Evolution of bacteria

Bacteria are prokaryotic microorganisms that have shaped the history of life on Earth. These simple cells measure between 0.5 and 20 micrometers in size. They can take on several distinct shapes, including bacilli, spirilli, or cocci. While they are much simpler than eukaryotic cells, they still share some features like a cell membrane, cytoplasm, and ribosomes. However, bacteria have unique structures such as a cell wall, flagella, and a nucleoid.

These tiny organisms are incredibly resilient. They inhabit diverse environments, ranging from freezing glacial rocks to extreme hydrothermal vents on the ocean floor.

Bacterial evolution follows the principles of natural selection. This process occurs when beneficial adaptations are passed to future generations. Most bacteria reproduce through binary fission, which is a form of asexual reproduction. In this process, a parent cell creates a genetically identical daughter cell. Because these offspring are clones, bacteria can be vulnerable to environmental changes. To overcome this, they share genetic information through transduction, transformation, or conjugation.

These methods allow for new physical and genetic adaptations. Because some bacteria can reproduce in as little as 20 minutes, they can evolve very quickly. This rapid adaptation has led to modern challenges like antibiotic resistant bacteria.

The earliest history of bacteria is found in the Precambrian time. Scientists use gene sequencing of bacterial nucleoids to reconstruct their phylogeny, or family tree. Evidence of early life also comes from permineralized microfossils. In the Australian Apex Chert, researchers found microfossils dating back roughly 3.5 billion years.

These fossils suggest that an organism similar to the phylum Thermotogota was a recent common ancestor of modern bacteria. Thermotogota are typically anaerobic, meaning they do not require oxygen. They are often thermophilic or hyperthermophilic, meaning they thrive in high temperatures. They can live near hydrothermal vents where temperatures reach between 55 and 95 °C.

Within the Thermotogota phylum, there have been several major evolutionary splits. The first major divergence occurred between the families Thermotogaceae and Fervidobacteriaceae. Later, the Thermotogaceae family diverged into the genera Thermotoga and Pseudothermotoga. The genus Thermotoga includes many hyperthermophiles found today. A unique feature of this genus is an outer membrane called a "toga." One known species is Thermotoga neapolitana.

Some scientists believe the Thermotogales lineage evolved between 3.2 and 3.5 billion years ago.

A massive shift in Earth's atmosphere was caused by the evolution of cyanobacteria. These are photosynthetic bacteria that evolved between 2.3 and 2.7 billion years ago. They use sunlight to drive metabolic processes, which removes carbon dioxide from the atmosphere. As a byproduct of this process, they release oxygen.

Chemical and isotopic analysis of ancient rocks shows that oxygen appeared in the oceans by the Siderian period, roughly 2.45 billion years ago. This rise in oxygen likely led to the Great Oxygenation Event about 2.3 billion years ago. This event fundamentally altered the Earth's ecosystem.

Cyanobacteria are highly successful and live in many places, including oceans, freshwater, soil, and even arctic rock. They often form motile filaments called hormogonia, which allow them to colonize new areas. Genetic sequencing shows that cyanobacteria evolved from a non-photosynthetic common ancestor. Their closest relatives, Melainabacteria and Sericytochromatia, do not possess the genes required for photosynthesis.

Beyond their role in history, cyanobacteria are important to the pharmaceutical and agricultural industries. They can produce bioactive compounds with antibacterial, anti-fungal, antiviral, and anti-algal properties.

The rise of atmospheric oxygen also allowed for the evolution of the phylum Pseudomonadota. This group evolved approximately 1.5 billion years ago during the Paleoproterozoic era. Today, Pseudomonadota is a very diverse group of microorganisms. It includes many free-living microbes, various pathogens, and nitrogen fixing bacteria.

While microfossils provide clues, some scientists argue that the lack of clear morphology in these fossils makes it difficult to build a perfect timeline. Nevertheless, new technological developments continue to reveal more about how these tiny life forms changed our world.