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Chapter 2.- Bacterial Classification, Structure, and Replication

Processes of Life

• Growth

• Reproduction

• Responsiveness

• Metabolism

Examples of types of cells

Figure 3.1

Prokaryotic and Eukaryotic Cells: An Overview

• Prokaryotes

– Lack nucleus

– Lack various internal structures bound with phospholipid membranes

– Are small, ~1.0 µm in diameter

– Have a simple structure

– Composed of bacteria and archaea

Typical prokaryotic cell

Figure 3.2

Prokaryotic and Eukaryotic Cells: An Overview

• Eukaryotes

– Have nucleus

– Have internal membrane-bound organelles

– Are larger, 10–100 µm in diameter

– Have more complex structure

– Composed of algae, protozoa, fungi, animals, and plants

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Typical eukaryotic cell

Figure 3.3

Approximate size of various types of cells

Figure 3.4

General Characteristics of Prokaryotic Organisms

• Prokaryotes

– Most diverse group of cellular microbes

– Habitats

• From Antarctic glaciers to thermal hot springs

• From colons of animals to cytoplasm of other prokaryotes

• From distilled water to supersaturated brine

• From disinfectant solutions to basalt rocks

– Only a few capable of colonizing humans and causing disease

Typical prokaryotic morphologies

Figure 11.1

General Characteristics of Prokaryotic Organisms

• Arrangement of Prokaryotic Cells

– Result from two aspects of division during binary fission

• Planes in which cells divide

• Separation of daughter cells

Arrangements of cocci

Figure 11.6

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Arrangements of bacilli

Figure 11.7

Bacterial shapes and arrangements

Figure 3.12

External Structures of Bacterial Cells

• Glycocalyces

– Gelatinous, sticky substance surrounding the outside of the cell

– Composed of polysaccharides, polypeptides, or both

External Structures of Bacterial Cells

• Two Types of Glycocalyces

– Capsule

• Composed of organized repeating units of organic chemicals

• Firmly attached to cell surface

• May prevent bacteria from being recognized by host

– Slime layer

• Loosely attached to cell surface

• Water soluble

• Sticky layer allows prokaryotes to attach to surfaces

Example of Capsule

Figure 4.20

Glycocalyces

Figure 3.5

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External Structures of Bacterial Cells

Animation: Motility

External Structures of Bacterial Cells

• Flagella

– Are responsible for movement

– Have long structures that extend beyond cell surface

– Are not present on all bacteria

External Structures of Bacterial Cells

• Flagella

– Structure

• Composed of filament, hook, and basal body

• Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins

External Structures of Prokaryotic Cells

Animation: Flagella: Structure

Proximal structure of bacterial flagella

Figure 3.6

Basic arrangements of bacterial flagella

Figure 3.7

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External Structures of Bacterial Cells

Animation: Flagella: Arrangement

External Structures of Bacterial Cells

Animation: Flagella: Spirochetes

Axial filament

Figure 3.8

External Structures of Bacterial Cells

• Flagella

– Function

• Rotation propels bacterium through environment

• Rotation reversible; can be counterclockwise or clockwise

• Bacteria move in response to stimuli (taxis)– Runs

– Tumbles

Motion of a peritrichous bacterium

Figure 3.9

External Structures of Bacterial Cells

Animation: Flagella: Movement

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External Structures of Bacterial Cells

• Fimbriae and Pili

– Rod-like proteinaceous extensions

External Structures of Bacterial Cells

• Fimbriae

• Sticky, bristlelike projections

• Used by bacteria to adhere to one another, to hosts, and to substances in environment

• Shorter than flagella

• Serve an important function in biofilms

Fimbriae

Figure 3.10

External Structures of Prokaryotic Cells

• Pili

– Tubules composed of pilin

– Also known as conjugation pili

– Longer than fimbriae but shorter than flagella

– Bacteria typically only have one or two per cell

– Mediate the transfer of DNA from one cell to another (conjugation)

Pilus

Figure 3.11

Bacterial Cell Walls

• Provide structure and shape and protect cell from osmotic forces

• Assist some cells in attaching to other cells or in resisting antimicrobial drugs

• Can target cell wall of bacteria with antibiotics• Give bacterial cells characteristic shapes• Composed of peptidoglycan• Scientists describe two basic types of bacterial cell

walls– Gram-positive and Gram-negative

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Comparison of structures of glucose, NAG, and NAM

