Microbiome

A microbiome is a complex community of microorganisms living within a specific habitat. The term comes from the Greek words "micro," meaning small, and "bios," meaning life. It is more than just a list of living things. In 1988, researchers Whipps et al. defined it as a microbial community in a well-defined habitat. This habitat has its own distinct physical and chemical properties. Therefore, the microbiome includes both the organisms and their "theatre of activity."

Scientists often distinguish this from the "microbiota." The microbiota refers only to the living members of the community. The microbiome encompasses the living members plus the environment they interact with.

Microbes within a microbiome interact through sophisticated chemical processes. One important method is called quorum sensing. This is when bacteria use small molecules to communicate with one another. This communication allows them to control cooperative activities. It helps them adapt their phenotypes, or physical traits, to their environment. For example, quorum sensing can lead to cell-cell adhesion or the formation of a biofilm. A biofilm is a structured community of microbes attached to a surface. They also use secondary metabolites to manage complex interactions. These chemicals help different species survive in highly competitive environments.

Most researchers agree on which organisms belong in a microbiome. The primary members include bacteria, archaea, fungi, algae, and small protists. There is some scientific debate regarding other elements. Some scientists argue whether to include phages, viruses, plasmids, and mobile genetic elements. These different types of organisms form a diverse microbial consortium. This consortium works together to maintain the health of their host. Whether in the ocean or on land, these interactions are vital for life.

The history of studying these tiny worlds began in the seventeenth century. Early microbiology focused on the discovery of microorganisms using primitive microscopes. Antonie van Leeuwenhoek was a pioneer in this field. He discovered bacteria, fungi, and protozoa in samples like water and dental plaque. He called these tiny organisms "animalcules." Later, Robert Koch developed the concept of pathogenicity. This explained how certain microbes cause infectious diseases in humans and animals. For a long time, the scientific focus remained on microbes that caused harm. However, we now know that only a small proportion of microbes are actually pathogenic.

Modern science has shifted toward understanding the beneficial roles of microbes. In the late nineteenth century, Martinus W. Beijerinck and Sergei Winogradsky helped start microbial ecology. They discovered that microorganisms are everywhere in natural environments. They also found that microbes can have beneficial effects on their hosts. This changed the view of microbes from simple single cells to complex assemblages. Communication and species interactions are critical to how these populations function. Today, we recognize that the overwhelming majority of microbes are essential for healthy ecosystems.

Technological breakthroughs have revolutionized how we study these communities. The discovery of DNA and the invention of PCR allowed for cultivation-independent research. This means scientists can study microbes without needing to grow them in a lab. In 1977, Carl Woese and George E. Fox introduced phylogenetic markers. They used the 16S rRNA gene to analyze microbial communities. This allowed biologists to "barcode" different types of microbes in their natural habitats. Today, high-throughput sequencing allows for the analysis of entire genomes and metagenomes. This provides a detailed look at the functional potential of whole microbial communities.

Microbiomes are found in almost every living thing on Earth. Plants host microbial communities in two main areas. The endosphere is the area inside plant tissues. The episphere is the area outside the plant tissues. These microbes are essential for plant health and food production. In the ocean, marine animal microbiomes help animals adapt to environmental changes. This is especially important due to climate-related changes in the ocean. In mammals, the gut microbiome is a key regulator of host physiology. The coevolution between hosts and microbes has helped mammals adapt to diverse lifestyles.