Topic 2 review

Topic  2  Bacteria  

Bacterial  Morphology  •  Morphology:  

–  Spherical  =  Coccus  –  Rod  shaped  =  Bacillus  –  Comma  Shaped  =  Vibrio  –  Spiral  =  Spirillium  –   Varied  shape  =  Pleiomorphic  

•  Generally  not  a  good  predictor  of  physiology,  ecology,  or  phylogeny  

•  Morphology  may  be  determined  by  selecBve  forces  –  nutrient  uptake  efficiency  (surface-­‐to-­‐volume  raBo)  –  spirals  allow  efficient  swimming  in  viscous  or  

turbulent  fluids  (i.e.  near  surfaces)  –  gliding  moBlity  (filaments)  

•  Bacteria  can  also  assume  mulBcellular  organizaBons  –  hyphae  (branching  filaments  of  cells)  –  mycelia  (tuNs  of  hyphae)  –  trichomes  (smooth,  unbranched  chains  of  cells)  

Cell  Sizes  •  Prokaryotes  are  0.2  μm  to  >  

700  μm  in  diameter  –  most  rod-­‐shaped  bacteria  between  0.5  μm-­‐4.0  

μm  wide  and  1-­‐15  μm  long  –  very  few  “large” prokaryotes  –  ExcepBons:  

•  Thiomargarita namibiensis: up to 700 μm in diameter"

•  Epulopiscium fishelsoni: 200‒700 μm x 80 μm!  

•  EukaryoBc  cells  range  from  10  μm  to  >200  μm  

•  Minimum  size  simply  due  to  minimum  space  requirements  for  genome,  proteins,  ribosomes  –  Diameters  <  0.15  μm  

unlikely  –  “Very  small”  cells  common  

in  open  marine  environments  

•   Advantages  to  being  small:  •   Higher  surface-­‐to-­‐volume  raBo  

• greater  rate  of  nutrient/waste  exchange  per  unit  volume  • supports  higher  metabolic  rate  • supports  faster  growth  rate,  faster  evoluBon  

What  Is  in  the  Cytoplasm  

•  inclusion  bodies  may  also  be  present  sulfur  globules:  sulfur  storage  for  energy  polyhydroxybutyrate  granules:  carbon  storage  gas  vesicles:  buoyancy  control  carboxysomes:  locaBon  of  carbon  fixaBon  reacBons  (RUBISCO)  magnetosomes:  organelle  associated  with  direcBon  finding  

How  does  DNA  compress  within  the  nucleoid  of  bacteria?  

•  several  mechanisms  to  reduce  space  –  use  of  caBons  (Mg2+,  K+,  Na+)  to  shield  negaBve  charges  on  sugar-­‐phosphate  (PO4-­‐)  backbone  

–  small,  posiBvely  charged  proteins  bind  to  the  chromosome  to  maintain  condensed  structure  

–  topoisomerases  modify  structure  of  DNA  to  enable  “supercoiling”  

•  No  membrane  surrounds  the  nucleoid  •  No  histone  proteins  (like  those  found  in  Archaea  and  Eukaryotes)  

Cytoskeleton  Proteins  •  FtsZ  –  Forms  Z  ring,  is  used  to  divide.  

–   If  you  didn't  have  this,  you  would  become  a  very  long  cell  with  no  mechanism  to  divide.    

–  Rips  apart  the  cell  wall  and  then  glues  it  back  together,  facilitates  cell  division.    

–  HOMOLOG  TO  TUBULIN.  •  MreB  -­‐  governs  the  shape  of  bacterial  cell.    

–  If  you  are  lacking  MreB  at  all,  you  will  be  cocci  shaped.  

–  If  you  do  have  MreB  then  you  will  polymerize  MreB  protein  that  acts  like  a  spring  that  will  support  the  shape  of  the  bacteria.    

–  HOMOLOG  TO  ACTIN.    •  ParM  -­‐  polymerize  (need  ATP)  to  push  the  

plasmids  and  chromosomes  to  either  side  so  the  cell  can  divide.  –  Alaches  to  ParR  

Cell  Envelope  •  All layers surrounding the cytoplasm of cells, which includes:"

–  Cell membrane (plasma membrane):"•  Bilayer composed of a phospholipid bilayer (glycerol w/ fatty acids attatched with

ESTER linkages) with embedded proteins and hopinoids"•  Separates internal from external enviro (fluid mosaic model)"•  Capturing energy"

–  electron transport chains create proton motive force (PMF)"–  can be used for respiration/photosynthesis "–  can be used to derive energy for motion (flagella)"

•  Holding sensory systems (Chemotaxis)"–  embedded proteins can detect environment changes, alter gene expression in response"

–  Cell wall"•  gives cells their shape. Without  it,  cell  can’t  resist  osmoBc  pressure  changes"•  protects from osmotic lysis/mechanical forces"•  a matrix of crosslinked strands of peptidoglycan subunits"•  Composed of Peptidoglycan subunits of NAG and NAM"

–  Crosslinked by Petptide Crosslink or Peptidoglycine Interbridge "

–  Outer membrane (if present)  

How  do  items  cross  the  plasma  membrane?  

