Foundations in Microbiology

Seventh Edition

Chapter 5

Eukaryotic Cells and Microorganisms

Lecture PowerPoint to accompany

Talaro

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2

5.1 The History of Eukaryotes

• They first appeared approximately 2 billion years ago

• Evidence suggests evolution from prokaryotic organisms by symbiosis

• Organelles originated from prokaryotic cells trapped inside them

3

4

5

6

7

5.2 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 prokaryotic 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

8

Figure 5.4 Structure and locomotion in ciliates

9

10

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

11

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

12

External Boundary Structures

• Cytoplasmic (cell) membrane– Typical bilayer of phospholipids and proteins– Sterols confer stability– Serves as selectively permeable barrier in

transport– Eukaryotic cells also contain membrane-bound

organelles that account for 60-80% of their volume

13

5.3 Internal Structures• Nucleus

– Compact sphere, most prominent organelle of eukaryotic 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

Figure 5.5 The nucleus

14

Figure 5.6 Mitosis

15

16

Internal Structures• Endoplasmic reticulum – two types:

– Rough endoplasmic reticulum (RER) – originates from the outer membrane of the nuclear envelope 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

Figure 5.7 Rough endoplasmic reticulum

17

18

Internal Structures• Golgi apparatus

– Modifies, stores, and packages proteins– Consists of a stack of flattened sacs called cisternae– 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

Figure 5.8 Golgi apparatus

19

20

Figure 5.9

nucleus RER Golgi vesicles secretion

21

Internal Structures• Lysosomes

– Vesicles containing enzymes that originate from Golgi apparatus – Involved in intracellular digestion of food particles and in

protection against invading microbes– Participate in digestion

• Vacuoles– Membrane bound sacs containing particles to be digested,

excreted, or stored

• Phagosome – vacuole merged with a lysosome

22

Figure 5.10

23

Internal Structures

• Mitochondria– Function in energy production– Consist 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 prokaryotic ribosomes

Figure 5.11 Structure of mitochondrion

24

25

Internal Structures• Chloroplast

– Convert the energy of sunlight into chemical energy through photosynthesis

– Found in algae and plant cells– Outer membrane covers inner membrane folded

into sacs, thylakoids, stacked into grana– Larger than mitochondria– Contain photosynthetic pigments– Primary producers of organic nutrients for other

organisms

26

Figure 5.12

27

Internal Structures

• Ribosomes– Composed of rRNA and proteins– Scattered in cytoplasm or associated with RER– Larger than prokaryotic ribosomes– Function in protein synthesis

28

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

Figure 5.13 A model of the cytoskeleton

29

30

31

32

Survey of Eukaryotic Microbes

• Fungi

• Algae

• Protozoa

• Parasitic worms

33

5.4 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

34

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

35

Figure 5.15

36

Figure 5.16c

37

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

Figure 5.17 Nutritional sources for fungi

38

39

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

40

Figure 5.18

41

Fungal Reproduction• Primarily through spores formed on reproductive

hyphae

• Asexual reproduction – spores are formed through budding or mitosis; conidia or sporangiospores

42

Figure 5.19

43

Fungal Reproduction

• Sexual reproduction – spores are formed following fusion of two different strains and formation of sexual structure– Zygospores, ascospores, and basidiospores

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

44

Figure 5.20 Formation of zygospores

45

Figure 5.21 Production of ascospores

46

Figure 5.22 Formation of basidiospores in a mushroom

47

Fungal Classification

Kingdom Eumycota is subdivided into several phyla based upon the type of sexual reproduction:

1. Zygomycota – zygospores; sporangiospores and some conidia

2. Ascomycota – ascospores; conidia

3. Basidiomycota – basidiospores; conidia

4. Chytridomycota – flagellated spores

5. Fungi that produce only Asexual Spores (Imperfect)

48

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

49

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

50

51

5.5 Kingdom Protista

• Algae - eukaryotic organisms, usually unicellular and colonial, that photosynthesize with chlorophyll a

• Protozoa - unicellular eukaryotes that lack tissues and share similarities in cell structure, nutrition, life cycle, and biochemistry

52

53

Algae• Photosynthetic organisms• 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

54

55

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

56

57

Protozoa• Diverse group of 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 – lack chloroplasts• Cytoplasm divided into ectoplasm and endoplasm• Feed by engulfing other microbes and organic matter

58

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

59

Figure 5.27

60

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

reproduction, and life cycle1. Mastigophora – primarily flagellar motility, some flagellar

and amoeboid; sexual reproduction

2. Sarcodina – primarily amoeba; asexual by fission; most are free-living

3. 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

61

Figure 5.28

62

Figure 5.29

63

Figure 5.30

64

Figure 5.31

65

Important Protozoan Pathogens

• Pathogenic flagellates– Trypanosomes – Trypanosoma

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

• Infective amoebas– Entamoeba histolytica – amebic dysentery;

worldwide

66

Figure 5.32

67

Figure 5.33

68

69

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

70

Major Groups of Parasitic Helminths

1. 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

71

Helminths

• Acquired through ingestion of larvae or eggs in food; from soil or water; some are carried by insect vectors

• Afflict billions of humans

72

Figure 5.34 Parasitic Flatworms

73

Figure 5.35

74

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

75

Distribution and Importance of Parasitic Worms

• Approximately 50 species parasitize humans

• Distributed worldwide; some restricted to certain geographic regions with higher incidence in tropics