Bacteria
Bacteria are single-celled prokaryotic microorganisms that lack a membrane-bound nucleus and reproduce primarily by binary fission. They are among the most abundant life forms on Earth, inhabiting nearly every environment including soil, water, and the human body. Bacteria play essential roles in nutrient cycling, decomposition, and digestion, and certain species cause infectious diseases while others are harnessed in biotechnology and food production.
Comparison of Major Bacterial Shapes and Representative Species
| Shape | Name | Example Species | Associated Disease |
|---|---|---|---|
| Spherical | Coccus | Staphylococcus aureus | Skin infections |
| Rod-shaped | Bacillus | Escherichia coli | Urinary tract infection |
| Spiral | Spirillum | Helicobacter pylori | Gastric ulcers |
| Comma-shaped | Vibrio | Vibrio cholerae | Cholera |
| Filamentous | Actinomycetes | Streptomyces griseus | None (antibiotic producer) |
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Related Terms
Archaea
Archaea are a domain of single-celled prokaryotic microorganisms that are distinct from bacteria despite lacking a membrane-bound nucleus. They are notable for inhabiting extreme environments such as hot springs, salt lakes, and deep-sea hydrothermal vents, earning many members the label "extremophiles." Archaea share some features with eukaryotes (such as similar transcription machinery) and others with bacteria, making them a unique lineage with significant implications for understanding the evolution of life.
Virus
A virus is an obligate intracellular parasite consisting of genetic material (DNA or RNA) enclosed in a protein coat called a capsid, and sometimes surrounded by a lipid envelope. Viruses cannot reproduce independently; they hijack the cellular machinery of a host cell to replicate. They cause a wide range of diseases in humans, animals, and plants, and are also essential tools in molecular biology and gene therapy research.
Biofilm
A biofilm is a structured community of microorganisms — predominantly bacteria — that are attached to a surface and enclosed within a self-produced extracellular matrix of polysaccharides, proteins, and nucleic acids. Bacteria within biofilms exhibit markedly different gene expression from their planktonic (free-floating) counterparts and can be up to 1000 times more resistant to antibiotics and immune responses. Biofilms are clinically significant as causes of chronic infections (e.g., on medical implants and catheters) and are also exploited beneficially in wastewater treatment and bioremediation.
From New Latin "bacteria", plural of "bacterium", derived from Greek "bakterion" (βακτήριον) meaning "small staff" or "rod", referring to the rod-like shape first observed by early microscopists. The term was introduced in the 19th century by German naturalist Christian Gottfried Ehrenberg.