You are ten per cent human and ninety per cent microbe, according to an itch-inducing statistic produced by the Human Microbiome Project back in 2008. It found that bacteria greatly outnumber human cells, and over ten thousand different species of bacteria live inside every single person on the planet.
The “human microbiome” is a term used to describe the alien population inside our bodies, and it includes bacteria, fungi, and archaea (and here’s a video produced by NPR that does a good job of exploring the “Invisible Universe of the Human Microbiome”.) Although scientists are aware of the importance of the human microbiome in health – for example, dangerous bacteria like c. difficile appear to be held in check by other bacteria – it is still not fully understood how bacterial communities behave in relation to disease. However, a recent study published in journal mBio suggests that bacteria in our mouths behave differently depending on whether we are healthy or ill. These previously unknown findings could lead to improved ways of preventing or even reversing the gum disease periodontitis, a condition thought to affect more than half the adult population in the UK.
Traditionally, microbiologists have focused on comparing the different types of bacteria in healthy and diseased individuals, as opposed to looking at changes in the bacteria’s behavior. Much research in obesity, for example, has focused on trying to isolate the specific types of gut bacteria suspected to be responsible for inducing or reducing obesity. The current study was unique as it explored the interactions between the bacteria and their metabolism – that is, what they ate – as opposed to solely concentrating on the specific types of bacteria present.
The researchers, from the University of Texas at Austin, collected plaque samples from human participants suffering from periodontitis. The samples were taken from both healthy and infected areas of their mouths, in order for the researchers to compare the differences in bacterial behavior. The behavior was analysed using “shotgun metagenomic sequencing” technology, a supercomputing technique allowing researchers to observe which genes the bacteria expressed. Over one hundred and sixty thousand genes were analysed producing 28 to 85 million reads of RNA snippets. RNA is very similar to DNA: DNA can be thought of as the “blueprint” of the cell since it contains all the genetic instructions required by an organism to develop and function, whereas RNA assists DNA to encode genetic information and transport genetic material around the cell.
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The only notable change was the bacteria’s eating habits, which changed depending on whether the sample was taken from a healthy or a diseased environment.
Microbiologist and lead author of the study, Marvin Whiteley, explained:
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It doesn’t really matter what bacteria you have, because the communities are acting very similarly. So a healthy community has this metabolism, no matter what the members are; and a diseased community has a very different metabolism, no matter what the members are”.
The findings also showed that in diseased mouths, there are fewer types of bacteria present, whereas healthy mouths contain a more diverse range. This finding could suggest that healthy mouths “progressed” to being diseased, possibly through specific types of bacteria “kicking out” other types and eventually dominating the population.
Overall, the findings from this study could help to predict certain illnesses, and thus possibly lead the way to new preventative measures for common conditions such as periodontitis. Whitely concluded by saying:
Medicine is going to change a lot in the next 10 to 50 years. We’re going to be thinking about these sorts of questions a lot more, questions like what is your microbiome actually doing?”