•  O2  and  CO2  are  small  and  can  diffuse  across  readily  

•  H2O  is  helped  across  by  aquaporin  protein  channels  (osmosis)  

•  Facilitated  diffusion  and  co-­‐transport:    –  protein  channel  moves  parBcles  WITH  a  

concentraBon  gradient    –  Co-­‐transport  can  be  sym  (molecules  going  to  

the  same  side)  or  anB  (molecules  going  to  opposite  sides)  

–  no  energy  •  AcBve  transport  

–  protein  transporter  moves  parBcles  AGAINST  a  concentraBon  gradient  

–  requires  energy  –  Includes  protein  secreBon  =  shipping  

proteins    outside  the  cell  

Cell  Wall  FormaBon  

Breaking  the  Cell  Wall  

•  Lysozyme  cleaves  backbone  and  lysostaphin  cleaves  pepBdogylcine  interbridge  

•  β-­‐lactam  anBbioBcs  –  prevent  pepBdoglycan  crosslinking  

•  Ex  penicillin    –  Inhibits FtsI transpeptidation

•  AnBbioBc  Resistance  –  Some bacteria can produce an enzyme to destroy the critical β-lactam ring

structure"–  second drug must be added to inhibit the enzyme"

Two  Types  of  Cell  Walls  •  Gram  PosiBve  

–  thick  outer  layer  of  pepBdoglycan  –  narrow  periplasmic  space  –  negaBvely  charged  teichoic  acids  in  the  

pepBdoglycan  •  Gram  NegaBve    

–  very  thin  layer  of  pepBdoglycan  –  periplasmic  space  of  varying  width    –  outer  membrane  composed  of  lipopolysaccharide  (LPS)  

•  Composed  of  lipid  A    core  polysacharide    varying  O  chain  

How  do  nutrients  get  through  the  cell  wall?  

•  Gram-­‐posiBve  pepBdoglycan  layer  has  large  pores  throughout  its  matrix  

•  Gram-­‐negaBve  cell  has  porin  and  TonB  proteins  in  its  outer  membrane    –  transfer  molecules  into  the  

periplasmic  space  –  How  can  molecules  get  out  of  a  

Gram-­‐negaBve  cell’s  periplasmic  space?  

•  some  move  from  the  periplasm  to  outside  directly  (these  are  known  as  autotransporters  and  are  rare  

•  some  use  single-­‐step  (never  entering  the  periplasm)  transport  systems  

Cell  Movement  •  Flagella  (Fillament-­‐Hook-­‐Basal  Body):  

–  MONOTRICHOUS  =  One  flagella    –  AMPHITRICHOUS  =  Two  flagella  –  LOPHOTRICHOUS  =  mulBple  but  polarized  –  PERITRICHOUS  =  mulBple  from  all  ends  

•  Nonflagellar  MoBlity  –  Gliding  moBlity    

•  smooth  sliding  over  a  surface,  not  well  understood    •  e.g.  Myxobacteria,  Cyanobacteria  

–  Twitching  moBlity  •  slow,  jerky  process  using  pili  that  extend,  alach  to,  and  pull  along  a  surface    

Adherence Molecules  •  allow  cells  to  sBck  to  surfaces  •  pili  (s.  pilus),  fibers  of  pilin  

protein,  possess  other  proteins  on  their  Bps  for  sBcking  –  Ones  for  adherence  are  called  

Fimbriae  •  Some  microbes  will  use  an  

extension  of  the  cell  envelope  Bpped  by  a  “holdfast”  of  polysaccharides  –  Called  a  Stalk  –  Provide  extra  surface  area  for  

nutrient  absorpBon    

Capsules  and  S-­‐Layers  •  Capsules:  

–  Thick  layer  of  polysaccharides  surrounding  some  cells  –  provide  adhesion,  defense  against  host  immunity,  protecBon  against  

desiccaBon  (biofilms)  •  Surface  Arrays  

–  crystalline  array  of  interlocking  proteins  –  can  protect  a  cell  against  predaBon  or  infecBon  with  bacteriophages  –  found  in  both  Gram-­‐posiBve  and  Gram-­‐negaBve  cells  

Bacterial  Taxonomy  •  Are  named  by  Species  and  Genus  •  ClassificaBon  depends  on  many  

features:  –  DNA  sequence  data  –  size/shape  –  Gram  type  –  colony  morphology  –  presence  of  structures  such  as  

capsules/endospores  –  physiologic/metabolic  traits  

•  Once  classified,  they  are  put  into  the  database  of  the  World  Federa?on  for  Culture  Collec?ons    –  Become  a  “Type  strain”  is  a  referenced  

specimen  deposited  in  a  culture  repository.  

But  MOST  can  not  be  cultured!!!