Evolutionary Microbiology

Introduction

Evolution has been a very controversial topic in terms of science and religion however with regard to prokaryotes there is no speculation about micro-organisms being able to evolve. In regard to micro-organisms the term evolution has a different meaning compared to eukaryotes. Prokaryote evolution refers to the adaptation of a micro-organism to the environment it exists in rather than the eukaryote evolution which states that the organism becomes a new species altogether. With prokaryotes there evolution can be analysed by many modern techniques that target the genome of the bacterium and compares it to other bacteria. However unlike eukaryotes that have fossil record that show species that existed millions of years ago,prokaryotes are not able to form fossils due to their soft bodies but stromalites are an exception to this. There are 3 distinct types of genetic changes that can occur to indicate evolution in a cell these are: Nucleotide changes, sequence changes and Horizontal Gene Transfer.

An example of adaptation can be seen with the different E.coli strains, K-12 and O157:H7, K-12 are relatively safe and used in most laboratories however O157:H7 is pathogenic and is responsible for food poisoning, they are not different species but they occur with different adaptations and this can be seen with regard to genome size and using an evolutionary chronometer. Evolution in bacteria can occur for many different reasons, the most common is due to use of antibiotics and environmental stress that can force the organism to change to its environment. Time plays a great role in evolution of the organism also. The micro-organisms have many different methods in order to adapt to the environment and some of these methods are quite advanced.

Method of measuring evolution

Evolution is measured by noticing how similar the strains are or how similar the species are. The most useful method for determining evolution is by using genetic material and creating a comparison. An evolutionary chronometer is generally used to determine the separation of two different genetic sequences, the evolutionary chronometer can be an amino acid or a nucleotide. An evolutionary chronometer has to have the following characteristics:

Universally distributed.

Functionally homologous.

Sequence should be changed with relation to evolutionary distance measured.

It's function must be conserved.

The sequence that is chosen for study depends on the evolutionary distance of the organisms being studied, if the organisms are of the same species then a fast-evolving gene would be chosen to show evolution however if it is two different species then a slow-evolving gene would be used so that there is a comparison between the two. A bacterial cell has a specific set of genes that are called evolutionary genes and are separate from housekeeping genes and other genes, these evolutinary genes occur in two sets. The first set is used for generating a genetic variation in the micro-organisms and the other set of genes is used for modulating the frequency at which the genetic variation occurs. These evolutionary genes might be fine-tuned over a long amount of time making them specific to a certain purpose in order to benefit the micro-organism. The usage of an evolutionary chronometer is not perfectly accurate because a genetic change can occur in a different gene and scientists are unable to pick up on this genetic change unless it is indicated by a phenotypic change in the micro-organism.

What effects does evolution have on the organism?

Prokaryotes have many different factors that can affect evolution whether forced or natural these evolutions are essential for survival. Evolution in an organism can give them an "edge" in terms of survival such as the production of an enzyme that can utilise a substrate that other organisms cannot or the production of antibiotics to inhibit other competing organisms. The evolution can also cause morphological diversity but not in the case that the bacteria becomes a different species, with regard to sexual reproduction the sex pilus can be formed when conjugation occurs.

Evolution is a positive effect and can cause the bacterial cell to become better and more adapted for the environment. The environment that the bacteria exist in has the greatest affect on the evolution such in the case of motile bacteria that the flagella are used in moist environments to allow movement to nutrients, this adaptation is only good for moist environments whereas on solid surfaces the pili are used for twitching motility, this is an indication of how the environment can affect the motility organs of the bacterial cell.

Evolution is almost a necessity for all bacteria because it allows greater survival especially in harsh environments and the usage of many antimicrobial products also force the bacteria to evolve. The bacteria have many ways of evolving and this is essentially a change in the genetic code to let them become more efficient.

Why is evolution important to be studied?

Evolution is important to be studied in order to understand how certain abilities are acquired by an organism and it will also give more understanding on how to combat pathogenic bacteria. Evolution can further be understood to find out how bacteria interact with different species and the transfer of genes between many populations. Using this information the gene transfer can be interrupted preventing the transfer of genes and the possible creation of a superbug.

With regard to extreme drug resistant tuberculosis(XDR-TB) this method of understanding gene transfer and evolution of microbes can indicate how the bacterium was able to become so resistant and may also pinpoint a weak point in the bacterium that antibiotics can target. The evolution can also indicate changes in the environment that the bacteria was present in with regard to the initial adaptations and the adaptations that have occurred due to a change in the environment. Evolution is important to be studied to give a clearer understanding about why the bacteria inhabit certain areas according to their genes and also the relationships that they form with other organisms and the environment in order to survive. A genetic variation can occur as a result natural selection combined with genetic variations and also in certain cases mutations can cause evolution in micro-organsims. However mutation should not be taken into account as a great factor for evolution because in very few cases the cell is able to acquire an advantageous

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