Domain Bacteria

• peptidoglycan; ester-linked; circular;

Distinctive Features of Bacteria

• Bacteria have ________________ walls, _______________ membranes, ___________ chromosomes, plasmids, and unique rRNA sequences.

• These traits define the domain and explain its adaptability.

Peptidoglycan Walls

Distinctive Features of Bacteria

Give bacteria a rigid, protective cell wall that helps them survive physical and chemical stress.

Peptidoglycan Walls

Distinctive Features of Bacteria

Prevents osmotic lysis — bacteria can live in hypotonic environments without bursting.

Peptidoglycan Walls

Distinctive Features of Bacteria

Provides shape stability — rod, cocci, spirilla shapes optimize nutrient uptake and motility.

Peptidoglycan Walls

Distinctive Features of Bacteria

Supports survival in extreme conditions — desiccation, pH changes, and mechanical stress.

Ester-linked Membranes

Distinctive Features of Bacteria

Membrane fluidity enables fast nutrient transport and efficient metabolic reactions.

Ester-linked Membranes

Distinctive Features of Bacteria

Membrane remodeling enables bacteria to adjust their lipid composition in response to temperature, toxins, or nutrient changes.

Ester-linked Membranes

Distinctive Features of Bacteria

Flexible electron transport chains allow bacteria to switch between aerobic, anaerobic, and facultative modes.

1. Fast replication

2. Fewer replication errors

3. Efficient gene expression

Distinctive Features of Bacteria

A circular chromosome gives bacteria several adaptive advantages:

1. ________________ because a circular chromosome replicates bidirectionally from one origin.

2. ____________________ because the chromosome has no telomeres or fragile ends.

3. ___________________ because a streamlined genome reduces energy cost and speeds transcription and translation.

• Reproduce quickly

• Exchange genes horizontally

• Metabolic flexibility

Why are bacteria successful?

Cocci; Bacilli; Spirals

Morphological Diversity

Shapes matter. __________ resist desiccation. ____________ grow faster. ___________ move efficiently through viscous environments like mucus.

Morphology often reflects ecological strategy.

Cocci - are round or nearly round cells

Morphological Diversity

Often have reduced surface area-to-volume ratios, making them more resistant to desiccation

Diplococci

Morphological Diversity

Pairs of cocci formed when cells divide once and remain attached (e.g., Neisseria)

Streptococci

Morphological Diversity

Chains of cocci produced by repeated division in one plane

Staphylococci

Morphological Diversity

Irregular grape-like clusters formed by division in multiple planes

Tetrads

Morphological Diversity

Groups of four cells arranged in a square, produced by division in two perpendicular planes

Sarcina

Morphological Diversity

Cube-like packets of eight cells formed by division in three perpendicular planes

Bacilli - are elongated, cylindrical cells.

Morphological Diversity

Rod shapes allow greater internal volume and often support faster growth.

Bacillus

Cocobacillus

Streptobacilli

Morphological Diversity

______________ - A single rod-shaped cell

______________ - A short, oval rod that resembles a coccus (e.g., Haemophilus influenzae)

______________ - Chains of rods formed by division in one plane

Palisades

Morphological Diversity

Cells arranged side-by-side like picket fences, often seen in Corynebacterium species

Spiral

Morphological Diversity

___________ bacteria have curved or helical shapes that often enhance motility

Spiral

Morphological Diversity

Their shape allows them to “drill” through tissues, move efficiently in mucus, and evade immune responses

Vibrio

Morphological Diversity

Comma-shaped, gently curved rods

Spirillum

Morphological Diversity

Rigid, spiral-shaped cells with external flagella

Spirochete

Morphological Diversity

Thin, flexible spirals with internal axial filaments (e.g., Treponema, Borrelia, Leptospira)

Gram-positive

Gram-negative

______________ bacteria - thick peptidoglycan layers.

______________ bacteria - thin peptidoglycan plus an outer membrane with LPS.

Gram-negative

______________ bacteria - The outer membrane of this type of bacteria makes them more resistant to many antibiotics

Photoautotroph

Mode - ____________________

Energy Source - Sunlight

Carbon Source - CO₂

Example - Cyanobacteria

Chemoautotroph

Mode - ____________________

Energy Source - Inorganic chemicals

Carbon Source - CO₂

Example - nitrifying bacteria, sulfur oxidizers, hydrogen oxidizers

Photoheterotroph

Mode - ____________________

Energy Source - Sunlight

Carbon Source - Organic compounds

Example - Purple non-sulfur bacteria

Chemoheterotroph

Mode - ____________________

Energy Source - Organic chemicals

Carbon Source - Organic compounds

Example - Proteobacteria, Firmicutes, Actinobacteria

Cyanobacteria

Phylogenetic Diversity

These are oxygenic phototrophs responsible for the Great Oxygenation Event.

Cyanobacteria

Phylogenetic Diversity

They use chlorophyll a and form heterocysts for nitrogen fixation.

Cyanobacteria

Phylogenetic Diversity

They remain major primary producers today

Proteobacteria

Phylogenetic Diversity

This is the most metabolically diverse phylum.

Proteobacteria

Phylogenetic Diversity

It includes nitrifiers, sulfur oxidizers, methane oxidizers, symbionts, and many pathogens.

The six classes reflect deep evolutionary splits.

Alpha

Phylogenetic Diversity

__________-proteobacteria - often associated with plants or intracellular lifestyles.

Rhizobium (nitrogen-fixing symbionts), Rickettsia (obligate intracellular parasites)

Beta

Phylogenetic Diversity

___________-proteobacteria - metabolically versatile soil and aquatic bacteria.

Neisseria (pathogens), Nitrosomonas (ammonia-oxidizing nitrifiers)

Gamma

Phylogenetic Diversity

__________-proteobacteria - the most diverse class; includes many medically important species.

Escherichia coli, Salmonella, Vibrio cholerae, Pseudomonas

Delta

Phylogenetic Diversity

________-proteobacteria - includes predators and sulfate-reducing bacteria.

Bdellovibrio (bacterial predator), Desulfovibrio (sulfur reducers).

Epsilon

Phylogenetic Diversity

__________-proteobacteria - microaerophiles adapted to animal digestive tracts. Helicobacter pylori, Campylobacter

Firmicutes

Phylogenetic Diversity

______________ are Gram positive, low GC bacteria. Many form endospores.

Firmicutes

Phylogenetic Diversity

They dominate gut microbiomes and include medically important genera.

Firmicutes

Phylogenetic Diversity

Examples:

Bacillus (aerobic endospore formers)
Clostridium (anaerobic endospore formers)
Lactobacillus (fermentative, important in food microbiology)
Streptococcus and Staphylococcus (major human pathogens)

Actinobacteria

Phylogenetic Diversity

These high GC, filamentous bacteria resemble fungi.

Actinobacteria

Phylogenetic Diversity

They decompose complex materials and produce most of our antibiotics

Actinobacteria

Phylogenetic Diversity

Examples:

Streptomyces (antibiotic producers; earthy soil smell from geosmin)

Mycobacterium (acid-fast pathogens such as M. tuberculosis)

Corynebacterium (diverse soil and host-associated species)

Spirochaetota

Phylogenetic Diversity

Spiral, flexible bacteria with axial filaments.

Spirochaetota

Phylogenetic Diversity

Their corkscrew motion allows them to move through viscous environments.

Several are major pathogens

Spirochaetota

Phylogenetic Diversity

Examples:

• Leptospira (leptospirosis)

• Borrelia (Lyme disease)

• Treponema (syphilis)