topic 2 review
TRANSCRIPT
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
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!!!