WEEK 6

BMY3101-1 MICROBIOLOGY I

WHAT HAVE I LEARN?

This week we move on to next topic that is the Introduction to Prokaryotes. We have covered the whole chapter in 1 hour 30 minutes. With some addition explanation from Dr, i am able to understand more about this chapter. We study about the external structure in this class before going to the internal structure of prokaryote. Dr gives some external knowledge before the class start. For sterilization,  we use UV, autoclave or Bunsen burner and also filter sterilize technique. Filter sterilize technique uses substances filter through membrane filter of 0.25- 0.45 micrometer. For example the antibiotic. Antibiotic is added into medium to ensure that there is no growth of bacteria. When we grow fungus but there is contamination of bacteria, antibiotic is added to control.

Prokaryotes are group of organisms that lack of nucleus ( = karyon) and other membrane bounded organelles. Bacteria and archeae are prokaryote. 

Size 

0.2 to 2.0 micrometer in diameter and 2 to 8 micrometer in length.

Shapes

Coccus  - sphere
Bacillus - rod shaped
Spiral    

Arrangement

Cocci: diplococci,staphylococci and streptococci

Bacilli: diplobacilli and streptobacilli

Spiral: vibrio, spirillum and spirochete

There are also addition shape:

Unusual

- star-shaped

- square

- triangular

Pleomorphic

- within  a population, they can dorm various shapes

- they can change shape to adapt the extreme temperature

No fixed shape

- cellwall-less : mycoplasma/ ureaplasma

* microorganisms which have a larger size:

- bigger adaptivality to environment 

- store more food 

mycoplasma are the smallest bacteria, 0.3 microns.

Cell structure of bacteria

Cell wall and membrane structure of prokaryote 

Structure external to the cell wall

• Glycocalyx
• flagella
• axial filaments
• fimbriae and pili

GLYCOCALYX

• surrond the cell
• made inside the cell and excreted to cell surface
• polysaccharides, polypeptides or both
• made of sugars called an extracellular polysaccharides ( EPS)                                *most of bacteria can produce EPS. Example: biofilm attach to surface in form of matrix, stick to each other

Function

• protection from phagocytosis
• attachment to various surface
• source of nutrients
• protect a cell against dehydation
• maintain the shape

Two cell surface layers

• capsules

- organized and firmly attach to cell wall

- distinct and gelatinous 

- antiphagocytic 

- protect from dehydration

• slime layer

- unorganized and loosely attached to the cell wall

FLAGELLA

• Treadlike, locomotor appendages extending outward from plasma membrane and cell wall
• made of protein flagellin and consistes of a filament and basal region

Function

• motility and swarming behavior
• attachment to surfaces
• may be virulence factors

Arrangement of flagella

Flagella strcuture 

Gram + organisms have 2 rings ( 1 in cell wall, 1 in cell membrane)

Gram - organisms have 4 rings ( 2 in cell wall, 2 in cell membrane )

Types of motility

- when there is harmful to bacteria ( antibiotic, chemical), they have to run away

• "run" or "swim"

Moves in one direction for a length of time

• 'tumbles"

runs interrupted by periodic abrupt, random changes in direction

# when hit smtg

• "swarm"

rapid wavelike movement

AXIAL FILAMENT ( endoflagella)

• Bundles of fibrils that arise at the ends of the cell beneath the outer sheath
• spiral around the cell
• present in a spirochetes group of bacteria 
• eg: Treponema pallidum and Borrelia burgdorferi 

FIMBRIAE AND PILI

• Hairlike appendages that are shorter, straighter and thinner than flaggela
• consists of pilin
• used for attachment

Fimbriae 

• occur at poles of bacterial cell
• evenly distributed over entire surface of cell
• few to hundred per cell

Pili

• longer than fimbriae
• one or two per cell
• for preparation of transfer of DNA 
• sex pili ( transfer of plasmid)

Cell wall

• surround cytoplsmic membrane 
• not regulatory structure
• ❌ selectively permeable
• can fit and pass through
• composed of macromolecular network called peptidoglycan ( murein)
• peptidoglycan consists of repeating dissacharides
• dissacharides: N- acetylglucoseamine (NAG) and N- acetylmuramic acid (NAM)
• alternating NAM and NAG linked in row - by glycosidic ( 𝞫 1,4) bonds                                                                             adjacent - by peptide bonds

