Lecture 5: Survey of the microbial worldEdith Porter, M.D.

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Classification of microorganisms▪ Taxonomy▪ Three domain system: Bacteria, Archaea,

Eukarya Prokaryotes▪ Bacteria▪ Archaea

Eukaryotes▪ Protozoa▪ Algae▪ Fungi▪ Helminths

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The science of classifying organisms Provides universal names for

organisms Provides a reference for identifying

organisms Initially based on morphology and

biochemical assays Now based on nucleic acid sequencing

(16S and 18S rRNA analysis)

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The study of the evolutionary history of organisms

All Species Inventory (2001–2025) To identify all species of life on Earth

Species definition Eukaryotes: breed among themselves Prokaryotes: > 97% homology in 16S rRNA

Cladograms used to establish relation ship

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Taxonomy is the science of classification using a hierarchical system

Universal ancestor The three domains differ in presence of

a nucleus (eukarya), ether linked lipids (archaea) and use of formylmethionine as started amino acid in protein synthesis (bacteria)

Cladograms are used to establish evolutionary relationships

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Obligate intracellular bacteriaCannot proliferate outside of a host

cellSelected human pathogens

Rickettsia Chlamydia

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Transmitted by ticks or lice Infects vascular endothelial cellsR. rickettsii: Rocky Mountain spotted

fever

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Eukaryotic Aerobic or facultatively anaerobic Chemoheterotrophic Most are decomposers Asexual and sexual spore formation

For Reproduction, not endurance!! Broad use of fungi

Food, food production, drugs Mycology is the study of fungi

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, absorptive

YEASTS Unicellular Proliferate by budding

or fission Candida albicans

MOLDS Multicellular Septated and unseptated

hyphae Mass of hyphae is

mycelium Aspergillus spec.,

Rhizopus spec.

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Switch growth phase depending on environmental conditions

Pathogenic dimorphic fungi are yeastlike at 37°C and moldlike at 25°C

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Systemic mycoses: Deep within bodySubcutaneous mycoses: Beneath the skinCutaneous mycoses: Affect hair, skin, and

nailsSuperficial mycoses: Localized, e.g., hair

shaftsOpportunistic mycoses: Caused by

normal microbiota or environmental fungi Note: antibiotics do not work against fungi!

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Yeasts Candida: Candidiasis Cryptococcus: Meningitis

Molds Aspergillus: Lung infection in neutropenic patients Rhizopus, Mucor: in diabetes patients

Dimorphic Coccidioides: Lung infections Histoplasma: Lung infections

Dermatophytes Trichophyton, Epidermophyton: Tinea

Eukaryotic Always unicellular Chemoheterotrophs Digestion in vacuoles Often complex life cycles with multiple

hosts and vectors Some produce cysts

Resistant survival forms Vegetative form is a trophozoite Reproduction

Asexual Sexual reproduction 25

Archaezoa: Trichomonas, Giardia Amaebazoa: Entamoeba Apicomplexa: Plasmodium Ciliophora: Balantidum Euglenozoa: Trypanosoma

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Eukaryotic Multicellular, organ differentiation Kingdom: Animalia

Phylum: Platyhelminthes (flatworms)▪ Class: Trematodes (flukes)▪ Class: Cestodes (tapeworms)

Phylum: Nematodes (roundworms) Chemoheterotrophic Multiple hosts

Intermediate host Definitive host: adult form develops, sexual

reproduction29

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Monoecious (hermaphroditic) Male and female reproductive systems in

one animalDioecious

Separate male and femaleEgg larva(e) adult

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Oral sucker: food uptake Incomplete digestive tract

Ventral Sucker: Attachment Mostly hermaphroditic (monoecious)

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Sucker for attachment

No digestive tract Food uptake by

absorptionHermaphrodites

(monoecious)Scolex, neck,

proglottides

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Dioecious (male, female) Complete digestive tract Caenorrhabditis elegans: model system

Necator americanus (hook worm)

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Fungi Molds (septated, unseptated), yeast,

dimorphic Sexual and asexual spores Mycoses: local or systemic impairment

of host defenseProtozoa: always unicellular, often

vectorsHelminths: always multicellular,

complex life cycles

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Eukaryotic Multicellular, organ differentiation Kingdom: Animalia

Phylum: Platyhelminthes (flatworms)▪ Class: Trematodes (flukes)▪ Class: Cestodes (tapeworms)

Phylum: Nematodes (roundworms) Chemoheterotrophic Multiple hosts

Intermediate host Definitive host: adult form develops, sexual reproduction