The Evolution of Microbial Life
Human Microbiota
Microorganisms reside on the body, mainly on the skin, mouth, nasal passages, digestive, and urogenital tracts.
They weigh between 2 and 5 pounds.
Antibiotic Resistance
Antibiotics kill infectious microorganisms; penicillin was the first widely used one in the 1940s.
Bacteria can resist antibiotics through mutations and the transfer of resistant genes via transposons and plasmids.
MRSA (methicillin-resistant Staphylococcus aureus) is a dangerous superbug that causes systemic infections.
Overuse of antibiotics in humans and livestock contributes to antibiotic resistance.
History of Life
Earth formed about 4.6 billion years ago.
Prokaryotes evolved around 3.5 billion years ago, began oxygen production about 2.7 billion years ago, and lived alone for 1.7 billion years.
Eukaryotes evolved 1.8 billion years ago, and multicellular eukaryotes evolved 1.2 billion years ago.
The Cambrian explosion occurred about 541 million years ago.
Plants, fungi, and insects started colonizing land about 500 million years ago.
Modern humans, Homo sapiens, originated roughly 195,000 years ago.
Origin of Life
The first organisms may have originated through chemical evolution in four stages:
Synthesis of small organic molecules.
Joining small molecules into macromolecules.
Packaging molecules into pre-cells.
Origin of self-replicating molecules enabling inheritance.
Stanley Miller's experiment simulated early Earth conditions and produced organic molecules.
RNA may have been the first self-replicating molecule, later replaced by DNA.
Prokaryotes
Prokaryotes lack a nucleus and membrane-bound organelles.
They have cell walls and can have capsules, flagella, and fimbriae.
The three common shapes are cocci (spherical), bacilli (rod-shaped), and spiral.
They reproduce via binary fission and can form endospores to survive harsh conditions.
Some harvest energy from inorganic substances.
Prokaryotic vs. Eukaryotic Cells
Prokaryotic cells:
Evolved ~3.5 billion years ago.
Found in bacteria and archaea.
Smaller and simpler.
No membrane-bound organelles.
Nucleoid region with a single, circular chromosome.
Eukaryotic cells:
Evolved ~2.1 billion years ago.
Found in protists, plants, fungi, and animals.
Larger and more complex.
Membrane-bound organelles (e.g., nucleus, ER).
Nucleus containing one or more linear chromosomes.
Prokaryotic Nutrition & Impact
Symbiosis is a close association between different species.
Some cyanobacteria perform nitrogen fixation, converting atmospheric nitrogen into usable forms for plants.
Prokaryotes recycle chemical elements and break down organic waste.
Bioremediation uses organisms to remove pollutants.
Bacteria and Archaea
Bacteria and Archaea are the two main branches of prokaryotic evolution.
Archaea include extreme thermophiles (heat lovers), extreme halophiles (salt lovers), and methanogens (methane producers).
Bacteria and Disease
Pathogenic bacteria cause disease by producing exotoxins or endotoxins.
Sanitation, antibiotics, and education are key to preventing bacterial diseases.
Some bacteria, like anthrax and Clostridium botulinum, can be used as bioweapons.
Intestinal Microbiota and Obesity
Experiment: Transplanted microbiota from obese and lean twins into germ-free mice.
Results: Mice receiving microbiota from obese donors became more obese, while those from lean donors remained lean.
Protists
Eukaryotes that are not fungi, animals, or plants.
Can be photosynthetic (algae), heterotrophic, parasitic, or mixotrophic.
Live in diverse habitats, mainly aquatic.
Protozoans
Protists that live primarily by ingesting food.
Include flagellates, amoebas, apicomplexans, and ciliates.
Algae
Photosynthetic protists and cyanobacteria supporting food chains.
Include dinoflagellates, diatoms, and green algae.
Seaweeds
Large, multicellular marine algae classified into green, red, and brown algae.
Streptococcus mutans
A biofilm-forming bacteria that metabolizes sugars, produces lactic acid, and attacks tooth enamel.