Teaching Resources

Our Animals

Headlines warning about “flesh-eating bacteria” or “deadly superbugs” inevitably attract more attention than a story about a glowing bacterium living peacefully inside a little-known squid. Yet, despite the spotlight on harmful microbes, most interactions between animals and microbes are actually mutually beneficial. Bioluminescent bacteria are a striking example: they colonize fish and squid, exchanging their light for food and shelter. At first glance, it may seem paradoxical that a microbe would spend so much energy producing light. What possible advantage could glowing offer to a tiny cell adrift in the ocean? In fact, some single-celled dinoflagellates can reach immense population densities in warm, nutrient-rich waters, creating visible “blooms.” These blooms, fueled by pollution and climate change, showcase how microbes use collective bioluminescence to confuse predators and survive.

Photo by Morro Bay, CA

Bioluminescent Microbes

Mum: I saw a wonderful show of blue waves on the shoreline last night, do these have anything to do with fireflies?

Most animals feed on plants or other animals, and humans are no exception. Unlike our ancestors, we rely on others to produce our food. This raises a question: why can’t we simply grow our own food or carry a backpack of plants to harvest when hungry?

Some animals and protists actually host microbes that act as a “living backpack,” converting CO₂ and small organic molecules into biomass using chemical energy, much like plants use sunlight. The host then consumes this microbial “harvest” while keeping conditions favorable for growth.

So why don’t more animals live this way? Because such systems only work where chemical energy is abundant, and most animals need far more food than they could ever carry. For example, feeding one human requires about 0.7 hectares of farmland—the size of a soccer field. Thinking about these microbial strategies helps us reflect on our own place as food consumers in a world of finite resources.

Animals with chemosynthetic symbionts

Why do we have to buy food at the shop? Why can’t we just grow all our own food at home?

Fruit flies encompass an exceptionally diverse group of insect species, varying in genetics, habitats, behaviors, and food sources. They have long served as a cornerstone of biological research, contributing to numerous discoveries across fields, including microbiology. One key finding is that the fruit fly microbiome plays an essential role in their health and development. At the same time, some fruit fly species are serious agricultural pests, causing extensive crop damage and generating billions of dollars in annual losses for control and monitoring efforts. Many flies, including invasive species, depend on microbes to break down plant material into forms they can digest, much like humans rely on gut microbes for food digestion. Beyond agriculture, fruit flies are also problematic in the food industry, particularly where decaying organic matter attracts them. Interestingly, certain microbes infect fruit flies and provide protection against predators and pathogens, and some of these microbial interactions are being harnessed to control agricultural pests and mosquito-borne diseases globally. Thus, fruit fly microbiology not only advances scientific understanding but also has direct implications for several Sustainable Development Goals (SDGs).

Image by Sanjay Acharya

Fruit flies and their microbes

Miss: Mum was so upset this morning because most of the apples she bought for my lunchbox had a circular area of rotting. What do you think caused this?

Often referred to as "the world’s greatest pandemic,” Wolbachia are among the most widespread microbial symbionts on Earth. They are present in roughly half of all arthropod species and in many nematodes. These bacteria primarily infect the reproductive organs of their hosts and are passed vertically from mother to offspring. Wolbachia employ remarkable strategies to manipulate host reproduction in order to spread through populations, and some strains can even block the transmission of human viral diseases such as Zika and dengue. For this reason, large-scale programs are releasing Wolbachia-infected mosquitoes to replace wild populations lacking the bacteria, thereby reducing viral transmission to humans. Moreover, certain pathogenic nematodes depend on Wolbachia for survival, prompting efforts to develop drugs that target the bacteria and, in turn, eliminate the nematodes responsible for debilitating human diseases. Excitingly, emerging research suggests new applications in agriculture, where Wolbachia may protect crops from insect-borne viruses. Altogether, Wolbachia-based strategies for arthropod and nematode control hold significant promise and contribute directly to multiple Sustainable Development Goals (SDGs).

