Adaptation and Acquisition
By Nicholas Pust | Computer Science Major
N o organism on Earth evolves faster and more frequently than bacteria. This has allowed bacteria to adapt to nearly any challenge they have faced. Bacteria are unicellular microorganisms that can adapt to changes in their environment through mutations that are either gained randomly or acquired from other bacteria (MacGowan & Macnaughton 622). With their quick multiplication and vast genetic diversity, bacteria change quickly and often (Hershberg 521). The effectiveness of the mutations of bacteria are affected by a great number of factors, including antibiotics meant to eliminate them, other microorganisms competing for resources, and the larger organisms that bacteria infect. All of these factors come together to create the active environment in which bacteria exist, which determines if the bacteria succeeds or fails. The ability for bacteria to evolve into stronger strains is dependent on adaptations caused by antibiotics, changes in the bacteria’s environment, and other organisms.
One of the main methods to combat bacterial infections are antibiotics. Antibiotics are a type of microbial drug used to halt the growth of and destroy bacteria. Selman Waksman first used the word antibiotic as a noun in 1941 to describe any small molecule made by a microbe that antagonizes the growth of other microbes (Clardy et al 1). They do this by breaking down systems vital to only bacteria cells, causing no damage to human cells in the process. Because of this, antibiotics are an incredibly effective way of dealing with bacteria, although they have no effect on fungi or viruses. The first widely distributed antibiotic was penicillin, found almost by accident by Scottish scientist Alexander Fleming. According to the Nobel Prize website, in 1928, Fleming observed that when a mold had contaminated a petri dish with bacteria in it, the mold had produced a substance that destroyed the bacteria (“Sir Alexander Fleming — Biographical”). Since this first discovery, new antibiotics have had to be created to fight newly resistant bacteria.
The ability for bacteria to become resistant to antibiotics significantly improves their effectiveness. When resistance is acquired, the antibiotics designed to neutralize the bacterial threat will not work, which can lead to sickness and death. The chance for bacteria to acquire a resistance through a mutation is determined by a wide variety of factors, including the bacteria species, antibiotic type, and environment (Martinez and Baquero 1776). All of these factors allow for bacteria to quickly become resistant to new antibiotics, which allows them to evolve into stronger strains.
There are many ways for bacteria to be unaffected by antibiotics. According to the Centers for Disease Control, there are multiple methods for bacteria to repel antibiotics. The first is for the bacteria to neutralize the antibiotic by rendering it harmless. Another method is to force the antibiotic outside of the bacteria before it can do any damage. The last method is for the bacteria to alter the outside of the cell so the antibiotic cannot attach to the bacteria it is designed to kill (“Antibiotic Resistance Questions and Answers”). These adaptations allow for the bacteria to become resistant to destruction or neutralization from the antibiotic.
Bacteria become resistant to antibiotics through mutations. A mutation is a permanent alteration in the sequence of DNA in a molecule. This results in a change in the function specified by that gene (Habibi Najafi & Pezeshki 628). Because of the incredibly large amount of replications happening in DNA at any given time, it is possible for many mutations to occur at once. While the rate of mutation would seem to be constant, according to Martinez and Baquero, “…the “mutation rate” is not a simple characteristic of a specific bacterial species-antibiotic association. On the contrary, the probability of the emergence of antibiotic-resistant mutants is a complex phenomenon” (1772). What this means is that bacterial adaptation to new antibiotics can be at times unpredictable.
Mutations aren’t the only way for bacteria to acquire antibiotic resistance. Once one bacterium is resistant, the resistance can be passed to other bacterium. According to the Centers for Disease Control, if even one bacterium acquires resistance, when an antibiotic clears out the group, that bacteria can multiply and repopulate the area (“Antibiotic Resistance Questions and Answers”). This means that when antibiotics are used, the next group of bacteria will be more resistant to the antibiotic used to eliminate the previous group. Along with being passed through inheritance, antibiotic resistance can be passed from cell to cell in the current group. MacGowan and Macnaughton write that antibiotic resistance genes are carried on mobile genetic elements (either plasmids or transposons) (622). These genetic elements can be transferred from cell to cell through several methods. These methods include conjugation, which is transfer from one cell to the other directly, transduction, which is the transfer of bacterial DNA via bacteriophages, and transformation, which is the uptake of DNA from the environment (MacGowan & Macnaughton 622). Thus, when one bacterium mutates, the resistance can be passed to through bacteria populations both “vertically,” when new generations inherit antibiotic resistance genes, and “horizontally,” when bacteria share or exchange sections of genetic material with other bacteria (“General Background: About Antibiotic Resistance”). The ability for bacteria to pass along acquired strengths allows them to adapt to nearly any situation.
It is important to remember that bacteria are living organisms, and thus live in an ecosystem along with other microbes. The success of bacteria is heavily influenced by the behaviors of the other organisms in their ecosystem. This can mean aggressive microbes that compete for resources, or other, similar bacteria strains that the current strain mutated from. Additionally, this can be seen through the need for hosts. A host is an organism that a bacteria has infected and uses to travel from one location to another, spreading along the way. These factors affect how bacteria can evolve into stronger strains.
