chapter05 lecture

Foundations in Microbiology

Sixth Edition

Chapter 5Eucaryotic Cells and

Microorganisms

Lecture PowerPoint to accompany

Talaro

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The History of Eucaryotes• They first appeared approximately 2 billion

years ago.• Evidence suggests evolution from procaryotic

organisms by symbiosis.• Organelles originated from procaryotic cells

trapped inside them.

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External Structures• Locomotor appendages

– flagella • long, sheathed cylinder containing microtubules in a 9+2

arrangement• covered by an extension of the cell membrane • 10X thicker than procaryotic flagella• function in motility

– cilia • similar in overall structure to flagella, but shorter and

more numerous• found only on a single group of protozoa and certain

animal cells• function in motility, feeding and filtering

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External Structures• Glycocalyx

– an outermost boundary that comes into direct contact with environment

– usually composed of polysaccharides– appears as a network of fibers, a slime layer or a

capsule– functions in adherence, protection, and signal

reception– beneath the glycocalyx

• Fungi and most algae have a thick, rigid cell wall.• Protozoa, a few algae, and all animal cells lack a

cell wall and have only a membrane.

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External Boundary Structures• Cell wall

– rigid, provides structural support and shape– Fungi have thick inner layer of polysaccharide

fibers composed of chitin or cellulose and a thin layer of mixed glycans.

– algae – varies in chemical composition; substances commonly found include cellulose, pectin, mannans, silicon dioxide, and calcium carbonate

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External Boundary Structures• Cytoplasmic (cell) membrane

– typical bilayer of phospholipids and proteins– sterols confer stability– serves as selectively permeable barrier in

transport– Eucaryotic cells also contain membrane-bound

organelles that account for 60-80% of their volume.

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Internal Structures• Nucleus

– compact sphere, most prominent organelle of eucaryotic cell

– nuclear envelope composed of two parallel membranes separated by a narrow space and is perforated with pores

– contains chromosomes– nucleolus – dark area for rRNA synthesis and

ribosome assembly

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Internal Structures• Endoplasmic reticulum – two types:

– Rough endoplasmic reticulum (RER)– originates from the outer membrane of the nuclear envelop and extends in a continuous network through cytoplasm; rough due to ribosomes; proteins synthesized and shunted into the ER for packaging and transport; first step in secretory pathway

– Smooth endoplasmic reticulum (SER)– closed tubular network without ribosomes; functions in nutrient processing, synthesis and storage of lipids, etc.

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Internal Structures• Golgi apparatus

– consists of a stack of flattened sacs called cisternae– closely associated with ER– Transitional vesicles from the ER containing

proteins go to the Golgi apparatus for modification and maturation.

– Condensing vesicles transport proteins to organelles or secretory proteins to the outside.

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Internal Structures• Lysosomes

– vesicles containing enzymes that originate from Golgi apparatus

– involved in intracellular digestion of food particles and in protection against invading microbes

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Internal Structures• Mitochondria

– consists of an outer membrane and an inner membrane with folds called cristae

– Cristae hold the enzymes and electron carriers of aerobic respiration.

– divide independently of cell– contain DNA and procaryotic ribosomes– function in energy production

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Internal Structures• Chloroplast

– found in algae and plant cells– outer membrane covers inner membrane folded

into sacs, thylakoids, stacked into grana– larger than mitochondria– contain photosynthetic pigments– convert the energy of sunlight into chemical

energy through photosynthesis– primary producers of organic nutrients for other

organisms

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Internal Structures• Ribosomes

– composed of rRNA and proteins– 40S and 60S subunits form 80S ribosomes– larger than procaryotic ribosomes– function in protein synthesis

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Internal Structures• Cytoskeleton

– flexible framework of proteins, microfilaments and microtubules form network throughout cytoplasm

– involved in movement of cytoplasm, amoeboid movement, transport, and structural support

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Survey of Eucaryotic Microbes

• Fungi• Algae• Protozoa• Parasitic worms

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Kingdom Fungi• 100,000 species divided into 2 groups:

– macroscopic fungi (mushrooms, puffballs, gill fungi)

– microscopic fungi (molds, yeasts)• Majority are unicellular or colonial; a few

have cellular specialization

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Microscopic Fungi• Exist in two morphologies:

– yeast – round ovoid shape, asexual reproduction– hyphae – long filamentous fungi or molds

• Some exist in either form – dimorphic – characteristic of some pathogenic molds

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Fungal Nutrition• All are heterotrophic• Majority are harmless saprobes living off dead

plants and animals• Some are parasites, living on the tissues of other

organisms, but none are obligate; mycoses – fungal infections

• Growth temperature 20o-40oC• Extremely widespread distribution in many

habitats

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Fungal Organization• Most grow in loose associations or colonies• Yeast – soft, uniform texture and appearance • Filamentous fungi – mass of hyphae called

mycelium; cottony, hairy, or velvety texture– hyphae may be divided by cross walls – septate– vegetative hyphae – digest and absorb nutrients– reproductive hyphae – produce spores for

reproduction

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Fungal Reproduction• Primarily through spores formed on reproductive

hyphae• Asexual reproduction – spores are formed

through budding or mitosis; conidia or sporangiospores

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Fungal Reproduction

• Sexual reproduction – spores are formed following fusion of male and female strains and formation of sexual structure

• Sexual spores and spore-forming structures are one basis for classification.

