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UNRAVELLING THE MYSTERY OF THE TERMITE GUT

Steve Broadbent, Regional Director of Ensystex, takes a closer look at the microbial life that plays such a crucial role in the termite gut. 

 

We are all aware that the symbiotic microbes found in the termite gut and digestive tract are of great importance to termites, as they enable them to digest the lignocellulose found in wood. But what exactly are these microbes and how do termites acquire them? Seeking answers, an international team of scientists studied the gut symbionts of termites from Australia and North America.

The team of scientists from The University of Queensland and a number of US institutions studied the gut symbionts from seven higher and nine lower termite genera collected from Australia and North America. In performing this work, the entire gut structure of the termites was removed and pooled, before they were cultured to determine the microbial species present. This gave nearly half a million samples to be sequenced!

The two main types of microbes present were bacteria and archaea. Bacteria were shown to be the main microbial symbionts present, with 11 types found in more than half of the species collected. Archaea – single-cell organisms that have some distinct molecular features that separate them from bacteria – were also commonly found in Coptotermes spp., Schedorhinotermes spp., Porotermes spp., and Mastotermes darwiniensis.

The list of microbial organisms that were commonly encountered in nearly all species was extensive and included nine main groups of bacteria. It also include microbes belonging to the phylum Elusimicrobia. These microbes were first identified in the termite gut and were originally named ‘Termite Group 1’, but have since been found in other insects’ guts as well as in marine environments, sewage sludge, contaminated sites and soils, and toxic wastes.

The key difference between the gut pro les of the higher termites when compared to the lower termites was the presence of eukaryote protists in the lower termites only. Protists are organisms that have a defined cell nucleus, but are not an animal, plant, or fungus. These were replaced by Spirochaetes in the higher termites.

The most common Spirochaete genus found in termite guts was Treponema spp. This was found in the gut of every termite species analysed and appears to be essential for the survival of higher termites. Analysis of two Australian higher termite genera, Nasutitermes and Amitermes, showed Treponema were involved in all major functions that occur in the gut, which likely explains their widespread and long-term relationship with their termite hosts.

The data showed that changes in gut microbial populations have occurred mostly over evolutionary timescales – meaning termites have developed a specialised gut fauna and ora that meets their dietary needs. However, termites that feed on a range of foods (polyphagous) can adjust their gut microbial contents to allow them to adapt to seasonal variations or changes in available plant species. When feeding on wood, rather than grasses, these polyphagous termites tended to have higher numbers of Fibrobacteres and Spirochaetes (Spirochaetes are particularly associated with the digestion of wood) and a lesser number of Firmicutes.

Termites have evolved from a cockroach ancestor and then further evolved into eusocial insects that feed exclusively on lignocellulose. The move to this highly specialised diet was only possible due to the symbiotic relationship with these large numbers of microbes. It is these specialised microbes, bacteria and other single- celled organisms, that allow termites the unique ability to turn the cellulose in timber into energy, which is an extremely difficult process in itself. The variations in the gut microbe composition between different species also help in understanding termite evolution and how closely related the different species are.

So how do termites acquire these microbes? The clear inference from the study was that vertical inheritance from the parents was the main force that determined the composition of the microbes in the termites’ gut. Termites are very successful in passing on their gut microbes from one generation to the next.After inheriting gut organisms from their parents during nest foundation, nestmates can exchange gut symbionts between themselves, through trophallaxis (mouth to mouth feeding) or coprophagy (consumption of faeces) and/or proctodeal feeding (feeding from the anal region).

With much more to be learned about the termite gut microbiome, it is hoped that the availability of advanced genetic techniques and large-scale collaborations between multidisciplinary teams will reveal more answers about the functionality of the termite gut microbiomes and further understanding on the evolution of termites.

More information on termites

Steve Broadbent, Regional Director, Ensystex