Pseudomonadota is one of the largest and most diverse phyla of bacteria. This group was previously known as Proteobacteria, a name many microbiologists still use. These bacteria are found ubiquitously in various environments, including soil, water, and living in or on other organisms.
Defining Traits and Major Groups
Pseudomonadota are characterized as Gram-negative bacteria, based on their cell wall structure. They possess a thin layer of peptidoglycan situated between two membranes: an inner cytoplasmic membrane and an outer membrane. This outer membrane, mainly composed of lipopolysaccharides, distinguishes them from Gram-positive bacteria.
Pseudomonadota exhibit vast metabolic diversity. Some members are phototrophs, converting sunlight into energy, while others are heterotrophs, breaking down organic compounds, or lithotrophs, using inorganic chemicals. The phylum is organized into several classes, including Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Alphaproteobacteria often include species involved in symbiotic relationships, while Betaproteobacteria encompass a range of environmental bacteria. Gammaproteobacteria represent one of the largest classes, containing many genera with diverse roles.
Ecological Roles
Pseudomonadota play a widespread role in global ecosystems, particularly in nutrient cycling. They are involved in the nitrogen cycle, where some bacteria perform nitrogen fixation. For instance, species like Rhizobium, an Alphaproteobacterium, form symbiotic relationships with plants, converting atmospheric nitrogen gas into ammonia, a form usable by plants for growth.
Other members of this phylum are involved in denitrification, transforming nitrates and nitrites in soil back into nitrogen gas, which then re-enters the atmosphere. Pseudomonadota also function as decomposers in the carbon cycle, breaking down organic matter in soil and aquatic environments. This decomposition releases nutrients back into the ecosystem, contributing to soil fertility and supporting plant growth.
Impact on Health and Disease
Pseudomonadota have a dual impact on human and animal health, containing both beneficial and pathogenic members. Many well-known human pathogens belong to this phylum, particularly within the Gammaproteobacteria class. Examples include Salmonella, a common cause of food poisoning, and Vibrio cholerae, responsible for cholera.
Certain strains of Escherichia coli can also cause severe illnesses, such as foodborne diseases, while Helicobacter pylori is known to cause stomach ulcers. Despite these pathogenic roles, many Pseudomonadota species are beneficial or neutral residents of the human body. Harmless strains of E. coli, for example, are valuable components of the human gut microbiota, aiding in digestion. Other Pseudomonadota, like Hafnia alvei, are commensal in the human gastrointestinal tract and can even act as probiotics, potentially influencing appetite regulation.
Biotechnological and Industrial Uses
The metabolic versatility of Pseudomonadota makes them valuable resources in various biotechnological and industrial applications. Their ability to break down diverse compounds is harnessed in bioremediation efforts, where certain bacteria can degrade pollutants such as oil spills or industrial waste. This capacity helps in cleaning up contaminated environments.
Some Pseudomonadota are utilized for producing valuable compounds, including antibiotics, enzymes, and bioplastics, offering sustainable alternatives in manufacturing. Escherichia coli, a member of this phylum, serves as a significant “workhorse” in molecular biology and biotechnology due to its rapid growth and ease of genetic manipulation. This bacterium is widely used to produce various proteins through genetic engineering, notably human insulin for treating diabetes.