Microorganisms: Bacteria Overview

Characteristics of Bacteria

• Bacteria are prokaryotic microorganisms and mostly single-celled, typically a few micrometers in length.
• Ubiquitous organisms inhabiting diverse environments like soil, water, hot springs, radioactively impacted areas, and deep geological formations.
• Play essential roles in nutrient cycling, including nitrogen fixation and decomposition of organic matter.

Ecological Importance

• Extremophiles around hydrothermal vents and cold seeps convert compounds like hydrogen sulfide and methane into energy, supporting local ecosystems.
• Participate in various symbiotic relationships: mutualistic, commensal, and parasitic with plants and animals.
• Vital for processes like sewage treatment, oil spill remediation, fermentation in cheese and yogurt production, and biomining.

Human Interaction and Health Implications

• The human microbiome contains about 10^13 to 10^14 bacteria, primarily beneficial or innocuous; significant populations reside in the gut and on the skin.
• Pathogenic bacteria can cause serious infectious diseases, including cholera, tuberculosis, and anthrax.
• Antibiotics are critical in treating bacterial infections but contribute to rising antibiotic resistance; they're also used in agriculture.

Classification and Evolution

• Once categorized as plants (class Schizomycetes), bacteria are recognized as prokaryotes, distinct from eukaryotic cells which contain nuclei and organelles.
• In the 1990s, it was established that prokaryotes include two major domains: Bacteria and Archaea, diverging from a common ancestral origin.
• Early bacterial forms emerged approximately 4 billion years ago; they dominated life forms for about 3 billion years.

Ancestry and Evolutionary Significance

• Bacterial phylogeny can be reconstructed through gene sequences, revealing they diverged before Archaea and Eukarya.
• The most recent common ancestor of bacteria and archaea is thought to have been a hyperthermophile existing between 2.5 billion to 3.2 billion years ago.
• Endosymbiotic events led to the evolution of eukaryotic cells, with ancient bacteria forming mitochondria and chloroplasts through primary endosymbiosis.

Etymology

• The term "bacteria" is derived from the Neo-Latin "bacterium," which comes from the Ancient Greek word "βακτήριον" (baktḗrion), meaning "staff" or "cane," referencing the initial rod-shaped observations of these organisms.