Bacteria are tiny single-celled organisms. They inhabit nearly every environment, from soil and water to the human body, and have diverse roles, some beneficial and others harmful.
Explanation
Bacteria are prokaryotes, meaning their genetic material is not enclosed in a nucleus. Each bacterium contains a single cell with a cell wall and cell membrane that encase its DNA and cytoplasm. Scientists classify bacteria by shape. Spherical forms are known as cocci. Rod-shaped forms are called bacilli, and spiral forms are spirochetes. Another way to classify bacteria is by the Gram stain. Gram-positive bacteria have a thick peptidoglycan layer in their cell walls and appear blue or purple under the stain. Gram-negative bacteria have a thinner peptidoglycan layer and a second membrane, and they appear red or pink under the stain. Bacteria differ in their need for oxygen. Some species require oxygen to live and are called aerobes. Others cannot survive when oxygen is present and are anaerobes. Facultative species can live with or without oxygen. Bacteria reproduce asexually through binary fission, which allows them to multiply quickly under favorable conditions. Many species are part of the normal flora on or inside the human body. These resident bacteria aid digestion, prevent colonization by pathogens and contribute to immune development. Some species cause disease by producing toxins or invading tissues. Infections range from mild conditions like sore throat to serious illnesses like sepsis.
Key Facts and Examples
Streptococcus species cause sore throats and skin infections. Staphylococcus species can cause boils or systemic infections. Escherichia coli lives in the intestines; some strains aid digestion, while others can cause foodborne illness. Lactobacillus species used in yogurt help ferment milk. Nitrogen-fixing bacteria such as Rhizobium enrich soil by converting atmospheric nitrogen into forms plants can use.
Bacteria are remarkably diverse microorganisms that influence ecosystems, industry and health. Recognizing their shapes, stains and oxygen requirements helps in identifying species and understanding how they affect our lives.
Related Terms: Prokaryote, Gram-positive bacteria, Gram-negative bacteria, Microbiome, Antibiotics