Chlamydiota

Some tiny germs live inside other living things.

These germs are very small. They can be as small as a virus. They must live inside a host cell to grow.

Some of these germs can make people sick. They can cause a lung sickness. They can also hurt your eyes.

Scientists found new ones in the deep ocean. These live on the ocean floor. We do not know much about them yet.

These tiny germs are very interesting to study.

Chlamydiota are a group of tiny bacteria. They are very small. Some are as small as a virus. Most of these bacteria must live inside other cells. We call these cells host cells. These bacteria cannot grow on their own. They need a host to make more of themselves.

These germs have a special way of life. They have two main forms. One form is called an elementary body. This form is like a tough spore. It helps them survive outside a cell. The other form is called a reticulate body. This form lives inside the host cell. It is where the bacteria grow and multiply.

Some Chlamydiota can make people sick. One kind causes a lung sickness called pneumonia. Another kind causes an infection called chlamydia. In the United States, chlamydia is a very common infection. About 2.86 million cases are reported every year. Scientists also found new kinds of Chlamydiota on the ocean floor in 2020. We are still learning about them.

Tiny bacteria seen through a powerful microscope.

How scientists look at these germs in a lab.

Chlamydiota is a group of tiny bacteria that live in many different places. Some of these bacteria live in the ocean on the sea floor. Others live inside larger living things like animals or humans. Many of the Chlamydiota we know must live inside a host cell to survive. These bacteria are very small, sometimes even smaller than a virus. They are shaped like little ovals. Some species can cause sickness in people, such as pneumonia. Another type causes an infection called chlamydia. In the United States, about 2.86 million chlamydia infections are reported every year.

These bacteria have a very special way of growing. They use a two-step life cycle to survive and spread. First, they exist as an elementary body. This form is tough and acts like a spore to survive outside a cell. Once they find a host cell, they change into a reticulate body. This second form lives inside the cell and is where the bacteria actually grow. They stay in this active form while they are inside the host. Because they need a host to grow, scientists cannot grow them in a simple lab dish. They must be grown while they are still inside living cells.

Humans have known about these bacteria for a very long time. Ancient Egyptian and Chinese writings describe eye diseases that look like chlamydia. In 1907, scientists Halberstaedter and von Prowazek gave a modern description of these organisms. Later, in the late 1920s and early 1930s, scientists grew them in egg yolks during a lung sickness outbreak. The name "chlamydia" first appeared in books in 1945. It comes from a word meaning a cloak. In 1956, Tang Fei-fan was the first to grow Chlamydia trachomatis. However, people did not realize they were bacteria until much later.

Scientists have learned many new things about how these bacteria are built. For a long time, they could not find a material called peptidoglycan in their cell walls. This material is usually very important for other bacteria. In 2013, researchers found it in a species called Protochlamydia amoebophila. In 2014, they found it in the human pathogen Chlamydia trachomatis too. They discovered it does not make a full shell around the cell. Instead, it makes a thin ring during cell division. This happens because a protein called MreB takes over a different job.

These bacteria are part of a very old family tree. They split away from other bacteria about one billion years ago. This makes them a unique group in the history of life. Scientists study their DNA to see how they are related to other things. Some studies suggest they might be related to cyanobacteria, which are tiny organisms that help plants grow. Other evidence shows they are closely related to a group called Verrucomicrobiota. In 2020, scientists found even more new types of Chlamydiota deep in the ocean. We are still discovering how these tiny organisms fit into our world.

Chlamydiota is a diverse phylum of bacteria that includes many different types of organisms. Some members are pathogens that cause disease in humans and animals. Others are symbionts that live within ubiquitous protozoa. In 2020, scientists discovered many new Chlamydiota living in ocean-floor environments. It is not yet known if all of these deep-sea forms require a host to survive. Most Chlamydiota known to science are obligate intracellular bacteria. This means they must live inside the cells of a host to complete their life cycle.

These bacteria follow a unique biphasic developmental cycle to survive and multiply. When they are outside of a host cell, they exist as elementary bodies. These are infectious, spore-like forms that possess a tough cell wall made of a protein network. Once they enter a host cell, they transform into reticulate bodies. The reticulate body is a metabolically active form that allows the bacteria to grow and replicate. They usually live within an inclusion body or a vacuole inside the host. Because they depend entirely on the host for replication, they cannot be grown in standard bacterial culture media. Scientists must isolate them while they are still inside living host cells.

Research into the cell walls of Chlamydiota has revealed surprising biological details. For a long time, scientists could not find peptidoglycan, a common bacterial material, in their cell walls. However, studies in 2013 showed that Protochlamydia amoebophila has a sacculus, or protective shell, made of peptidoglycan. In 2014, researchers found that the human pathogen Chlamydia trachomatis also contains peptidoglycan during its intracellular stage. Unlike most bacteria, Chlamydiota do not use peptidoglycan to make a full shell around the entire cell. Instead, they produce a thin ring of peptidoglycan down the middle during cell division. A protein called MreB controls this ring production, taking over the role that the FtsZ protein usually performs in other bacteria. This explains why penicillin is bacteriostatic, meaning it stops growth, rather than bacteriocidal, which kills the bacteria.

Human history with these organisms stretches back to ancient times. Manuscripts from ancient China and Egypt describe eye diseases that match Chlamydial symptoms. A modern scientific description was provided by Halberstaedter and von Prowazek in 1907. During a pneumonitis outbreak in the late 1920s and early 1930s, scientists successfully isolated Chlamydial strains using the yolk sacs of embryonating eggs. The name "chlamydia," which means "cloak," first appeared in scientific literature in 1945. In 1956, Tang Fei-fan first cultured Chlamydia trachomatis, though it was not yet recognized as a bacterium. The group was officially recognized as bacteria in 1966, and the genus Chlamydia was validated.

Chlamydiota are significant in public health due to the diseases they cause. Chlamydia trachomatis is a major human pathogen that causes both trachoma and sexually transmitted infections. In the United States, chlamydia is the most common bacterial sexually transmitted infection, with 2.86 million infections reported annually. Another important species is Chlamydia pneumoniae, which causes a type of pneumonia. Chlamydophila psittaci is also a known human pathogen that causes psittacosis. Because of their unique intracellular life cycle, doctors can use DNA analysis to diagnose these infections.

The taxonomy of Chlamydiota is complex and continues to evolve with new genetic data. The phylum is divided into two orders: Chlamydiales and Parachlamydiales. There are nine families within a single class called Chlamydiia. Four of these families are validly named: Chlamydiaceae, Parachlamydiaceae, Simkaniaceae, and Waddliaceae. Other families, such as Clavichlamydiaceae and Rhabdochlamydiaceae, are currently described. Scientists distinguish these groups using molecular signatures like conserved indels (CSIs) and conserved proteins (CSPs). These unique genetic markers help researchers understand the shared ancestry within each order.

Evolutionarily, Chlamydiota are a very ancient group. They separated from other bacterial lineages approximately one billion years ago. This long history is reflected in their unique genetic makeup. Some scientists once believed Chlamydiota shared a common ancestor with cyanobacteria, the group that includes the ancestors of plant chloroplasts. A 2004 study found that 4% to 11% of certain Chlamydiota genes were similar to cyanobacterial and plant genes. However, other evidence suggests they may be more closely related to the Verrucomicrobiota. This makes the evolutionary history of Chlamydiota a major subject of scientific study.