communities in their environment, by selective supressing of certain strains and support of others. The same is true for termite nests, in which only a small part of the environmental microorganisms may live. We are studying these phenomena by field experiments and extensive sequencing of environmental samples of different nature with the hope to understand the importance of particular members of termite symbiotic associates.