Bacteria

Bacteria are ubiquitous, single-celled microorganisms that belong to the domain of prokaryotes. They are among the most successful life forms on Earth, appearing about 4 billion years ago. These organisms are found in almost every habitat imaginable. They thrive in soil, water, and the air. Some even live in extreme environments like acidic hot springs or radioactive waste.

Bacteria are essential to the planet's survival. They drive the nutrient cycle by recycling dead matter through a process called putrefaction. They also perform nitrogen fixation, which moves nitrogen from the atmosphere into the soil.

At a cellular level, bacteria are structurally distinct from eukaryotes, which include plants and animals. A bacterial cell is surrounded by a cell membrane made of phospholipids. This membrane acts as a barrier to protect essential proteins and nutrients. Unlike eukaryotic cells, bacteria do not have a nucleus to house their genetic material. Instead, they contain circular chromosomes. They also lack membrane-bound organelles, which are the specialized internal compartments found in larger cells.

This simple structure allows them to remain efficient and highly adaptable.

Bacteria display a massive variety of shapes and arrangements. Most species are categorized by their physical form. Spherical bacteria are called cocci, while rod-shaped bacteria are known as bacilli. Some appear as curved rods called vibrio, or as spirals known as spirilla and spirochaetes.

These shapes are determined by the cell wall and the cytoskeleton. The specific shape helps a bacterium acquire nutrients or escape from predators. While most are microscopic, some are surprisingly large. For example, *Thiomargarita magnifica* can reach 2 centimeters in length. This is 50 times larger than typical bacteria.

Bacteria do not always live as solitary cells. Many species form complex groups or patterns. Some form pairs called diploids, while others form long chains or grape-like clusters. Certain bacteria, such as myxobacteria, use a process called quorum sensing to communicate. When they sense they are starving, they migrate together to form fruiting bodies. These structures can contain up to 100,000 cells that perform different tasks.

Many bacteria also create biofilms. A biofilm is a dense aggregation of cells attached to a surface. These can grow up to half a meter deep. Biofilms protect bacteria, making them much harder to kill with medicine.

Historically, our understanding of bacteria has changed significantly. In the past, scientists incorrectly classified them as plants called Schizomycetes. We now know they are prokaryotes. In the 1990s, researchers discovered that prokaryotes actually consist of two distinct groups. These are the domains Bacteria and Archaea. While they look similar, they have deep genetic differences. For example, bacteria use ester-linked lipids in their membranes. They also use formylmethionine to start protein synthesis.

Humanity has a complex relationship with these organisms. Humans carry between 10^13 and 10^14 bacteria on and in their bodies. Most of these live in the gut and are either harmless or beneficial. However, some bacteria are pathogenic, meaning they cause infectious diseases. These include cholera, anthrax, tuberculosis, and the bubonic plague.

To fight these, we use antibiotics. However, the use of antibiotics in medicine and farming has led to the rise of antibiotic resistance.

Beyond health, bacteria are vital to global industry and ecology. They are used in sewage treatment and the breakdown of oil spills. In the food industry, fermentation by bacteria produces cheese and yogurt. In mining, a process called biomining uses bacteria to recover metals like gold and copper. They even help provide oxygen; bacteria in the oceans provide up to 50% of the oxygen humans breathe.

Despite their importance, we have only fully studied about 2% of all bacterial species. Much of the microbial world remains a vast, unexplored frontier.