5_Microbial Symbioses Slides

Symbiosis

A close and long-term biological interaction between two organisms of different species

Mutualism

Both living things help each other and benefit from the relationship

Coevolution

Two or more species shape each other's evolution through close ecological contact

Lichen

Mutualistic association of a fungus and an alga or cyanobacterium

Consortia

A community of 2 or more microbial organisms living
together and cooperating that is mutualistic and found in freshwater environments

Consortia example

Epibionts-green sulfur bacteria

Epibionts-green sulfur bacteria

Surround and attach to a central flagellated, colorless rod-shaped bacterium

Examples of Plants as microbial habitats

• Root nodules
• Mycorrhizae
• Crown gall disease

Root nodules

Leguminous plants and nitrogen fixing bacteria

Rhizobium

• Mutualistic relationship, legumes obtain fixed nitrogen, bacteria receive carbon compounds and protected niche

• a cornerstone process in sustainable agriculture and the global nitrogen cycle

Crown gall disease

• Agrobacterium parasite infect the plants causing tumor-like swelling (galls) near roots, branches and stems.

• The galls become so large the plant cannot properly uptake water and nutrients from the soil.

Ti plasmid

used in the genetic engineering of plants

Mycorrhizae

Mutualistic relationship, plant provides sugars, and fungus has long thread like protrusions in the soil to bring water and nutrients to the plant.

Ectomycorrhiza

• symbiotic partnership between fungi and the roots of woody plants where the fungus forms a protective sheath around the outside of the roots rather than entering the plant cells

• Conifers, beech, oak trees

Endomycorrhiza

• beneficial fungi that penetrate the cell walls of plant roots to form a shared, cooperative network

• Arbuscular mycorrhizae (AM), 70-90% all terrestrial plants

Human microbiome

• Eat food
• 1-4 hours
• Large intestine
• Increase in bacterial numbers

Heritable Symbionts of Insects

• Secondary symbionts. Not required for reproduction, Not always present in every individual, Can invade different cells and live extracellularly, Must provide a benefit (nutritional, protection from environment, protection from pathogens)
• Some parasitic symbionts manipulate host's reproductive tissue

Termites

decompose cellulose and hemicellulose with assistance from symbiotic bacteria

Hawaiian Bobtail Squid

• A mutualistic symbiosis between the marine bacterium Aliivibrio fischeri and the _________

• The _________ harbors large populations of the bioluminescent A.
  fischeri in a specialized structure (light organ)

• Light emitted from bacteria camouflages the ________ from predators

Mucous Membranes

Colonization's frequently begin at sites in the animal's _____________

Microflora of the Skin

• Based on microenvironments

• Environmental and host factors can also influence
  skin microflora

Microflora of the Oral Cavity

• Complex microbial community
– Most microorganisms are facultatively aerobic
– Some are obligately anaerobic (Bacteroides)
– Some are obligately aerobic (Neisseria, Acinetobacter)
• Most abundant - Streptococci, Veillonella parvula

Microflora of the Gastrointestinal Tract

Microflora of Mucosal Tissues: Respiratory

Upper Respiratory Tract Flora - Staphlyococci, Streptococci, diphtheroid bacilli, and gram negative cocci

Microflora of Mucosal Tissues: Urogenital Tract

• Kidneys and bladder (low level to no bacteria
present)
• Urethra - Facultative aerobic, gram negative

Lactobacillus acidophilus

helps maintain an acidic environment in vagina

The presence of microbes can lead to

• Infection
• Disease

Microbial Pathogenesis

Factors Affecting Adherence/Attachment

• Capsule/ slime layer

• Adherence proteins

• Lipoteichoic acid

• Fimbriae (pill)

LD50

The amount of agent that kills 50% of the animals in a test group

Toxicity

Organism causes disease by means of a toxin that inhibits host cell function or kills host cells

Exotoxins

Proteins released from the pathogen cell as it grows

Exotoxin categories

Cytotoxins (hemolysins), AB toxins (botulism, tetanus, cholera), Superantigen toxins

Cytotoxins (cytolytic toxins)

Cause cell lysis and death

Hemolysins

Toxins that lyse red blood cells

A Subunit of AB Toxin

The enzyme component that enters the host cell cytoplasm and causes direct cellular damage or death by altering key metabolic or protein synthesis processes

B Subunit of AB Toxin

The portion that recognizes and attaches to specific receptor molecules on the surface of the host cell, controlling which cell types the toxin targets and helping the A subunit get inside.

AB Toxin Process Illustration

AB Toxin Binding

The B subunit binds to a specific receptor on the target host cell membrane.

AB Toxin Entry

The cell takes in the toxin through endocytosis.

AB Toxin Separation

Inside the cell, changes in acid levels or chemical cleavage cause the A and B subunits to separate.

AB Toxin Action

The active A subunit moves into the cytoplasm to disable vital cell machinery, such as blocking protein synthesis or stopping nerve signals.

Botulinum Toxin (Clostridium botulinum)

Causes flaccid paralysis

Tetanus Toxin (Clostridium tetani)

Causes spastic paralysis

Cholera Toxin

Rice Water Stool

Superantigen toxins

powerful microbial proteins that cause extreme, non-specific immune system activation

Endotoxins

• The lipopolysaccharide portion of the cell envelope of certain gram-negative Bacteria, which is a toxin when solubilized

• Release of LPS (Lipid A) when Gram negative bacteria die

• Lipid A causes inflammation, fever, shock

Innate Resistance to Infection

Risk Factors for Infection

Compromised host: Age, Stress, Diet, Certain genetic conditions