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Fungal ClassificationSubkingdom Amastigomycota – terrestrialinhabitants including those of medical importance:1. Zygomycota – zygospores; sporangiospores and some

conidia2. Ascomycota – ascospores; conidia3. Basidiomycota – basidiospores; conidia4. Deuteromycota – majority are yeasts and molds; no

sexual spores known; conidia

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Fungal Identification• Isolation on specific media• Macroscopic and microscopic observation

of:– asexual spore-forming structures and spores– hyphal type– colony texture and pigmentation– physiological characteristics– genetic makeup

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Roles of Fungi• Adverse impact

– mycoses, allergies, toxin production– destruction of crops and food storages

• Beneficial impact– decomposers of dead plants and animals– sources of antibiotics, alcohol, organic acids,

vitamins– used in making foods and in genetic studies

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Kingdom Protista• Algae• Protozoa

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Algae• Photosynthetic organisms• Kelps, seaweeds, euglenids, green algae, diatoms,

dinoflagellates, brown algae, and red seaweeds• Microscopic forms are unicellular, colonial,

filamentous.• Macroscopic forms are colonial and multicellular.• Contain chloroplasts with chlorophyll and other

pigments• Cell wall• May or may not have flagella

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Algae• Most are free-living in fresh and marine water –

plankton.• Provide basis of food web in most aquatic habitats• Produce large proportion of atmospheric O2

• Dinoflagellates can cause red tides and give off toxins that cause food poisoning with neurological symptoms.

• Classified according to types of pigments and cell wall

• Used for cosmetics, food, and medical products

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Protozoa• 65,000 species• Vary in shape, lack a cell wall • Most are unicellular; colonies are rare• Most are harmless, free-living in a moist habitat• Some are animal parasites and can be spread by insect

vectors.• All are heterotrophic.• Feed by engulfing other microbes and organic matter

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Protozoa• Most have locomotor structures – flagella, cilia, or

pseudopods.• Exist as trophozoite - motile feeding stage• Many can enter into a dormant resting stage when

conditions are unfavorable for growth and feeding – cyst.

• All reproduce asexually, mitosis or multiple fission; many also reproduce sexually – conjugation.

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Protozoan Identification• Classification is difficult because of diversity.• Simple grouping is based on method of motility,

reproduction, and life cycle.1. Mastigophora – primarily flagellar motility, some flagellar

and amoeboid; sexual reproduction; cyst and trophozoite2. Sarcodina – primarily ameba; asexual by fission; most are

free-living3. Ciliophora – cilia; trophozoites and cysts; most are free-

living, harmless 4. Apicomplexa – motility is absent except male gametes;

sexual and asexual reproduction; complex life cycle – all parasitic

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Important Protozoan Pathogens• Pathogenic flagellates

– Trypanosomes – Trypanosoma• T. brucei – African sleeping sickness• T. cruzi – Chaga’s disease; South America

• Infective amebas– Entameba histolytica – amebic dysentery;

worldwide

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Parasitic Helminths• Multicellular animals, organs for reproduction,

digestion, movement, protection• Parasitize host tissues• Have mouthparts for attachment to or digestion of

host tissues• Most have well-developed sex organs that produce

eggs and sperm.• Fertilized eggs go through larval period in or out

of host body.

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Major Groups of Parasitic Helminths1. Flatworms – flat, no definite body cavity;

digestive tract a blind pouch; simple excretory and nervous systems• cestodes (tapeworms)• Trematodes or flukes, are flattened ,

nonsegmented worms with sucking mouthparts.2. Roundworms (nematodes)- round, a complete

digestive tract, a protective surface cuticle, spines and hooks on mouth; excretory and nervous systems poorly developed

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Helminths

• 50 species parasitize humans.• Acquired though ingestion of larvae or eggs

in food; from soil or water; some are carried by insect vectors

• Afflict billions of humans

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Helminth Classification and Identification

• Classify according to shape, size, organ development, presence of hooks, suckers, or other special structures, mode of reproduction, hosts, and appearance of eggs and larvae

• Identify by microscopic detection of adult worm, larvae, or eggs

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Distribution and Importance of Parasitic Worms

• Approximately 50 species parasitize humans.• Distributed worldwide; some restricted to

certain geographic regions with higher incidence in tropics

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