Overview
Eubacteria, often simply called bacteria, are prokaryotic microorganisms characterised by the presence of a peptidoglycan cell wall, lack of a membrane‑bound nucleus and reproduction by binary fission. They form one of the major domains of life distinct from Archaea and Eukarya.
Explanation
In contemporary taxonomy the domain Bacteria encompasses the organisms formerly called “eubacteria” to distinguish them from archaebacteria. These single‑celled prokaryotes have a circular chromosome located in a nucleoid, ribosomes resembling those of mitochondria, and no internal membrane‑bound organelles. The cell wall contains peptidoglycan, the thickness and composition of which form the basis of the Gram stain classification into Gram‑positive and Gram‑negative bacteria. Many possess flagella for motility or pili for adhesion and genetic exchange. Metabolic diversity is a hallmark: some bacteria are photoautotrophs, such as cyanobacteria that perform oxygenic photosynthesis; others are chemoautotrophs or heterotrophs capable of utilising a wide range of organic and inorganic substrates. Horizontal gene transfer via transformation, transduction and conjugation contributes to genetic diversity. Bacteria inhabit nearly every environment on Earth, from soil and water to extreme niches such as hot springs and deep‑sea vents. While many species are harmless or beneficial symbionts, others are significant pathogens of humans, animals and plants. Molecular phylogeny based on 16S rRNA sequences has reorganised bacterial taxonomy into numerous phyla and classes.
Examples and significance
Common bacterial species include Escherichia coli, a Gram‑negative facultative anaerobe that resides in the intestinal tract; Bacillus subtilis, a Gram‑positive soil bacterium known for endospore formation; and Staphylococcus aureus, a Gram‑positive coccus associated with skin and wound infections. Cyanobacteria such as Prochlorococcus and Anabaena are important primary producers in aquatic ecosystems and contribute to nitrogen fixation. Nitrogen‑fixing rhizobia form symbiotic relationships with legumes, converting atmospheric nitrogen into ammonia. On the other hand, pathogenic eubacteria include Mycobacterium tuberculosis, Vibrio cholerae and Clostridium tetani. Understanding bacterial physiology and genetics underlies advances in medicine, biotechnology and environmental science.
Eubacteria represent an ancient and diverse lineage of prokaryotes that have adapted to virtually every habitat. Their structural simplicity belies vast metabolic versatility and ecological importance, making them central to nutrient cycling, symbiosis and disease.
Related Terms: Bacteria, Prokaryote, Archaea, Gram-positive, Gram-negative