Bacterial Function/Differentiation Flashcards
What is the structure of a gram-positive bacterial cell wall?
many layers of peptidoglycan outside of plasma membrane
What is the structure of a gram-negative cell wall?
outer and inner plasma membranes w a thin layer of peptidoglycan sandwiched in between creating a periplasmic space
What is the process of Gram staining?
- heat fix cells which sticks bacteria to plate allowing washes without losing bacteria
- crystal violet stain attaches to peptidoglycan of gram+ and gram-
- iodine treatment forms with crystal violet creating large complexes, in gram+ this can be trappped in large peptidoglycan
layer, in gram- not much becomes trapped in thin layer - decolorization, large complexes in gram+ arent moved by alcohol but are washed away in gram-
- counter stain safranin, stains both but visible in gram- only due to large complexes present already in gram+
Why are most gram- bacteria pathogens?
outer membrane of cell wall allows protection from antibiotics
What are lipopolysaccharides?
present on outer membrane of cell wall of gram- bacteria
creates v drastic immune response in animal host causing a “toxic shock”
What is the S-layer?
present in gram+ and gram- bacteria
composed of glycoproteins
is a virulence factor as it allows bacteria to evade immune system
can be v quickly lost if bacteria does not need it in its environment
What is the capsule?
composed of polysaccharides
looser structure that forms a layer around bacterial cell
is a virulence factor as it allows attachment to surfacescan be v quickly lost if bacteria does not need it in its environment
What are fimbriae?
filamentous external protein structures that assist in surface attachment and movement in the environment
What are flagellum?
structure that assists in swimming
bacteria can move v fast allwoing easy escape or exploration of new niches
attached to bacteria via basal body that goes through both cell wall layers in gram-
made up of protein flagellin
Bacteria can be classified by their flagellation pattern. What types are there?
monotrichous = 1 flagellum at one pole
amphitrichous = 1 flagellum at both poles
lopotrichous = multiple flagella at one pole
peritrichous = many flagella all over bacterium
What is a unique property of transcription and translation in bacteria?
due to lack of nuclear envelop both transcription and translation can occur at the same location at the same time
What are the different methods of taxis bacteria?
- flagellar locomotion
- axial filament: similar to flagella but are located between the cell wall and outer sheath
- gliding motility: secrete slime to glide across surface
How do chemotaxis bacteria move in the presence of a chemoattractant?
will perform a biased random walk
if bacteria fell gradient increasing, the frequency of tumbles decreases so take longer straight runs
if gradeint decreases the number of tumbles increases so shorter runs
movement of bacteria is still random but statistically will eventually move upgradient
How does the flagellar motor pathway interact in the case of a random walk?
cheA is autophosphorylated which phosphorylates cheY which interacts with the flagellar motor
cheZ dephosphorylates cheY stopping it from interacting with the flagellar motor
this constant phosphorylation and dephosphorylation of cheY changes the flagellum from cw to ccw directions
How does the flagellar motor pathway interact in the case of a biased random walk?
the chemoreceptors cause cheA to stop being phosphorylated resulting in constant dephosphorylation cheY causing a consistent direction of the flagella motor
this results in fewer tumbles and longer runs
What rotations cause flagella to bundle or be pushed apart?
ccw rotation = flagella bundling
cw rotation = flagella pushed apart = tumble
What is the name for molecules which bacteria produce to sense cell density?
autoinducers
when a certain concentration is reached due to many bacteria present, the bacteria change from individual behaviours to group behaviours eg a cerain density of AHL causes bioluminescence
Metabolic outputs of one bacteria can be the metabolic input of another. What is an example of this?
lactic acid producers in the gut
What are some examples of using bacteria in bioremediation?
- clean up contaminated soils and groundwater
- bacteria utilise contaminants as source of foods and energy
- break down hazardous substances into less toxic or non-toxic substances
What is simple transport and what types are there?
transport of molecules by use of a transmembrane protein
driven by proton motive force
3 types: uniport, antiport, symport
What is group translocation?
transport of sugars by use of an energy rich compound eg PEP
multiple proteins involved
What is ABC transport?
= ATP-Binding Cassette
periplasmic proteins involved
energy comes form ATP
transport of sugars and amino acids
How do proteins signal to be excreted or integrated into the membrane?
signal peptides (15-20 amino acids at N-terminal)
signal is cleaved
In gram-negative bacteria, proteins must be secreted through both inner and outer membranes. What ways does this occur?
