Antibiotic resistance fight could get a little help from ants

 

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A giant ant carries a dead fellow in the name of cleanliness.
Dupont/Wikipedia, CC BY-SA

Charlie Durant, University of Leicester and Rob Hammond, University of Leicester

The world is facing an antibiotics crisis. Due to overuse, many once-powerful drugs are now useless against certain strains of serious bacterial infections. So scientists are on the hunt for new ways to attack harmful microbes.

One possibility is to investigate how other species have evolved ways to defend themselves. A new study highlights how most ants, even from small colonies, produce antimicrobial chemicals in their bodily secretions. It also suggests those ants that don’t make these substances are likely to have some other method of controlling bacteria that could be investigated. So perhaps the answer to antibiotic resistance is under our feet.

Like humans, the more than 12,000 species of ants are all highly social. This behaviour increases the chance that they come into to contact with germs. Comparable to our towns and cities, ant colonies take communal living to the next level, with up to tens of millions of individuals cohabiting in a single nest.

Colony survival depends on worker ants going out into the environment to collect food. Workers return to their densely inhabited nests loaded with food, but also harmful microbes. Returning workers then share their food and their germs through mouth-to-mouth feeding – essentially vomiting into each other’s mouths.

If this wasn’t enough, the warm, moist conditions in ants’ nests make them ideal nurseries for disease-causing microbes. Finally, the members of almost all ants in a colony are related, so if one ant is susceptible to a germ, it is likely that many others will be, too.

Despite this longstanding threat of disease, ants are incredibly successful creatures. They dominate some environments and have diversified into thousands of species over 150m years of evolution. This suggests ants have found ways to deal with the high threat of disease. So what can we learn from them?

How ants deal with disease

Scientists have found that ants use a number of tricks to limit disease. Like humans, ants are exceptional cleaners. Many species have efficient waste-removal systems, ensuring diseased waste (including dead ants) is removed from the nest or contained in special chambers. They also regularly clean themselves and each other, and group together to disinfect contaminated ants.

You scratch my back…
Pull/Wikipedia, CC BY-SA

But even with good hygiene habits, disease can still be an issue. Ants have evolved ways around this by using their own form of medicine. For example, some ants, when infected, eat toxins such as hydrogen peroxide to fight disease. Others collect conifer resin, which they incorporate into their nests as a preventative measure. Some species of ant are able to produce formic acid, which combines with the resin to form a potent antimicrobial agent.

We also know that ants also produce their own antimicrobials in bodily secretions. Now researchers have tried to work out what affects how these chemicals are made. In a new study published in the journal Royal Society Open Science, researchers from Arizona State University investigated the antimicrobial activity of 20 ant species in the US living in nests with between 80 and 220,000 inhabitants.

The researchers predicted that larger nest species would produce more effective antimicrobials, because of a greater risk of coming into contact with disease. Testing external secretions against Staphylococcus epidermidis, a common bacterium not known to cause disease, showed that 60% of the ant species produced secretions with antimicrobial activity. But, surprisingly, 40% didn’t produce an antimicrobial that could kill the bacterium.

What’s more, species in larger colonies were no more likely to have antimicrobial activity than small colonies. This is surprising as it is generally thought that disease is more likely to be spread in larger colonies. The authors suggest that the 40% of ants without antimicrobial activity have other methods of controlling the spread of bacteria. But we also don’t know if these 40% produce antimicrobial agents that work against other microbes.

Antibiotics for the future?

This adds to the idea that ants could well be a good source of new antibiotics. Not only do ants produce their own antimicrobial agents, but they can also encourage other beneficial microbes to grow. For example, researchers recently discovered a bacterium living among one ant species that produces compounds capable of killing harmful bacteria resistant to conventional antibiotics, including the common superbug MRSA.

The ConversationMillions of years of evolution in a high-risk environment have made ants a potential source of vital antimicrobials. These substances still need to be turned into effective drugs and then trialled in humans. But the more we learn about the strategies ants use to fight disease, the more likely we are to uncover new ways to deal with the threat of resistant bacteria and disease.

Charlie Durant, PhD Candidate, Department of Genetics and Genome Biology, University of Leicester and Rob Hammond, Lecturer, Department of Genetics and Genome Biology, University of Leicester

This article was originally published on The Conversation. Read the original article.

Our rover could discover life on Mars – here’s what it would take to prove it

 

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Mars seen by Viking.
NASA / USGS

Claire Cousins, University of St Andrews

Finding past or present microbial life on Mars would without doubt be one of the greatest scientific discoveries of all time. And in just two years’ time, there’s a big opportunity to do so, with two rovers launching there to look for signs of life – Mars2020 by NASA and ExoMars by the European Space Agency and Roscosmos.

I am helping to develop one of the instruments for the ExoMars rover, which will be Europe’s first attempt to land a mobile platform on the red planet. It will also be the first rover to drill into the martian crust to a depth of two metres.