Image by CDC, Professor Frank Collins

Insects: The Wolbachia Story

Sir: I saw a program on the TV where scientists are growing and releasing millions of mosquitoes outside. Why would they do that? A bacterium was mentioned

Whales are the largest animals on our blue planet, and some species—such as the blue whale—even surpass the size of the biggest dinosaurs. After decades of roaming the vast oceans, whales eventually die and sink to the seafloor or abyssal plain. Their bodies then provide a vital source of food for many organisms, including diverse microbes. Heterotrophic microbes break down the whale’s organic matter into compounds such as carbon dioxide, ammonia, and hydrogen sulfide, which in turn fuel the growth of chemoautotrophic microbes. This illustrates the natural balance of life in the ocean. However, pollution and commercial hunting continue to kill thousands of whales each year, threatening their survival and pushing some species toward extinction. Protecting the environment and enforcing effective whale conservation measures are therefore essential steps toward achieving the Sustainable Development Goals.

Whale Fall: an oasis of unique marine life on the seabed

Mum: what happens to whales when they die?

While certain termite species are damaging urban pests, responsible for significant wood damage, they make up less than 5% of the over 2,000 termite species. Most termites play a valuable role in ecosystems, particularly in recycling wood, grass, and leaf litter, though this can release methane, a potent greenhouse gas.

Termites feed on lignocellulose, a difficult-to-digest substance with low nitrogen content. To process this, termites rely on gut microbiomes to break down lignocellulose and supplement their diets with nitrogen. Understanding this symbiotic digestion process is key to grasping their environmental role and may offer solutions for eco-friendly biofuels from plant waste, while also helping manage greenhouse gas emissions.

Termites and their microbiome

Miss: last night I saw on TV enormous 4000 year-old termite mounds in Brazil that could be seen from satellites. But what do termites do?

Biologists aim to understand fundamental life principles: how organisms function, grow, develop, digest food, sense their environment, interact with other species, and evolve. Over the past century, their methods have evolved, shifting from observing organisms in nature to studying them in controlled laboratory settings.

Model organisms, such as bacteria, fungi, plants, and animals that are easy to grow in labs, are central to modern biology. One key model organism is the roundworm Caenorhabditis elegans, which has provided insights into basic biological processes. These findings benefit not only biologists but society at large, as they often reveal principles important for medicine and human health.

The nematode Caenorhabditis elegans as a model organism

Mum: Why do scientists study animals in the lab?

Blowflies

Have you ever noticed how they seem to find the most unexpected, and admittedly gross, food sources? It's as if they have a sixth sense for the weirdest and smelliest things.

Birds host a diverse array of microbes on their bodies (plumage, legs, beaks, eyes) and within their digestive systems. Most of these microbes are harmless and form mutually beneficial relationships, exchanging organic matter and molecules. While microbes assist birds in ecosystem tasks, they benefit from easier feeding and dispersal.

This lesson explores fascinating examples of bird-microbe interactions. We'll examine how microbes help woodpeckers build their nests and how some bird species use feathers in nests to combat pathogens. Additionally, we’ll discuss how microbes influence plumage color and the role of preen gland microbes in emitting odors for communication and mate selection. Lastly, we'll highlight the importance of gastrointestinal microbes in maintaining bird health.

Details of these remarkable interactions follow!

Illustration by Jose Arce Gómez

Birds and Microbiome

Maisy: How can woodpeckers possibly create nests in solid wood?

What are the reasons for recurrent mass mortalities of dolphins and seals? Are medical interventions to aquatic mammals sustainable? How can we help to avoid plague-like infection outbreaks in these species?

Photo by Noah Munivez from Pexels

Infections endangering wild aquatic aniamls

How can we help all these stranded dolphins?

Cattle, sheep, and goats are herbivorous mammals with a specialized gut structure that allows them to thrive on fibrous foods like grass. Their first stomach, the rumen, hosts microorganisms that break down plant fiber into volatile fatty acids (VFA), which are absorbed for energy and growth. These microorganisms also provide additional nutrients as they pass through the digestive tract.

Ruminants can turn pastures and rough ground into human-edible food, producing meat and dairy products that are staples in many cultures. However, this comes with environmental and health concerns. The ruminal fermentation process produces methane, a potent greenhouse gas, and ruminants’ nitrogen-rich urine and feces can pollute land and waterways. Additionally, overconsumption of ruminant meat and milk may pose health risks.

Microbes of rumen

Farmer Jones: do you know why cows can eat grass and we can’t?