ch12 - eukaryotic members of the microbial world

the microbial world

all living things classified in one of three groups (domains)

• three domains: bacteria, archaea, eucarya

domain eucarya

all members are

• eukaryotic

  • contain membrane-bound organelles

    • nucleus (houses dna), mitochondria, endoplasmic reticulum, etc.

• more complex

• single cell or multicellular

• asexual or sexual reproduction

includes

• fungi

• algae

• protozoa

• helminths

fungi

diverse

• single-celled = yeast

• multicellular = molds, mushrooms

cell wall consists of chitin

major decomposers

• excrete enzymes to degrade larger molecules

• break down organic matter into smaller nutrients that can be absorbed and used by other organisms as a food source

exist in many places

• mostly terrestrial

some are pathogenic

yeasts

single celled fungi

spherical, oval or cylindrical

reproduction through binary fission or budding

• budding: a small bud forms on the parent cell, grows larger, and eventually detaches to become a new yeast cell

fungi - molds and dimorphic fungi

molds

• produce single-celled reproductive spore → germinates and develops into hyphae

• filamentous fungi contain hyphae → a collection of hyphae is called a mycelium

  • moldy and fuzzy place

dimorphic fungi

• can have more than one shape, several different forms

• can grow as a yeast or mold depending on the environment

• many are pathogenic

many cause disease in plants

• only a few cause disease in humans

fungal diseases in humans

immunocompromised - more susceptible

• weakened immune system

fungi cause disease in 3 ways

• allergic reaction

  • result from inhaling fungal spores

  • may lead to inflammation and other forms of disease

• reaction to fungal toxin

  • many fungal toxins have hallucinogenic properties

    • Ergot: caused by Claviceps fungi; historically eating moldy grain or bread could cause ergot poisoning, which can include hallucinations

  • certain species produces aflatoxin implicated in cancer

    • Aspergillus flavus

• mycoses

  • fungi grow on or in the body → disease

    • some fungal infections can affect the lungs and cause pneumonia, especially in immunocompromised people.

  • candida albicans - yeast, part of normal flora

    • overgrowth can cause disease

    • overgrowth due to change in pH or antibiotic therapy

    • dermatitis (ulceration of skin)

      • blisters, ulceration, very severe diaper rash

    • yeast infections (vaginal, oral - thrush)

      • vaginal: overgrowth of Candida albicans

        • if the normal acidic vaginal pH, environment/microbiota with Lactobacillus bacteria producing lactic acid is disrupted, such as after antibiotic therapy, Candida can overgrow

        • can cause itching, irritation, and abnormal discharge

        • thrush: usually seen in immunocompromised people, Candida overgrowth

fungi - economic impact

negative economic impact of fungi

• destruction of human good supply causing starvation

  • spoilage of food and crops

  • Irish potato famine (1845-1847)

    • water mold decimated crop

    • an estimated 1.5 million people died

      • 25% of the population of Ireland

• toxins production

  • aflatoxins produced by Aspergillus flavus species; found in grains, peanuts; carcinogenic

    • can be difficult for the body to eliminate completely, and repeated exposure can cause harmful effects over time

  • rye mold Claviceps purpurea (ergot) produces hallucinogenic toxin → ergotism

positive economic importance of fungi

• commercially important

  • production of beer, wine, bread, cheese, antimicrobial agents

• genetic and biotechnology applications

  • yeast genetically engineered to produce human products (human insulin, hepatitis B vaccine)

algae

diverse group

• unicellular (microscopic)

• multicellular (macroscopic)

found in both fresh and salt water, and soil

have rigid cell wall of cellulose

contain chlorophyll → photosynthetic

• use sunlight to make organic compounds (such as sugars) from CO2 and water

• release oxygen as a byproduct

do not cause disease regularly

• toxins poisonous to humans → disease

• seasonal algal bloom (“red tide”)

  • dinoflagellates

    • eaten by shellfish and produce neurotoxins

      • affect neurons in the brain

    • humans eat shellfish and suffer paralytic shellfish poisoning (respiratory failure)

      • may die from this unless immediate help is received

protozoa

microscopic, single-celled

found in water, on land, as parasites

more complex, larger than prokaryote

do not have cell wall

have complex life cycle

most are motile via

• cilia, flagella, or pseudopodia (like in amoeba that put out pseudopods)

• cilia like the ones on the perimysium

protozoa - many cause disease

Giardia lamblia - giardiasis; spread via fecal contaminated water

• causes foaminating diarrhea → dehydration

• very persistent - can stay with person for a long time (30 years)

Trichomonas - STD

• seen mostly in females (vaginitis) - causes irritation

  • no long-term effects

• fewer outward symptoms in males

• identify by wet mounts

protozoa - plasmodium

causes malaria

• intracellular pathogen that infects red blood cells

• transmitted by mosquitoes

• number one cause of death of pregnant women in world (in US → domestic violence)

  • infect ~219 million/year; ~660,000 deaths

• identify by blood smear

protozoa - toxoplasma

causes toxoplasmosis

• associated with cats → litter box

• affects pregnant women → pass to fetus

  • this pathogen can cross the placenta and infect the fetus in the womb

• affects immunocompromised individuals (eating undercooked beef)

  • affects brain (causes hemolytic process → bleeding and dementia); identify by brain biopsy

multicellular parasites: helminths

multicellular, parasitic worms

• free-living and parasitic worms

• round worms (nematodes)

• flat worms (tapeworms/cestodes)

• trematodes (flukes)

obtain from water, soil

common in children all over the world in developing countries

multicellular parasites: helminths - nematodes

round worms

• invade GI tract and blood stream

• pinworms - ingested in food

  • anal itching (deposition of eggs in perianal skin)

• ascaris - ingested in fish

  • lives in GI tract, robs host of nutrients

    • causes children not to thrive

    • blockage of GI tract

  • can enter bloodstream → can cause infection in the lungs

• Trichinella - ingested in animal flesh

  • disease is trichinosis by eating wild pork, pig etc.

• reproduced in GI tract

• female will birth a lot of larvae which will travel to and encyst in muscles

  • have to kill the larvae so humans don’t get infected

multicellular parasites: helminths - cestodes, trematodes

helminths - parasitic worms

• cestodes - flatworms

  • tapeworms (beef and pork)

  • remain in GI tract and rob host of nutrients or migrate to muscles and encysts

  • hooklets attach to intestinal wall

• trematodes - flukes

  • found in lakes and ponds

  • transmitted through undercooked crayfish

  • sucks fluid from host

multicellular parasites: arthropods

serve as vectors of transmission

• include

  • insects

    • mosquitoes - transmission of malaria, dengue fever, WNV

    • fleas - transmit plague (Yersinia pestis)

  • ticks

    • transmission of Rocky Mountain Spotted fever and Lyme disease

  • lice

    • body lice - transmission of typhus and other fevers

  • arachnids - mites

    • trigger asthma

    • causes intense itching