All the Right Protists, in All the Right Places

by Joseph DeSisto

Given that it’s Termite Awareness Week, you may have already heard plenty about the destruction termites can wreak on homes and other man-made structures. But the termite’s ability to digest solid wood, while inconvenient, may work to our advantage. In several labs around the world, researchers are working to harness this ability to help produce biofuels from wood — efficient, renewable energy we can use.

Eastern subterranean termites (Reticulitermes flavipes) hard at work. Photo by Tom Murray.

Eastern subterranean termites (Reticulitermes flavipes) hard at work. Photo by Tom Murray.

Termites

Let’s start from the beginning. Termites are social insects that live in colonies, evolved from a lineage of cockroaches. What makes termites distinct from other cockroaches, aside from their behavior, is their ability to digest cellulose — termites are some of the few animals that can efficiently digest cellulose-rich materials such as grass and solid wood.

Enter Reticulitermes flavipes, the eastern subterranean termite. This species ranges widely in eastern North America from southern Canada to Texas. It also happens to be one of the most destructive termites in the region — millions of dollars are spent each year to control this species, which can eat its way through the wood in houses and other man-made structures.

Microbiome

But wait — termites can digest solid wood. It’s a well-known fact, but nonetheless worthy of a closer look. A much closer look in fact, because the termites can’t digest the wood by themselves: instead, the wood is chemically broken down by tiny protists in the termite gut (Ohkuma 2003). Just like humans, termites have a whole ecosystem of micro-organisms in their digestive systems but, frankly, theirs are a lot more kick-ass than ours.

The business end of an eastern subterranean termite (Reticulitermes flavipes). Photo by USGS.

The business end of an eastern subterranean termite (Reticulitermes flavipes). Photo by USGS.

In fact, each worker in a R. flavipes colony has roughly 59,000 protists belonging to at least 11 species (Lewis and Forschler 2004). Other species of termites, even those closely related to R. flavipes, have a few different protist species, and different concentrations of each protist. This is a reflection of the fact that each termite species has a slightly different role in the ecosystem — preferring different types of wood, for example, might require a different style of digestion.

Biofuels

Burning a log is a way to generate energy from wood, but isn’t that efficient. You couldn’t, for example, fuel a plane by tossing a bunch of logs in and lighting a match. But in labs around the world, chemical engineers are hoping to take wood and chemically convert it into usable fuel, just as corn is turned into ethanol. In combination with other renewable energy sources, wood-based biofuels could become a more efficient and environmentally friendly alternative to oil and natural gas.

A few members of a termite colony. The one with the big jaws is a soldier, here to guard the smaller workers, who do most of the wood-eating. Photo by Tom Murray.

A few members of a termite colony. The one with the big jaws is a soldier, here to guard the smaller workers, who do most of the wood-eating. Photo by Tom Murray.

Generating energy from wood is one thing, but doing so efficiently is hard. Chemistry is complex, and many important processes are difficult to perform in a lab setting. But in nature (and infested homes), termites and their protist symbionts have the skills we lack. They turn wood into useable energy, they do so efficiently, and they’ve been doing it for millions of years.

That’s why several research groups are studying the termite gut “microbiome” to see if they can harness this ability (Brune 2014). Each protist makes a particular chemical contribution to the digestion of wood, which takes place in many stages (Brune and Friedrich 2000). The ultimate goal is to replicate this in a lab setting, perhaps with large-scale artificial termite guts, loaded with all the right protists.

Trichonympha sp., a genus of protist -- species in this genus are found in the guts of termites, where they help break down wood. Photo by Tai et al.

Trichonympha sp., a genus of protist — species in this genus are found in the guts of termites, where they help break down wood. Photo by Tai et al.

There are many obstacles, however. Among them is the fact that, like many natural systems, the termite gut microbiome is way more complicated that we understand yet. Each protist species has a particular role in the long and laborious process of wood digestion. In addition, the termite gut isn’t uniform — it contains tiny habitats and climates, and each protist lives in a particular habitat within the gut depending on the oxygen level, available nutrients, and gut structure (Brune and Friedrich 2000). So, all the protists have to be there, and they all have to be in the right places.

Replicating the termite gut, in all its complexity, is a challenge, but through collaborations between microbiologists, engineers and, yes, taxonomists (it’s Taxonomist Appreciation Day, too), progress is being made. So, this Termite Awareness Week, remember to spread awareness of the fact that termites are not destructive — they are also useful, complex, and utterly amazing.

Cited:

Brune, A. 2014. Symbiotic digestion of lignocellulose in termite guts. Nature Reviews Microbiology 12: 168-180.

Brune, A. and M. Friedrich. 2000. Microecology of the termite gut: structure and function on a microscale. Current Opinion in Microbiology 3: 263-269.

Lewis, J.L. and B.T. Forschler. 2004. Protist communities from four castes and three species of Reticulitermes (Isoptera: Rhinotermitidae). Annals of the Entomological Society of America 97(6): 1242-1251.

Ohkuma, M. 2003. Termite symbiotic systems: efficient bio-recycling of lignocellulose. Applied Microbiology and Biotechnology 61(1): 1-9.

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