Researchers from the Institute for Integrative Systems Biology of Valencia (Spain) have won one of this year’s Ig Nobel prizes. Their work was published in the journal Scientific Reports. It was a study on the bacteria in chewed gums that end up on the ground. Yes, you read it right.

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The Ig Nobel prizes are a parody of the Nobel. They are awarded each year in early October to recognize the achievements of ten groups of scientists who “First they make people laugh and then they make them think.”

The awards are presented at an official ceremony organized at the Sanders Theater, Harvard University in the US The Ig Nobel thing is actually a game with the English word ignoble, which in Spanish means “ignoble.”

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All this may sound silly, but Andre Geim won the Ig Nobel in 2000 for “levitating a frog with magnets.” Ten years later, he won the Nobel Prize in Physics, the real one, for his studies on graphene.

Some curiosities about chewing gum

Before explaining what this work has consisted of and why it is so interesting, although at first glance it may not seem like it, I will tell you some curiosities about chewing gum.

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Chewing gum, chewing gum, has been used by humans Thousands of years ago.

Tooth marks have been found in Mesolithic and Neolithic wood tar resins suggesting that they were probably already used for cleaning teeth or as an adhesive.

However, the first commercial chewing gums as we know them now are from the late nineteenth century and today its consumption is massive.

Interestingly, in countries such as Iran and Saudi Arabia it is estimated that the 80% of the population consumes them on regular basis.

In Europe and the US more than 60% of adolescents and adults have chewed gum in the last six months and the average is between one and four a day.

In the US they have calculated that the chewing gum trade moves more than $ 30 billion a year (2019 data).

The composition of chewing gums is highly variable, but in general the majority component (between 20 and 30%) is non-digestible chewing gum, to which sugars, polyols (in formulations without sugar), colorants or flavorings are added. and antioxidants.

The rubber base can have a different composition: from natural polymers (such as latex or waxes) or synthetic (such as polyvinyl acetate), to synthetic elastomers (such as polyethylene, polyisoprene and others).

Unfortunately, chewing gum often ends up on the ground and must be spend millions of euros and many hours of work cleaning it.

In the United Kingdom it has been calculated that more than 70 million euros are spent a year on cleaning it. For this reason, there are research projects aimed at obtaining less adhesive, more water soluble and biodegradable rubbers.

What did you want to investigate in this job?

The authors wanted to characterize the bacterial composition of chewing gum, using classical culture techniques and metagenomics (complete DNA analysis).

To do this, they compared chewing gum samples collected from five different countries. The samples used were gum collected directly from the ground.

In total, they analyzed ten samples from Spain (Valencia University Science Park), France (Paris and Eurodisney), Greece (Spetses Island), Turkey (Istanbul) and Singapore. The samples were detached from the ground with a sterile spatula and stored in the laboratory at -80 ⁰C until analysis.

In addition, they wanted to study how the bacterial population of gum that has been in the soil for three months evolves and changes.

To do this, a healthy 36-year-old female volunteer chewed gum for 30 minutes (the corresponding informed consent had previously been obtained according to the guidelines of the 2013 Helsinki declaration).

One of the chewed gums was used as a control of the oral microbiota. Twelve others were placed on the ground in the open air, facing the sun, in mid-June.

Then each week, one of the gums was collected for a total of twelve weeks. DNA was extracted and sequenced (16S rRNA metagenomics).

The authors were also interested in studying the ability to degrade different gum ingredients by bacteria that they had previously isolated from gum.

Thus, they used two types of sugar-free gum. With them, they prepared a nutritional supplement that was added to the culture medium and then analyzed how some bacteria in the gum were capable of degrading it.

The results

The analysis of the bacterial composition of the chewing gums from the five different countries concluded that although there were differences between the samples, some bacterial genera they were found in all samples.

The chewing gums collected from various parts of the world contained a typical biofilm rich in bacteria such as Sphingomonas, Kocuria, Deinococcus, Blastococcus, among others.

As expected, many bacteria were environmental that resist radiation, need little water availability, endure variations in temperature and oxidative stress. The study did not allow characterizing a typical microbiome by country.

Taxonomic profiles of gum samples collected from soil from five different countries. (SATARI ET. AL.)

Regarding the study of the bacterial colonization process (see how the bacterial composition evolves once the gum is thrown on the ground), the control sample (the one that had been chewed for 30 minutes and had been directly analyzed without being thrown on the ground) turned out to be similar to the typical oral microbiota of the mouth with bacteria such as Rothia, Haemophilus, Corynebacterium, Veillonella, Actinomyces …

These mouth bacteria were detected throughout the experiment, but they decreased over time.

Throughout the weeks other environmental bacteria were increased, como Rubellimicrobium, Sphingomonas, Acinetobacter, Pseudomonas…

However, the most abundant bacterial genus in all samples it was Streptococcus. At first it was more than 25%, but then it decreased over time, reaching the minimum in the ninth week.

Dynamics of variation of microbial communities over twelve weeks.  The bars represent the modification of the microbial profile over time.  Satari et al.  (SATARI ET AL.)
Dynamics of variation of microbial communities over twelve weeks. The bars represent the modification of the microbial profile over time. Satari et al. (SATARI ET AL.)

To analyze how the chewing gum components could be degraded, they first grew samples, isolated some bacterial colonies and characterized them by sequencing their DNA.

Then they prepared a minimal culture medium to which they added an extract obtained from commercial chewing gums.

Thus, they analyzed whether any of the isolated bacteria was capable of degrading the chewing gum components. They found that several of them were capable of doing it.

But one strain in particular, of the genus Curtobacterium, was able to degrade almost all of the chewing gum ingredients that had been tested.

That is why the authors propose that this bacterium could perhaps be used as a bioremediation strategy to remove gum residues that contaminate our pavements.

In addition to how funny or curious this work may seem, the authors have shown that chewing gums can also harbor potential pathogens and that they could be a vehicle for the transmission of diseases.

This characterization of the chewing gum microbiota could be used to compare it with that of a person’s mouth, something that could be of legal interest or even forensic to know the perpetrator of a crime for the bacterial footprint that has remained in the gum that he threw at the scene of the murder.

Maybe it will end up being the script for one of the CSI chapters.

* By Ignacio López-Goñi, professor of microbiology at the University of Navarra. This article appeared on The Conversation. You can read the original version here.


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