Lecture 12: Early Earth History, Bacterial Diversity, and Taxonomy

Vocabulary practice cards covering early Earth evolutionary history, taxonomy, and major bacterial phyla (Proteobacteria, Cyanobacteria, Actinobacteria, and Firmicutes).

Hadean Era

The geological era directly following the formation of Earth, characterized by extreme temperatures, UV radiation, and hostile conditions.

Primordial Soup

The blend of gases on early Earth that produced a broth of organic molecules, which eventually formed the building blocks of life.

Archean Era

The era of Earth from around $4\text{ to }2.5\text{ billion years ago}$ during which the first cells evolved.

Great Oxygenation Event

An event occurring around $2.5\text{ billion years ago}$ where the environment produced enough oxygen to accumulate in the atmosphere, causing mass extinction of anaerobic life and enabling the evolution of eukaryotes.

Proterozoic Era

The era of Earth marked by massive atmospheric changes, the emergence of eukaryotes around $1.7\text{ billion years ago}$, and the Cambrian Explosion around $0.6\text{ billion years ago}$.

Phylogeny

The evolutionary history and relationships between organisms, determining how closely related organisms are based on similarities in DNA.

Taxonomy

The classification and organization of organisms based on phylogeny, arranged into hierarchical groups from domain down to species.

Binomial Nomenclature

The standard system of naming organisms in scientific writing where only the genus and species names are italicized.

Proteobacteria

A diverse and environmentally important bacterial phylum consisting of mostly Gram-negative bacteria divided into $6$ classes.

Alphaproteobacteria

A class of Proteobacteria united by their ability to live as oligotrophs, with some members existing as obligate intracellular pathogens.

Oligotroph

An organism capable of living in low-nutrient environments.

Copiotroph

An organism capable of living in high-nutrient environments.

Pelagibacter ubique

One of the most common bacteria on Earth; an extremely small Alphaproteobacteria found in the ocean that requires very few nutrients.

Obligate Intracellular Pathogens

Pathogens that must reside within host cells to survive and replicate, such as species in the genus Rickettsia.

Rickettsia

A genus of obligate intracellular Alphaproteobacteria that causes Rocky Mountain spotted fever (R. rickettsii) and epidemic typhus (R. prowazekii).

Betaproteobacteria

A diverse and large class of Proteobacteria with no unifying characteristics, frequently copiotrophic and commonly growing between oxic and anoxic environments.

Bacteroides thetaiotamicron

A Gram-negative, anaerobic bacterium residing in the human gut that breaks down fibers and stimulates the host immune system.

Bordetella pertussis

A pathogenic Betaproteobacteria that causes whooping cough by attaching to cilia in the lungs and producing toxins; preventable by the TDAP vaccine.

Gammaproteobacteria

The most diverse group and class within the phylum Proteobacteria.

Aliivibrio fischeri

A Gram-negative, curved rod bacterium that produces bioluminescence via the lux operon and forms symbiotic, camouflaging relationships with marine animals.

Vibrio vulnificus

A pathogenic, Gram-negative, curved rod bacterium found in marine coastal environments that can cause necrotizing wound infections.

Cyanobacteria

A phylum of oxygenic photoautotrophs that can fix $CO_2$ and inhabit diverse environments as unicellular, colonial, or filamentous forms.

Diazotrophs

Nitrogen-fixing bacteria capable of converting triple-bonded atmospheric $N_2$ into ammonium.

Heterocysts

Specialized non-oxygen-producing cells in certain diazotrophs dedicated to carrying out $N_2$-fixation.

Gas Vesicle

A specialized protein structure enclosing an air bubble that allows cyanobacteria to regulate position in the water column at lower light intensities for optimal photosynthesis.

Actinobacteria

A phylum of Gram-positive, short rod bacteria characterized by high G/C content.

Streptomyces

A genus of Actinobacteria containing over $500$ species responsible for the earthy odor of soils in alkaline to neutral pH, approximately half of which produce antibiotics.

Firmicutes

A phylum of Gram-positive, rod-shaped, endospore-forming bacteria characterized by low G/C content, including the genera Bacillus and Clostridium.

Bacillus anthracis

A Gram-positive, encapsulated, endospore-forming rod bacterium discovered by Robert Koch ($1876$) that causes anthrax in cutaneous, inhalation, gastrointestinal, or injection forms.

Clostridium tetani

A Gram-positive, motile, endospore-forming obligate anaerobe found in soil, feces, and rusty metals that causes tetanus via deep puncture wounds.

Clostridium botulinum

A Gram-positive, motile, endospore-forming anaerobic rod that causes flaccid paralysis (botulism) typically $12\text{--}36\text{ hours}$ after ingesting improperly canned foods.