But the rover will not be the first to look for evidence of life. The Viking landers sent by NASA in the 1970s carried experiments designed to so. They were ultimately unsuccessful, but provided a wealth of information about Mars’ geology and atmosphere that comes in handy now. In fact, exploration over the last half-century has shown us that early Mars was once a dynamic and potentially habitable planet.

ExoMars prototype rover.
Mike Peel/wikipedia, CC BY-SA

While it is not completely impossible that life could exist on Mars today, ExoMars is primarily focused on looking for extinct life. Because there’s a risk it could contaminate the planet with microbes from Earth, it is not allowed to go near the sites where we think it’s possible that microbes could exist today.

Chemofossils are the best bet

On Earth, life constantly unfurls around us, leaving its mark on our planet every day. There are, however, a number of factors to contend with when looking for life on Mars. The first is that the lifeforms we are looking for are single-celled microorganisms, invisible to the naked eye. This is because life on Mars is unlikely to have progressed any further down the evolutionary path. This is actually not so strange – Earth itself was a world of single-celled life for two billion years or more.

Another issue is that the life we’re looking for would have existed three or four billion years ago. A lot can happen in that time – rocks preserving this evidence can be eroded away and redeposited, or buried deep beyond reach. Luckily, Mars does not have plate tectonics – the constant shifting about and recycling of the crust that we have on Earth – which means it’s a geological time capsule.

Because we are looking for evidence of long-dead microorganisms, the hunt for bio-signatures lies in the detection and identification of organic “chemofossils” – compounds that are left behind by the decomposition of life. These are different to organic compounds delivered to planets on the backs of meteorites, or those, such as methane, that can be produced by both geological and biological processes. No single compound will prove life once existed.

Rather, it will be distinctive patterns present in any organic compounds discovered that betray their biological origin. Lipids and amino acids, for example, are fundamental components to living things, but are also found in certain meteorites. The difference lies in finding evidence that shows a process of selection. Lipids left behind by degraded cell membranes will likely have a limited size range, and comprise an even number of carbons. Similarly, amino acids naturally exist in both left-handed and right-handed forms (like gloves), but for some reason life only uses the left-handed ones.

It is also possible for microorganisms to produce visible fossils in the rock record. When conditions allow, microbial mats (multilayered communities of microorganisms) can become interspersed with fine sediment, producing characteristic morphological structures in rocks that form subsequently. However, the specific environmental conditions required for this mean such deposits are unlikely to be discovered by a rover exploring just one small region of a whole planet.

Microbial mat on Earth.
Alicejmichel/wikipedia, CC BY-SA

So, the best bet will be looking for organic compounds, a task which falls to the Mars Organic Molecule Analyser (MOMA) – the largest instrument in the ExoMars rover payload.

One intriguing finding from the Viking landers was the absence of detectable organic compounds at the martian surface. This was unexpected – many organic compounds are found throughout the solar system that do not form through biological activity. Subsequent missions revealed that a combination of harsh chemistry and intense radiation effectively remove much of the organic material from the surface of Mars, regardless of its origin.

But more recently NASA’s Curiosity rover has begun to find some simple organic compounds, hinting at what may lie beneath. By analysing samples brought up from below the surface, MOMA will have a better shot at finding those organic biosignatures that have survived the ravages of time.

Confusing contamination

Before any search for biosignatures even begins, however, ExoMars will first need to find the right rocks. The landing sites shortlisted for the mission have, in part, been chosen based on their geological characteristics, including their age (more than 3.6 billion years old).

Panorama of Mars taken by the Opportunity rover.
NASA/JPL-Caltech/Malin Space Science Systems

If MOMA identifies organic molecules within the samples brought up by the drill, one of the first things will be to establish whether they are the result of contamination by any rogue Earth-based organics. While ExoMars is looking for alien life, it is designed to look for life that is based on the same fundamental chemistry as life on Earth. On one hand, this means highly sensitive instruments like MOMA can be designed that target biosignatures that we have a good understanding of, and therefore increase the likelihood that ExoMars will be a success.

The downside is that these instruments are also sensitive to life and organic molecules on Earth. To ensure terrestrial organic or microbiological stowaways are minimised, the rover and its instruments are built and assembled inside ultra clean rooms. Once on Mars, the rover will run a number of “blank” samples, which will show what, if any, contamination may be present.

Ultimately, finding strong evidence of extinct life on Mars, whether it be chemofossils or something more visible, will be just the first step. As with most scientific discoveries, it will be a gradual process, with evidence building up layer by layer until no other explanation exists. If the NASA Mars2020 rover also finds similarly tantalising evidence, then these discoveries will represent a step change in our understanding of life in general. And, while incredibly unlikely, it is of course possible that ExoMars chances upon some living martian microorganisms.

The ConversationWhether ExoMars hits the jackpot remains to be seen, but at the very least it will mark a new beginning for the search for life on Mars.

Claire Cousins, Research Fellow in Planetary Science, University of St Andrews

This article was originally published on The Conversation. Read the original article.