AsianScientist (Sep. 23, 2014) – Researchers have uncovered the complex symbiotic relationship between fungi, termites and their gut bacteria. The paper documenting their findings has been published in the Proceedings of the National Academy of Sciences.
Fungus-farming termites are dominant plant decomposers in subtropical Sub-Saharan Africa and Southeast Asia, where they in some areas decompose up to 90 percent of all dead plant material. They achieve near-complete plant decomposition through intricate multi-stage cooperation between the Termitomyces fungi and gut bacteria, with the termites managing these symbionts by providing gut compartments and nest infrastructure.
Termites manage their fungus farm in a highly structured way. Older termite workers collect plant material and bring it to the nest. Younger workers eat the plant material together with Termitomyces fungal spores, and this plant-spore mix is defecated as a new layer of fungus garden. Within the garden, Termitomyces rapidly grows on the plant substrate until it is utilized, after which older termites consume the fungus garden. By then, nearly all organic matter has been broken down.
In order to understand the symbiotic relationship between the fungi and termites, an international team of researchers from the University of Copenhagen and Beijing Genomics Institute (BGI) sequenced and analyzed the plant decomposition genes of a fungus-farming termite and its fungal crop, as well as the termite gut bacterial communities.
A remarkable 86 percent of all the glycoside hydrolase enzyme families known from living organisms were present in the farming symbiosis. The fungus coded for enzymes needed to handle complex carbohydrates, while gut microbes contributed enzymes for the final digestion of oligosaccharides. The first gut passage, thus, mainly serves to inoculate the plant substrate with fungal spores, while gut bacteria play a prominent digestive role during second gut passage.
The metagenomic analyses of the queen termite gut showed that it contained a highly simplified bacterial community lacking plant decomposition enzymes. This suggests that the royal pair is exempt from decomposition duties and receives a high-quality fungal diet from their workers.
Dr. Hu Haofu, the co-first author of this work from BGI, said, “The fungus-farming termites is a very unique species for their termite-fungus symbiosis. With the sequencing and analysis of the genome and the metagenome of the symbiotic partners, we can know more about the termites’ unique solution for lignocellulose digesting with the help from their gut bacteria.”
The article can be found at: Poulsen et al. (2014) Complementary Symbiont Contributions to Plant Decomposition in a Fungus-Farming Termite.
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Source: Beijing Genomics Institute; Photo: Filipe Fortes/Flickr/CC.
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