2 step: translocases through inner and outer membranes
1 step: proteins exported directly outside
Define a type III secretion system.
pathogenic bacteria use injectosomes to deliver toxins directly into host cells
what do most antibiotics produced by bacteria target?
inhibiting protein synthesis by targeting ribosomes
What are bacteriocins?
antimicrobial peptides that bind to receptors on sensitive cells and penetrate through plasma membrane
used to make the toxin-antitoxin system
How do scientists ensure that any microbes cannot survive outside the lab?
molecules present in the lab allow constitutive promotion of antitoxin which sequesters toxic
if bacteria escapes there is no promotion of antitoxin leading to cell ceath
What is a biofilm and its advantages?
a mass of metabolically quiescent cells attached firmly to a surface
- bacterial resistance: biofilms increase resistance to pathogens, immune system and antibiotics
- medical implant biofouling
- industrial biofouling
What is swarming and its advantages?
movement of metabolically active bacteria on v thin layer of liquid on solid surface by secretion of surfacants that decrease surface tension
- colonise niches faster
- less room for tumbles
- better survival
- nutrients shared within group better
What role do magnetosomes play in bacteria?
cell motility directed by Earth’s magnetic field
doesn’t give power or speed but direction which is equally as important
generally gram negative
How are magnetosomes formed?
- Cytoplasmic membrane invagination
- protein sorting
- chain formation and assembly to actin-like magnetosome filaments
- iron transport
- biomineralisation/nucleation
- control of the size and shape of the crystal
What enzymes can be found in carboxysomes?
CA = carbonic anhydrase
transforms HCO3 int CO2 (bicarbonate ion into carbon dioxide)
RubisCO
uses D-RuBP to make 3-PGA which fixes CO2 into a sugar
What are some properties of carboxysomes?
- membrane is impermeable to CO2
- optimises action of rubisco by concentrating CO2 and decreasing quantity of O2 around the enzyme
What are some properties of filamentous cyanobacteria?
- multicellular
- form chains of cells
- gram negative type of envelope
- exchange between cells due to continuous periplasm and septal junctions (small pores/channels between cells)
What are heterocysts?
- differentiated cells that are sensitive to O2
- made by filamentous bacteria under nitrogen deprivation
- specialised in the fixation of atmospheric N2
What are some properties of heterocyst structure?
- number of microcompartments are lost
- additional cell envelope which makes the cell less permeable to gas (except N2)
- necks form at pol in contact w vegetative cells (narrow cytoplasm and septum) and additional cell envelope is thicker = resevoir of organic nitrogen
honeycomb form near poles in contact w vegetative cells = system of contorted intracellular membranes = roles in respiration or photosynthesis
What two main reactions occur in heterocysts?
nitrogenase
N2 into NH4 (nitrogen into ammonium)
glutamine synthetase
NH4 + glutamate = glutamine
What are the 3 locations in which endospores exist in a bacteria?
- terminal spores (at the end)
- subterminal spores (nearly at the end)
- central spores (central spores)
When does sporulation occur (B. subtilis)?
a last resort
it is v complex, energy expensive, and irreversible
occurs when there is a lack of nutrients and high cell density)
only occurs in a subpopulation (~20% of total population)
What are some features of bacterial spores (B. subtilis)?
resistant to heat, desiccation, treatment w detergents, pH and mechanical disruption
has 5 layers: inner membrane, cortex, outer membrane, inner coat, and an outer coat
What is the process of DNA translocation during forespore formation in B. subtilis
- there must be 2 full chromosomes for sporulation to start
- chromosomes condense and origins are tethered at opposite poles
- the septum is formed and 30% of the DNA is already in the forespore
- active translocation of the rest of the chromosome in the forespore by a DNA transporter membrane protein complex
Why is Streptomyces coelicolor a significant bacteria?
it produces more than half of all known antibiotics, metabolites and other bioactive natural products
produced when under stress to destroy competition
How is the spore released from the bacterial cell after formation?
mother cell lysis
What is the definition of a forespore?
a spore that is formed within a bacterial cell
other spores are formed when the mother cell itself differentiates into a spore
How does Streptomyces coelicolor grow on solid medium?
cells branch when growing
growth only found at apical tips
When and how does Streptomyces coelicolor form spores?
when growth becomes limited on solid medium, formation of white, hydrophobic, aerial mycelium occurs (not branched)
not endospores as mother cell differentiates itself into spores
an aerial tip can contain more than 50 copies of the genome
multiple cell divisions occur that creates a chain of spores (unigenomic compartments) that become gray and are released as a result of cell wall hydrolases
What is an important step in Streptomyces coelicolor sporulation in the context of peptidoglycan synthesis?
a switch in peptidoglycan machinery:
vegetative cell = peptidoglycan synthesis at tips of branches
sporulation = peptidoglycan synthesis at the septum to form cell wall
What is a bacterial fruiting body?
during stressful conditions, bacterial cells aggregate to form a complex multicellular structure
typically consists of a stalk and a head
has several benefits such as; allowing bacteria to survive adverse conditions, increasing their dispersal potential, and promoting genetic diversity through horizontal gene transfer.
a large fraction of cells in the fruiting body undergo programmed cell lysis, thought to provide nutrients
the full cell differentiates w 2 entire genomic copies per spore (no endospore)
cells outside the fruiting body are peripheral rods
How do bacterial cells recognise kin?
cells in a fruiting body have high genetic similarity
kin recognition is carried out by a cell surface receptor which are v specific
when kin is recognised they fuse outer membrane and exchange part of their membrane, periplasm and associated proteins
