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When we hear the word extinction, one of the first things we think of are dinosaurs, perhaps followed by dodo birds, wooly mammoths and saber-toothed tigers. While there are an estimated 10-14 million species of animals living on this planet, there have been nearly 5 billion that have come and gone over Earth’s long evolutionary history. Earth has been around for a very long time, and through the tumultuous millennia of this planet, there have been many species to rise and fall.
However, one type of life on Earth—bacteria—is often overlooked, even when it comes to their rate of extinction! As talk of extinction and global climate disaster has increased in recent years, it has led more and more people to ask one simple questions—is it possible for bacteria to go extinct?
The History of Bacteria
A quick review of bacteria and its role on this planet may help to shed some light (and perspective) on this question.
For the past 3.5 billion years—and perhaps longer, according to some estimates—bacteria have been a part of life of Earth. Although they weren’t widespread until about 2 billion years ago, bacteria have now filled in every available niche on the planet, including some of the most extreme and inaccessible environments we know of, such as volcanic hot springs and subzero temperatures. From a common precursor, the Bacteria and Archaea taxonomic branches formed, while Eukaryotes developed later.
When it comes to discussing the diversity of bacteria, it’s quite impressive. While only 10,000 species have ever been grown in a lab, and only 100,000 have been thoroughly studied, a new estimate puts the likely number of microbial species on Earth at roughly 1 trillion. Yes, that’s trillion with a T. That number is nearly impossible to conceptualize, particularly in terms of species number. Remember, there are an estimated 1-2 million species of animals, and about 400,000 plant species, which both seem like significant amounts in their own right, but they pale in comparison to microbial life.
This brings up an obvious question—why is microbial life so much more diverse than other types of life on the planet? Yes, it has been around much longer, but that doesn’t explain the exponentially larger number. Fortunately, research has clearly hinted at the reason for this. The relatively simple structure of bacteria means that it has the ability to evolve quite quickly. There is quite a bit of genetic exchange in the bacterial world, even from distantly related organisms, so the genetic makeup of bacteria can change rather rapidly. There is also the effect of transposons, structures on these bacterial chromosomes that can rearrange genes, which can result in the rapid diversification of bacterial species. In fact, this is one of the major problems in modern medicine; bacterial resistance has been on the rise since the discovery of antibiotics in the 20th century, and since bacteria can adapt and evolve so quickly, they are often able to overcome the effects of a given antibiotic in a matter of years, if not quicker.
Bacteria and Extinction
For a very long time, most researchers believed that bacteria didn’t go extinct, based purely on their huge numbers, prolific spread across the globe, and ability to survive in such extreme conditions. The scale of a calamity that it would take to wipe a bacterial species off the face of the Earth would simply be too great. After all, humans had already proved that bacteria had survived numerous Ice Ages, when almost all other forms of life withered or died out entirely. Not only that, but proving that an extinct bacterial species existed would be difficult, considering their microscopic size and lack of ability to be fossilized.
Even so, recent advances in genetic sequencing technology have given researchers a clearer view of bacterial evolution, and it has been found that many bacterial species have gone extinct over their 3.5-billion year tenure on this planet. A decade or so ago, this level of computational and analytical power wasn’t available, so early estimates of bacterial relatedness were incomplete or incorrect. Nearly 450,000 different species of bacteria were sequenced, and that data was combined with information from more than 50 other bacterial studies to create the most comprehensive bacterial tree of life in history. Researchers from the University of British Columbia, who headed this study, relied heavily on the gaps in the evolutionary tree that were hinted at by speciation.
More simply put, there are genetic markers in any genetic code, and the absence or presence of specific markers can denote closeness of relativity. By compiling genetic codes from nearly half a million species of bacteria, some of which have been around for nearly a billion years, it is possible to see a complete picture. Imagine putting together a 5,000-piece puzzle, but only having 15% of the picture done. You may not be able to see all the details, but you might be able to guess what the complete picture will look like. With this type of research, the gaps in the genetic code become as informative as the data that isn’t missing.
Although these revelations are somewhat recent, and additional bacterial species are being sequenced all the time, it is believed that billions of bacterial species have come and gone, similar to other forms of life, i.e., animals and plants. The early belief that bacteria are partially immune to mass extinction events may be true, but that doesn’t mean they never go extinct. Due, in fact, to their rapid penchant for evolution and adaptation, it is believed that most microbial extinctions occur as a result of competition from a more advanced or well-adapted species in the area. Bacteria can be brutal in their desire to spread and conquer, so the complete elimination of a competing bacteria is far from impossible.
Can Bacteria Come Back From the Dead?
With the rise of climate change and melting icecaps, the idea of zombie bacteria from the past has become a new hot topic. Essentially, as permafrost melts in certain parts of the world, where it has been frozen for thousands upon thousands of years, it is feared that long-dead microbes might come “back to life”, potentially infecting human populations and leading to a massive epidemic for which we are not prepared. The question is—how realistic is that worry?
Bacteria can go through periods of dormancy, wherein they may lack any food resources nearby and will shut down their photosynthetic or metabolic processes. Without any resources to function, the cell “stops” and appears to be dead, but can be brought “back to life” when nitrates or other energy sources are made available—often returning to its normal patterns of cellular division within 48 hours.
Although it makes for a good headline, there has been absolutely no proof of zombie bacteria rising again out of the permafrost to sweep across the world. When bodies of those who had died from the Influenza epidemic of 1918 were dug up from the permafrost and studied, the cells of the bacteria were completely dead. The same thing was found in smallpox victims recovered as the temperatures begin to rise around the world. A bacterium that could affect humans is adapted to survive in the temperature of a living body, not in frozen soil for hundreds of years. While bacteria are incredibly hardy, surviving after millennia in the tundras of Siberia are still, apparently, too much for them to handle!
- The University Of British Columbia
- Encyclopædia Britannica Online
- National Public Radio
- Journal Of Lancaster General Health