Figure 3.13

Bacterial Cell Walls

• Gram-positive Bacterial Cell Walls

– Relatively thick layer of peptidoglycan

– Contain unique polyalcohols called teichoic acids

– Appear purple following Gram staining procedure

– Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation

Gram-positive bacteria

Figure 3.15a

Prokaryotic Cell Walls

• Gram-Negative Bacterial Cell Walls

– Have only a thin layer of peptidoglycan

– Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)

– May be impediment to the treatment of disease

– Appear pink following Gram staining procedure

Gram-negative bacteria

Figure 3.15b

Gram Staining

Gram +Gram -

Figure 4.17

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Acid-fast Cells

• Gram positive cells

• Extra stuff in cell wall– Mycolic acid – a waxy lipid, up to 60% of cell wall

– Resistant to dessication, antibiotics

• Special staining procedure called acid-fast staining

• Mycobacteria

Acid-fast Staining

Figure 4.18

Bacteria without Cell Walls

• Mycoplasma

– Sterols in cell membrane

LPS

• Union of lipid with sugar

• Lipid portion known as lipid A

– Also known as endotoxin

– Dead cells release lipid A when cell wall disintegrates

– May trigger fever, vasodilation, inflammation, shock, and blood clotting

– Can be released when antimicrobial drugs kill bacteria

Periplasmic Space

• Located between outer membrane and cell membrane

– Contains peptidoglycan and periplasm

– Contains water, nutrients, and substances secreted by the cell, such as digestive enzymes and proteins involved in transport

Bacterial Cytoplasmic Membranes

• Structure– Referred to as phospholipid bilayer

• Composed of lipids and associated proteins

– Fluid mosaic model describes current understanding of membrane structure

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Structure of prokaryotic cytoplasmic membrane

Figure 3.16

Bacterial Cytoplasmic Membranes

• Function– Energy storage

– Harvest light energy in photosynthetic bacteria

– Selectively permeable

– Naturally impermeable to most substances

– Proteins allow substances to cross membrane

– Maintain concentration and electrical gradient

Electrical potential of a cytoplasmic membrane

Figure 3.17

Bacterial Cytoplasmic Membranes

• Function

– Passive processes

• Diffusion

• Facilitated diffusion

• Osmosis

Passive processes of movement

Figure 3.18

Osmosis

Figure 3.19

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Effects of solutions on cells

Figure 3.20

Prokaryotic Cytoplasmic Membranes

• Function

– Active processes

• Active transport

– Group translocation

• Substance chemically modified during transport

Mechanisms of active transport

Figure 3.21

Bacterial Cytoplasmic Membranes

Animation: Active Transport: Overview

Bacterial Cytoplasmic Membranes

Animation: Active Transport: Types

Group translocation

Figure 3.22

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Cytoplasm of Bacteria

• Cytosol

– Liquid portion of cytoplasm

• Inclusions

– May include reserve deposits of chemicals

• Endospores

– Unique structures produced by some bacteria that are a defensive strategy against unfavorable conditions

The formation of an endospore

Figure 3.24

General Characteristics of Prokaryotic Organisms

• Endospores– Produced by Gram-positive Bacillus and

Clostridium

– Each vegetative cell transforms into one endospore

– Each endospore germinates to form one vegetative cell

– Defensive strategy against unfavorable conditions

– Concern to food processors, health care professionals, and governments

Spore Structure

Outer Spore Coat(Exosporium)

Spore Coat

Outer Membrane

Cortex

Inner Membrane

Core

Spore Wall

Locations of endospores

Figure 11.8

Cytoplasm of Prokaryotes

• Nonmembranous Organelles

– Ribosomes

• Sites of protein synthesis

– Cytoskeleton

• Plays a role in forming the cell’s basic shape

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A simple helical cytoskeleton

Figure 3.25

General Characteristics of Prokaryotic Organisms

• Reproduction of Prokaryotic Cells

– All reproduce asexually

– Three main methods

• Binary fission (most common)

• Snapping division

• Budding

General Characteristics of Prokaryotic Organisms

Animation: Bacterial Growth: Overview

Binary fission

Figure 11.2

Snapping division, a variation of binary fission

Figure 11.3

Budding

Figure 11.5

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Nomenclature

• Genus– It is always a noun– It is written first– It is capitalized

• Species– It is usually an adjective– It is written second– It always contains lowercase letters

• Genus + species is printed in italics or underlined

• Example:– Escherichia coli, E. coli

The End

Chapter 2.- Bacterial Classification, Structure, and Replication