Sign up to access the complete lesson and track your progress!
Unlock This CourseBacteria are some of the fastest-evolving organisms on Earth. Unlike humans who might take decades to reproduce, bacteria can divide every 20 minutes under ideal conditions. This means they can evolve incredibly quickly, sometimes developing new traits in just days or weeks. Understanding how bacterial populations change is crucial for medicine, agriculture and our understanding of evolution itself.
Key Definitions:
Bacteria reproduce through binary fission - they simply split in two. With generation times as short as 20 minutes, a single bacterium can become over a million bacteria in just 7 hours. Each time they reproduce, there's a chance for mutations to occur, creating the raw material for evolution.
Bacterial evolution follows the same basic principles as evolution in all organisms, but it happens much faster. The process involves three key steps: variation through mutation, selection pressure from the environment and differential reproduction of successful variants.
Every time a bacterium reproduces, there's a small chance that copying errors will occur in its DNA. Most mutations are neutral or harmful, but occasionally one provides an advantage. In a population of millions of bacteria, beneficial mutations are almost guaranteed to appear.
Single DNA letter changes that might alter protein function, potentially giving resistance to drugs or toxins.
When genes are copied multiple times, providing extra copies that can evolve new functions.
Bacteria can share genes directly with other bacteria, even different species, spreading beneficial traits quickly.
The environment constantly challenges bacterial populations. These pressures determine which bacteria survive and reproduce. Common selection pressures include antibiotics, temperature changes, pH levels, nutrient availability and competition from other microorganisms.
Methicillin-resistant Staphylococcus aureus (MRSA) evolved from regular Staph aureus bacteria. When penicillin was first used in the 1940s, it killed almost all Staph bacteria. However, a few had mutations that made them slightly resistant. These survived, reproduced and passed on their resistance genes. Over decades, the bacteria evolved stronger and stronger resistance, eventually becoming immune to methicillin and many other antibiotics.
Antibiotic resistance is perhaps the most important example of bacterial evolution affecting human society today. When antibiotics are used, they create a strong selection pressure that favours resistant bacteria.
Imagine a bacterial infection with millions of bacteria. Most are killed by antibiotics, but a few have mutations that help them survive. These survivors reproduce rapidly in the absence of competition, creating a new population that's mostly resistant to the antibiotic.
Antibiotic resistance can develop in just days to weeks. In hospitals, resistant strains can appear within a single patient's treatment course, especially if antibiotics are not taken properly or treatment is stopped early.
Different environments create different selection pressures, leading bacteria to evolve in various directions. Understanding these factors helps us predict and manage bacterial evolution.
Bacteria living in extreme environments, like hot springs or acidic mine drainage, have evolved special proteins and cellular mechanisms. These adaptations often involve multiple mutations working together to create heat-stable or acid-resistant enzymes.
Thermophilic bacteria have evolved proteins that don't denature at high temperatures, allowing them to thrive in hot springs.
Acidophilic bacteria pump out excess hydrogen ions and have acid-resistant cell walls to survive in extremely acidic conditions.
Psychrophilic bacteria produce antifreeze proteins and flexible membrane lipids to function in freezing temperatures.
Since 1988, scientist Richard Lenski has been growing E. coli bacteria in his lab, tracking their evolution over more than 75,000 generations. The bacteria have evolved larger cell sizes, faster growth rates and even the ability to eat citrate - something E. coli normally cannot do. This experiment shows how bacteria can evolve entirely new capabilities given enough time and the right conditions.
Understanding bacterial evolution is crucial for developing effective medical treatments and preventing the spread of dangerous resistant strains.
Medical professionals now use several strategies based on evolutionary principles to slow the development of resistance. These include using combination therapies, rotating different antibiotics and ensuring patients complete their full course of treatment.
Using multiple antibiotics simultaneously makes it much harder for bacteria to evolve resistance to all drugs at once. The probability of developing multiple resistances simultaneously is extremely low.
As bacteria continue to evolve, we must develop new approaches to stay ahead. These include developing new types of antibiotics, using bacteriophages (viruses that kill bacteria) and creating drugs that target bacterial evolution itself.
Scientists use bacterial evolution in beneficial ways, from producing medicines to cleaning up pollution. By understanding how to direct bacterial evolution, we can harness these rapid changes for human benefit.
Scientists can guide bacterial evolution by controlling selection pressures in the laboratory. This technique is used to develop bacteria that produce medicines, break down pollutants, or manufacture useful chemicals more efficiently.
In 2016, scientists discovered bacteria that had evolved the ability to break down PET plastic - the type used in bottles. These bacteria likely evolved this ability in response to the increasing amount of plastic waste in their environment. Researchers are now working to enhance this ability through directed evolution to help solve the global plastic pollution problem.