Bacteria first evolved over 3.5 billion years ago and have adapted to their environments over time. They diverged from archaea early in their evolution. Bacteria can be found in diverse environments due to their ability to adapt through mutations and genetic exchange between organisms, allowing them to evolve rapidly in response to changes like the emergence of antibiotics. Mobile genetic elements like transposons help accelerate bacterial evolution by spreading genes within and between species.

1. 1Amjad Khan Afridi, 25th
October, 2020
Evolution Of Bacteria
Bacteria have existed from very early in the history of life on Earth. Bacteria fossils discovered
in rocks date from at least the Devonian Period (419.2 million to 358.9 million years ago), and
there are convincing arguments that bacteria have been present since early Precambrian time,
about 3.5 billion years ago. Bacteria were widespread on Earth at least since the latter part of the
Paleoproterozoic, roughly 1.8 billion years ago, when oxygen appeared in the atmosphere as a
result of the action of the cyanobacteria. Bacteria have thus had plenty of time to adapt to
their environments and to have given rise to numerous descendant forms.
The nature of the original predecessor involved in the origin of life is subject to
considerable speculation. It has been suggested that the original cell might have used RNA as its
genetic material, since investigations have shown that RNA molecules can have numerous
catalytic functions. The Bacteria and Archaea diverged from their common precursor very early
in this time period. The two types of prokaryotes tend to inhabit different types of environments
and give rise to new species at different rates. Many Archaea prefer high-temperature niches.
One major branch of the archaeal tree consists only of thermophilic species, and many of the
methanogens in another major branch can grow at high temperatures. In contrast, no
major eubacterial branch consists solely of thermophiles. Both Bacteria and Archaea contain
members that are able to grow at very high temperatures, as well as other species that are able to
grow at low temperatures. Another prominent difference is that bacteria have widely adapted to
aerobic conditions, whereas many archaea are obligate anaerobes. No archaea are obligately
photosynthetic. Perhaps the archaea are a more primitive type of organism with an impaired
genetic response to changing environmental conditions. A limited ability to adapt to new
situations could restrict the archaea to harsh environments, where there is less competition from
other life-forms.

2. 2Amjad Khan Afridi, 25th
October, 2020
Organisms must evolve or adapt to changing environments, and it is clear that mutations,
which are changes in the sequence of nucleotides in an organism’s DNA, occur constantly in all
organisms. The changes in DNA sequence might result in changes in the amino acid sequence of
the protein that is encoded by that stretch of DNA. As a result, the altered protein might be either
better-suited or less well-suited for function under the prevailing conditions. Although many
nucleotide changes that can occur in DNA have no effect on the fitness of the cell, if the
nucleotide change enhances the growth of that cell even by a small degree, then the mutant form
would be able to increase its relative numbers in the population. If the nucleotide change retards
the growth of the cell, however, then the mutant form would be outgrown by the other cells and
lost.
The ability to transfer genetic information between organisms is a major factor
in adaptation to changes in environment. The exchange of DNA is an essential part of the life

3. 3Amjad Khan Afridi, 25th
October, 2020
cycle of higher eukaryotic organisms and can occur in all eukaryotes. Genetic exchange occurs
throughout the bacterial world as well, and, although the amount of DNA that is transferred is
small, this transfer can occur between distantly related organisms. Genes carried on plasmids can
find their way onto the bacterial chromosome and become a stable part of the bacterium’s
inheritance. Organisms usually possess mobile genetic elements called transposons that can
rearrange the order and presence of any genes on the chromosome. Transposons may play a role
in helping to accelerate the pace of evolution.
Many examples of the rapid evolution of bacteria are available. Before the
1940s, antibiotics were not used in medical practice. When antibiotics did eventually come into
use, the majority of pathogenic bacteria were sensitive to them. Since then, however, bacterial
resistance to one or more antibiotics has increased to the point that previously effective
antibiotics are no longer useful against certain types of bacteria. Most examples of antibiotic
resistance in pathogenic bacteria are not the result of a mutation that alters the protein that the
antibiotic attacks, although this mechanism can occur. Instead, antibiotic resistance often
involves the production by the bacterium of enzymes that alter the antibiotic and render it
inactive. A major factor in the spread of antibiotic resistance is transmissible plasmids, which
carry the genes for the drug-inactivating enzymes from one bacterial species to another.
Although the original source of the gene for these enzymes is not known, mobile genetic
elements (transposons) may have played a role in their appearance and may also allow their
transfer to other bacterial types.