Eukaryotes and Viruses

Chapters 12 and 13

Fungi

Heterotrophic, Mainly Opportunistic Pathogens

Distinguishing Characteristics of Fungi

• Chemoheterotrophic• Cells walls composed of Chitin• Diverse Metabolic Capabilities for

Complex Carbohydrates• Xerophilic• Aerobic/Facultative Anaerobes• Prefer Low pH

Vegetative Growth• Filamentous Fungi

• Yeasts

• Dimorphic Fungi

Filamentous Fungi• Hyphae

(individual strands)– Septate– Coenocytic

• Mycelium (mass of hyphae)

• Aerial Hyphae• Mass of Conidia

Yeast• Bud• Bud Scar

• Pseudohyphae

Dimorphic Fungi• Medically very

important• Hyphae in the

Environment, Yeast in the host

• Temperature and CO2 are common triggers

Fungal Lifecycle• Haplodiplontic Lifecycles

• Asexual Cycle

• Sexual Cycle

Haplodiplontic Life CycleGametophyte

(n)

Sporophyte(2n)

Egg

Sperm

Zygote

Embryo

Sporangia

Sporocyte

Spores

Haploid

Diploid

Asexual Spores• Genetically Identical

to the parent• Genetically Haploid• Several Types– Conidia– Blastoconidia– Arthroconidia– Chlamydoconidia– Sporangiospores

Sexual Spores• Haploid Spores

Arising from a Diploid Cell

• Genetic Recombination of compatible mating types

• Fungi are classified on the basis of their sexual cycles.

Medically Important Phyla• Zygomycota

• Ascomycota

• Basidiomycota

• Deuteromycota (Asexual Fungi)

Zygomycota• Coenocytic Hyphae• Not a

phylogentically distinct group.

• Sporoangiospores and Zygospores

• Rhizopus is a common genus.

Ascomycota• Septate Hyphae and

Yeasts• Largest group of

classified fungi• Most Deuteromycota

are classified in this group by Genetics

• Ascospores (in an ascus) and Conidia

Basidiomycota• Septate Hyphae• Basidiospores

produced on Basidium, some produce conidia (though this is crude terminology)

Deuteromycota• Depreciated, though still used Taxon• Holding Phyla with no observed

sexual state• Most have been reclassified as

Ascomycota based on Genetics• Leads to confusion over

nomenclature– Telomorph : Sexual State (preferred

name)– Anamorph : Asexual State (common

name)

Fungal Disease• Mycoses are not common but difficult

to treat.• Mycoses are defined by the depth of

tissue affected.• Most fungi are either superficial or

opportunistic pathogens… though overt pathogens exist.

Examples of Fungal Disease

Protozoa

Diverse Unicellular Eukarya Pathogens

Protozoans• Phylogenetically, a diverse and ill-

defined group.• Medically we are worried about the

heterotrophs, not the photosynthetic phyla

• Complex lifecycles with unique stages– Trophozoite– Schizogony– Cyst

Protists Are NOT Monophyletic

Archaezoa• Lack

Mitochondria, but possess relics called mitosomes.

• Move by means of Flagella

• Possess two nuclei.

Giardia intestinalis

Microspora• No mitochondria • No microtubules• Obligate intra-

cellular pathogens

• Common in AIDS

Amoebozoa• Phylogenetically

these organisms are not linked to a definite clade.

• Movement through pseudopods

Apicomplexa• Named for the

Apical complex, an organelle used for cell penetration.

• Complex Lifecycles with both a definitive and intermediate host

Plasmodium species

Eugelnozoa• Hemoflagellates, more appropriately

called Kinetoplastids, are the pathogenic members.

• Possess unique single mitochondrion called kinetoplasts.

• Many are Parasitic

Helminths

The Worms

Characteristics of Pathogens• They may lack a digestive system• They have a reduced nervous system• Lacking or atrophied movement

systems• Complex reproductive systems• May be dioecious or monoecious

Platyhelminthes• Flatworms, so called for overall flat

body plan.• Actually the Subphylum Neodermata• All have a Neodermis (also called a

cuticle) to protect them from the host and lack adaptations such as eyepores (found in free-living flatworms)

Trematodes• Flukes• Ventral and Oral

Sucker to attach to host tissue.

• Life Cycles involve more than a single host and mutiple developmental stages

Schistosoma Life Cycle

Cestodes• Tapeworms• Three body

sections, scolex, neck and proglottids

• No digestive system

• Mature proglottids are released through feces of host.

Phylum Nematoda• Roundworms, due to the circular

body cross-section.• Not to be confused with Phylum

Annileda, the segmented worms (i.e. Earthworms)

• Complete digestive systems• Sexually dimorphic• Numerous through out the

environment

Comparative Anatomy

Nematoda Diseases