Lecture 2 microbes

prokaryotes features

• different ribosome format to eukaryotes

• no membrane bound organelles

• diverse metabolism

• respiratory chain in plasma membrane

• transport systems in cell membrane

what most common process does prokaryots use to replicate

binary fission

how do we use otpical density to measure cell mass

A spectrophotometer is used to
pass light of a specific
wavelength (~600nm) through
microbial suspension

The higher the cell density, the
more light scattered by
bacterial cells, less light is
transmitted to the detector

how do we use counting cell number to measure cell mass

• Take sample of bacterial culture at each time point
• Make dilution series and plate out on agar plates
• Incubate overnight – single cells will grow to form visible colonies on plate

what is colony morphology

visible appearance of microbial colonies—such as bacteria or fungi—on solid media like agar

what are the 3 factors we look at when describing morphologies

form

elevation

margin

what 3 sources do organisms require

• energy

• electron

  • carbon

how do organisms obtain energy sources

• Phototrophs gain energy from sunlight
• Chemotrophs gain energy from chemicals

how do organisms obtain electron sources

Organotrophs gain electrons from organic
compounds
• Lithotrophs gain electrons from inorganic
compounds

what is the only photosynthetic
prokaryotes that produce O2

cyanobacteria

what bacteria does not produce O2 but use light and organic compounds as their source of electrons and carbon

purple non - sulfur bacteria

what is a niche

set of environmental conditions in
which a species of microbe can replicate

give 6 examples of a niche conditions that determine where a
microbe can live

• Nutrient availability
• Oxygen concentration
• Temperature
• pH
• Solute concentration (osmolarity) &
water activity
• Pressure, Light intensity, Radiation

What adaptations might allow bacteria to grow optimally at very different temperatures?

• membrane fluidity - higher fluidity helps colder temps

  • protein structure and stability

  • mechanisms maintaining DNA and RNA stability

what are 3 other ENVIRONMENTAL FACTORS that helps microbes survive

• solute conc

• pH

  • pressure

how does solute conc effect microbe survival in the environment

• Halophile – require high levels of sodium chloride (>0.2M) for growth
• Osmotolerant – grow over a wide range of water activity
• Xenophile – grow best at low water activity

how does pressure effect microbe survival in the environment

Piezophile (or barophile) – grows optimally at high hydrostatic pressure

what is an extremophile

grow under harsh conditions that would kill most other organisms

what are the 2 different lifestyles microbes have

• freeliving

  • microbe host interactions

what are the 3 types of microbe host interactions and define them

• pathogenic - • Interact with host organism; host
  damaged

• mutalistic - Interact with host organism; both
  partners benefit

  • commensal - Interact with host organism; one partner
    benefits, other unaffected

what is Quorum sensing

gene regulation in response to population density

what are the four types of microbial ineractions and explain

• Mutualism – reciprocal
benefit to both partners,
obligate interaction
• Cooperation - reciprocal
benefit to both partners, not
obligate
• Commensalism - one
organism benefits (the
“commensal”) and the other
is neither harmed nor helped
• Predation – one microbe
feeds on another microbe

• Parasitism – one organism gains
(“parasite” / “pathogen”) and the
other is harmed (“host”)

• Amensalism – negative impact of
one organism on another, based
on release of a specific compound
e.g. antimicrobial, toxin
• Competition - two organisms try
to acquire or use the same resource

what is a biofilm

Community of microbes firmly attached to a surface with the aid of extracellular polymeric substance (EPS) matrix e.g plaque, can be resistant to

what is heterogeneity

differences in metabolic activity and locations of microbes

is there HETEROGENEITY IN BIOFILMS

yes

how does a microbe obtain carbon sources

• Autotrophs use CO2 to make carbon
compounds (primary producers)
• Heterotrophs use organic compounds from
their environment

what is photolithoautotrophs and example

organism that uses light for energy, inorganic molecules e.g cyanobacteria

what is the nucleoid

• location of chromosomes and associated proteins and not membrane bound

  • contains 1 closed circular double helix stranded DNA molecule

what are plasmids

• extrachromosomal DNA found in bacteria, archaea, some fungi

what is the shape of plasmids

circular

plasmid function

carry accessory genes that can give bacteria an advantage under particular environmental conditions

what are the 5 different types of accessory genes and what they do to help bacteria

Conjugative → enable DNA transfer between bacterial cells
• Resistance (R) → provide resistance to antibiotics or other antimicrobials
• Bacteriocin → produce compounds that kill or inhibit competing bacteria
• Virulence → carry genes that enhance colonisation or disease
• Metabolic → enable degradation or use of unusual compounds

bacteria cell wall function and structure

• rigid structure

• maintains cell shape

• protects cell

what is peptidoglycan

a mesh like polymer found in bacteria cell walls which has cross linked strands for strength

what is the structure of peptidoglycan

• helical structure consisting of two alternating sugars:NAG and NAM

what colour does gram positive bacteria show as under microscope

purple

what colour does gram negative bacteria show as under microscope

pink

what is a gram positive cell wall mainly composed of

peptidoglycan

what makes a gram negative cell wall different to a gram positive cell wall

• GN more complex than GP

  • GN contains only thin layer of peptidoglycan

what is LPS

a characteristic component of the
outer membrane of Gram-negative bacteria

what does LPS consist of

• Lipid A
• Core polysaccharide
• O side chain (O antigen)

what is a capsule

gel like layer, composed of polysaccharides. provides protective advantages e.g. reduces phagocytosis

what are s layers

Regular, self-assembling layers of
protein or glycoprotein on the cell
surface

function of s layers

• protect against harmful environment and substances

  • helps cell structure

flagella functions

• mobility