domainsBacteria

The domain Bacteria comprises a vast and diverse group of unicellular prokaryotes. It is one of the three domains of life in the three-domain system, alongside Archaea and Eukarya. Members are found in virtually every habitat on Earth and play essential roles in ecosystems, industry, and health.

Cellular and molecular characteristics: Most bacteria have cell walls containing peptidoglycan, though some lack it. They typically lack a membrane-bound nucleus and other organelles. They possess circular chromosomes, 70S ribosomes, and often plasmids. Many exhibit diverse morphologies, including cocci, bacilli, and spirilla. Reproduction is mainly by binary fission, and some form spores for survival. Metabolism is highly diverse, including photosynthesis in cyanobacteria, lithotrophy, and heterotrophy. They utilize a wide range of energy and carbon sources, and gene transfer occurs through transformation, transduction, and conjugation, contributing to rapid adaptation.

Ecology, diversity, and importance: The domain Bacteria includes numerous phyla such as Proteobacteria, Firmicutes, Actinobacteria, Bacteroidota, Cyanobacteria, and Spirochaetes. They inhabit soil, water, air, and living organisms, including extreme environments. They drive nutrient cycles—carbon, nitrogen, and sulfur—and some fix atmospheric nitrogen. In humans and other animals, they form microbiomes in the gut and on the skin, aid digestion, and support immunity. Pathogenic species cause diseases, including Mycobacterium tuberculosis, Escherichia coli pathovars, and Staphylococcus aureus. Industrially, bacteria are used in fermentation, biotechnology, and the production of enzymes, antibiotics, and biofuels.

Taxonomy and ongoing study: Classification within Bacteria relies on molecular data, especially 16S rRNA gene sequences and whole-genome analyses. Taxonomic frameworks are continually revised, with new phyla and reassignments emerging as data improve. The domain Bacteria is distinct from Archaea, reflecting deep genetic and biochemical differences.