Bacteria exist virtually everywhere. They live on all surfaces, in all regions, and in all organisms. This means that bacteria and other microbes are constantly competing against each other for finite resources. As Ghoul and Mitri state, “microbes are typically surrounded by different strains and species with whom they compete for scarce nutrients and limited space” (833). The need for space to multiply means that when an antibiotic clears out a strain of bacteria, a new and resistant strain has plenty of room to fill (“About Antimicrobial Resistance”). The battle between microbes leads to them employing various techniques to eliminate competition. They fight in two ways: either indirectly through exploitative competition, which is where they consume resources necessary for other microbes to survive, and through interference competition, which is where they damage other cells directly. While under the strain of competition, microbes have evolved into both of these strategies, such as rapid growth to take up resources for exploitative competition and the evolution of aggressive phenotypes for interference competition (Ghoul & Mitri 842). While it might seem that this battle would continue indefinitely, “… evidence suggests that, over time, competition dies down locally, often leading to stable coexistence of genetically distinct lineages” (833). This leads to a local reduction in diversity and an increase in ecological stability. There are three ways for an ecosystem to achieve ecological stability: the extinction of less competitive strains, the coexistence of strains through the consumption of different resources, and the separation of strains into different spatial niches (840). To conclude, bacteria exist in an environment where strains often don’t thrive and can go extinct. The success of bacteria is dependent on their ability to evolve into ways to compete with other microbes.
“Microbes are typically surrounded by different strains and species with whom they compete for scarce nutrients and limited space” (Ghoul and Mitri 833).
When a new strain of bacteria evolves from an old one, the old strain has an effect on the new one. Specifically, as Hartfield and Alizon write, “…a proportion of the host susceptible population is removed as the first strain spreads” (Hartfield & Alizon E105). Work by Hartfield and Alizon suggests that the first strain from an adaptive mutation will spread quickly, but as a second strain appears later on than the first, it has a lower chance of emerging due to fewer susceptible individuals present (E107). The decrease in susceptible individuals can be from hosts dying, space in the host’s body being filled with the first strain, not allowing a second strain to thrive, or a resistance developed by the host’s body after the first infection. This means that the success of future strains of bacteria are highly dependent on the strains that come before.
Bacteria are microscopic organisms that rely on other organisms for travel. They can spread from human to human through sneezes and coughs, which eject the bacteria into the air to infect other humans. Additionally, bacteria can exist outside of the body on common objects, allowing them to infiltrate the body when people touch these objects (“Understand How Infectious Diseases Spread”). Understandably, the more potential hosts in an area, the faster a bacteria can spread through that population. A model from Hartfield and Alizon suggests that there is a minimum susceptible population needed for an original pathogen strain to mutate into a faster-spreading strain. Below this proportion, emergence of a new strain is impossible (Hartfield & Alizon E111). Ultimately, the ability for a bacteria to spread far is heavily influenced by the number of susceptible hosts in a population.
Bacteria are not restrained to only one population, however. It is possible for bacteria to mutate into the ability to “jump” to a new species. Diseases transferred from other species are the most significant cause of disease in humans (Benavides et al 774). According to research by Woolhouse, Haydon, and Anita, there are three steps needed for a pathogen to cross to a new species. First, the pathogen needs to be exposed to the new host species (239). This commonly happens with domestic animals in close proximity to humans, such as pigs and cows. The second step is for the pathogen to be able to infect the new host. For this to be possible, both of them need to be “compatible” with one another (240). The range of compatibility for pathogens is incredibly high, meaning that there could be a high chance for animal to human contamination for one bacteria, but it could be impossible for another. The third and final step is for the pathogen to be able to travel sufficiently among the new host population (241). If a new bacteria had no way to travel among humans, it would not succeed with this new strain. Overall, the ability for a bacteria to mutate to infect a new species is incredibly powerful.
Bacteria exist in a constantly shifting environment, and they adapt to changes that occur in it. They fight against other microbes for superiority in these micro-ecosystems, resulting in mutations that allow them to gain the upper hand for resources and space (Ghoul & Mitri 833). Bacteria are also dependent on previous strains, performing well or poorly depending on the last (Hartfield & Alizon E105). Bacteria, being microorganisms, depend on their infected hosts to spread, and how well they spread depends on how many potential hosts they have (“Understand How Infectious Diseases Spread”). Finally, bacteria possess the ability to contaminate other species, allowing incredible expansion (Benavides et al.). All of these factors result in bacteria mutating to fit their needs, resulting in a highly adaptable organism that can evolve into stronger strains.
The ability for bacteria to evolve into stronger strains is dependent on adaptations caused by antibiotics, changes in the bacteria’s environment, and other organisms. Bacteria are unicellular organisms capable of adapting to changing environments through mutations. These changes can be found in antibiotic resistances, techniques against competing microbes in an ecosystem, mutations from previous strains, and “jumps” to other species. However, the success of a bacteria is not dependent solely on adaptations. There are various external factors that affect the success of a bacteria. These factors include previous strains, potential hosts, and failures in competitive ecosystems. Ultimately, the success of bacteria is determined by how they adapt to these challenges. To conclude, bacteria are highly adaptable microorganisms that can evolve into stronger strains through mutations caused by changes in their environment.
Works Cited:
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ABOUT THE AUTHOR:
Nicholas Pust, a freshman from Cottage Grove, Minn., is a computer science major at Bethel University. He hopes to become a computer programmer in the future. Nicholas enjoys reading, swimming, and spending time with friends.
