Termite societies have highly structured divisions of labor, with a single royal pair, workers (old and new), and soldiers. But in order to decompose wood, some depend heavily on the fungus they farm and the bacteria in their guts. Now, researchers have sequenced the genomes of these termite farmers, their crops, and their microbes -- revealing a further subdivision of labor necessary for the complete breakdown of plant biomass for energy. According to the study, published in Proceedings of the National Academy of Sciences this week, termites evolved complex bioreactors 30 million years ago.
In some parts of Sub-Saharan Africa and Southeast Asia, fungus-farming termites decompose up to 90 percent of all dead plant material. They’re able to achieve this through the complex, multi-stage cooperation between fungi that they’ve cultivated and their gut bacteria. Termites manage these symbionts by providing nest infrastructure and gut compartments, respectively. To further investigate the various roles of these three players, an international team led by Michael Poulsen from University of Copenhagen and Guojie Zhang from China National Genebank analyzed the genes that make plant decomposition enzymes in the genomes of the fungus-farming termite Macrotermes natalensis, its Termitomyces fungal crop, and its bacterial gut communities.
Older termite workers collect plant material to bring back to the nest. Younger workers eat the plants together with fungal spores, and then defecate the plant-spore mix as a new layer of fungus garden. The fungus rapidly grows on the plant substrate until it’s all used up, after which older termites consume the fungus garden. By then, nearly all organic matter has been broken down.
“While we have so far focused on the fungus that feeds the termites, it is now clear that termite gut bacteria play a major role in giving the symbiosis its high efficiency,” Poulsen says in a new release. The first gut passage mainly serves to inoculate plant material with fungal spores, while bacteria play the prominent role during the second gut passage, leaving minimal waste.
A surprising 86 percent of all known families of plant-breaking enzymes (called glycoside hydrolase) were present in this farming symbiosis: that’s 111 enzyme families between all three. The fungus codes for enzymes needed to handle complex carbohydrates, while workers' gut microbes contribute enzymes for the final digestion of carbs called oligosaccharides. In this fungus farm -- or termite-run bioreactor -- the fungus does all the crude decomposition work, with the complementary bacteria delivering the final products.
Termite colonies are founded by a single queen and king. To grow her colony, the queen becomes an egg-laying machine, swelling up to gargantuan proportions. An examination of the queen’s gut reveals a highly simplified bacterial community without any plant decomposing enzymes -- which suggests that her royal highness has no decomposition duties and imbibes on a high-quality fungal diet she has delivered. Meanwhile, the short-lived workers and soldiers take care of all the colony duties. Here she is with a king and some workers:
Images: Saria Otani