Module 2: Introduction to general microbiology: Bacterial structure & morphology

length: 2 um - 8 um

diameter: 0.2 - 2.0 um

size of bacteria

Capsule

1

Cell wall

2

Plasma membrane

3

Cytoplasm

4

Ribosomes

5

Plasmid

6

Pili

7

Bacterial Flagellum

8

Nucleoid (circular DNA)

9

glycocalyx

• General term used for substances that surround the cells

• A coating that covers the outside of prokaryotic cells that provides a protective coat

• It is viscous (sticky), gelatinous polymer external to the cell wall, composed of polysaccharide , polypeptide or both

• Important component of Biofilms

Function:

• Extracellular polymeric substance (EPS)

  • a glycocalyx that helps cells in a biofilm attach to their target environment and to each other

  • Protects cells within it and facilitates communication

  • Enables the cell to survive by attaching to various surfaces in natural environment

slime layer

if the substance is unorganized and only loosely attached to the cell wall, the glycocalyx

capsule

• if the substance is organized and firmly attached to the cell wall

• It is important in contributing to bacterial virulence.

• often protect pathogenic bacteria from phagocytosis by the cells of the host

  • E.g. Bacillus anthracis - capsule of D-glutamic acid

  • Streptococcus pneumoniae

  • Klebsiella

cell wall

• Prevent the bacterial cells from rupturing

• Helps maintain the shape of the cell

• Point of anchorage for flagella

• Contributes to the ability of some species to cause disease

• Site of action of some antibiotics (e.g. penicillin)

• Chemical composition is used to differentiate major types of bacteria (Gram-positive, Gram-negative)

• Composed of peptidoglycan (murein)

plasma membrane

• Thin structure lying inside the cell wall and enclosing the cytoplasm of cell

• Consists primary of phospholipids

• Look like two-layered structures (lipid bilayer)

• Serve as a selective barrier through which materials enter and exit the cell (selective permeability)

• Breakdown of nutrients and the production of energy

flagella

• long filamentous appendages that propel bacteria

• Some bacteria have the capability to move in various patterns

atrichous

bacteria that lacks flagella

• peritrichous

• monotrichous and polar

• lophotrichous and polar

• amphitrichous and polar

arrangement of bacterial flagella

peritrichous

• flagella are distributed over the entire cell

• 0.5 μm

monotrichous and polar

• a flagellum at one pole

• 0.8 μm

Lophotrichous and polar

• many flagella coming from one pole

• turf of flagella

• 1.5 μm

Amphitrichous and polar

• flagella at both poles of the cell

• 4 μm

• amphi = 2

H antigen

• flagellar protein; useful for distinguishing among serovars or variations

• Example: there are at least 50 different ◦H antigens for E. coli. Those serovars identified as E. coli O157:H7 are associated with foodborne epidemics

spirochetes

• group of bacteria that have unique structure and motility (spiral motion)

• They move by means of axial filaments or endoflagella

  • E.g. Treponema pallidum – causative agent of syphilis

  • Borrelia burgdorferi – causative agent of Lyme disease

fimbriae and pili

Hair-like appendages that are shorter, straighter, and thinner than flagella

fimbriae

the bacterial cell or can be evenly distributed over the entire surface of the cell

pili

• usually longer than fimbriae and number only one or two per cell

  • involved in motility and DNA transfer

• Some are used to bring bacteria together, allowing the transfer of DNA from one cell to another (conjugation)

sex pilus

• Pili that will transfer the DNA from one bacterium to another (conjugation) 

cytoplasm

Refers to the substance of the cell inside the plasma membrane

• nucleoid (containing DNA)

• ribosomes

• inclusions

• plasmid

major structures in cytoplasm

nucleoid

• Contains the bacterial chromosome

• This is the cell’s genetic information

• Bacterial chromosomes are not surrounded by a nuclear envelope and no histones

plasmid

• Small, usually circular, double stranded DNA molecules

• These are extrachromosomal genetic elements (not connected to main bacterial chromosome)

• Replicate independently

ribosomes

• Where protein synthesis takes place

• Prokaryotic ribosomes are called 70S ribosomes (80S ribosomes in eukaryotes)

• S = Svedberg unit = unit of size

• Subdivided into 2 subunits that is targeted by some antibiotics:

  • 30S

  • 50S

inclusions

• Several kinds of reserve deposits in the cytoplasm

endopores

• Specialized “resting” cells formed by some gram-positive bacteria (genera Clostridium and Bacillus) when essential nutrients are depleted

• Highly durable dehydrated cells with thick walls and additional layers

• can survive extreme heat, lack of water, and exposure to many toxic chemicals and radiation

• Cannot multiply

• Can remain dormant for thousand of years

• Not a means of reproduction (one vegetative cell forms a single endospore)

• Importance in food industry because of resistance to processes that normally kill vegetative cells

• Most vegetative cells can be killed with temp above 70 C

• Endospores can survive in boiling water for several hours or more (thermophilic/heat-loving)

vegetative cells

• State of bacteria wherein they can multiply through binary fission

sporulation / sporogenesis

From vegetative state to endospores

germination

endospores to vegetative cells

dipicolinic acid

a large amount of an organic acid contained in endospore; protects the endospore DNA against damage

a. cocci or spherical bacteria

1. diplococci

2. streptococci

3. staphylococci

4. sarcinae

5. tetrads

b. bacilli or rod-shape bacteria; may be cigar-like or straw=like

1. diplobacilli

2. streptobacilli

3. coccobacilli

4. bacilli with rounded ends

5. bacilli with square ends

6. filamentous bacilli

c. helical / spiral (one to two twist)

1. vibroid / comma-shape

2. spirilla

3. sprirochetes

other shape

• genus stella

• halophilic archaea

• triangular shapes

shapes of bacteria

diplococci

round bacteria in pairs; remain in pairs after dividing

streptococci

cocci in chains

staphylococci

cocci in cluster resembling bunch of grapes

sarcinae

in groups of 8 in cubical pockets (octads)

tetrads

divide in 2 planes and remain in groups of 4

diplobacilli

in paired bacilli

streptobacilli

rods in chain

coccobacilli

short rods

filamentous bacili

usually do not separate and tend to form “long threads”

vibroid / comma-shape

(less than one complete twist); curved rods

spirilla

– loosely curved cells; have helical shape like a cork-screw and fairly rigid bodies with flagella

spirochetes

– tightly coiled form; flexible with axial filaments

genus stella

star-shaped

halophilic archaea

flat rectangular shape