Function

• prevent from rupturing when water pressure inside is greater than outside
• contribute pathogenicity
• classification
• maintain shape - rigid wall compensades for flexibility of membrane
• provide rigid platform ( a point of anchorage ) for surface appendages ( flagella, pili, cilia emanate from wall and extend beyond)
• counters effects of osmotic pressure → strength of cell wall keep cell from bursting when osmotic intracellular > extracellular

Gram positive 

• have thick layer of peptidoglycan
• lies between plasma membrane and cell wall is smaller than gram - 
• periplasm have only few protein
• enzyme secreted called exoenzyme → aids in degration of large nutrient

Teichoic acid

• primarily of an alcohol ( such as glycerol or ribitol) & phosphate 
• negatively charged (-)
• provide much more of wall's antigen specificity
• make gram positive acidic
• cell walls ❌ degrades easily

2 types → lipoteichoic acid ( spans the peptidoglycan layer & linked to plasma membrane)

             → wall teichoic acid ( link to peptidoglycan layer)

↝ DON'T HAVE OUTER MEMBRANE

Gram negative

• one, less layers peptidoglycan → more susceptible to mechanical breakage
• peptidoglycan bonded to lipoprotein
• ❌ teichoic acid

peptidoglycan ↪ 10% of cell wall

                       ↪ bonded lipoprotein

                       ↪ located btw outer membrane and cytoplasmic membrane ( periplasmic                                   area) 

Periplasmic space

• high concentration of degrating enzyme
• large amount of transport proteins
• 20%- 40% of cell volume

↝ HAVE OUTER MEMBRANE 

• consists of lipoproteins, lipopolysaccharides ( LPS) , phospholipids and porins
• strong negative charge → evade phagocyctosis
• provide barrier for antibiotic ( penicillin ), lysozyme, detergent, heavily metals, bile salts, certain dyes.
• porins from channel permit passage of molecules such as nucleotides, dissacharides, peptides, aminoacids, vitamin B12 and iron

LPS

• ↦ polysaccharides portion called O polysaccharides ( composed by sugar)
• function as antigen
• useful for distinguish gram -
• role same as teichoic acid
• ↦ lipid portion called lipid A
• endotoxin
• toxic when in host's bloodstream or glastrointestine tract - cause fever and toxic shock

source: https://www.slideshare.net/shaniapasaoa/gram-positive-and-gram-negative

Unusual features of peptidoglycan 

↷ D- alanine & D- glutamic acid used

↷ N- acetylmuramic acid & diaminopimelic acid found in bacteria ( archeae or eukarya ❌)

↷ diaminopimelic ( DAP) found in gram - bacteria

↷ peptidoglycan layer are porous, unlike membrane

Atypical cell walls

• mycoplasma

↬ no cell wall, have very little wall materials

↬ membrane contains sterols - impart rigidity to membrane and protect them from osmotic        lysis

↬ smallest bacteria

↬ can pass through most bacterial filters

↬ eg: Mycoplasma pneumoniae  

• Chlamyddiaceae 

↬ 2 membrane ( like gram -)

↬ some genes for peptidoglycan synthesis found in genome

↬ obligate intracellular parasites

↬ non- replicative elementary body ( EB) form have extensive cross- linking in outer                  membrane proteins; analogous to spore 

Archaea

• lack peptidoglycan 
• some have cell walls consisting polusaccharides, glycoprotein or protein
• contain pseudopeptidoglycan ( psedomurein )
• most common wall type - paracrystalline surface layer ( s- layer)
• resistant to lysozyme and penicillin 

Pseudopeptidoglycan 

• 𝞫 ( 1,3 ) glycosidic bonds ( lysozyme insensitive )
• N- acetylglucosamine (NAG) & N- acetyltalosaminuronic acid (NAT)

S- layer

• surface / outermost layer forming " lipidless membrane"
• G+, G-
• composed of repeating subunits of protein or glycoprotein ( with hexagonal symmetry)
• protects against osmotic stress, PH and ezyme 
• aid in attachment
• inhibit phagocytosis