Essential nutrients
those that must be supplied from the environment.
Major elements in cell macromolecules
C, O, H, N, P, S
Cations necessary for protein function
- Mg2+, Ca2+, Fe2+, K+
Micronutrients
Trace elements necessary for enzyme function - Co, Cu, Mn, Zn
different ways organisms acquire carbon
autotrophs and heterotrophs
Autotrophs
- fix CO2 and assemble into organic molecules (mainly sugars).
- include: Photoautotrophs, and Chemolithautotrophs
Heterotrophs
- use preformed organic molecules
- Photoheterotrophs and organotrophs
phototrophs
obtain energy from chemical reactions triggered by light.
Lithotrophs
-use inorganic molecules as a source of electrons.
chemotrophs
obtain energy from oxidation-reduction reactions.
organotrophs
-use organic molecules
proton motive force.
electrochemical potential formed from H+ gradient and the charge difference
N2 makes up ___% of Earth's atmosphere but is unavailable for use by most organisms.
79%
Nitrogen fixers
possess nitrogenase, which converts N2 to ammonium ions (NH4+).
Nitrifiers
oxidize ammonia to nitrate (NO3-).
Dentrifiers
Convert nitrate to N2
3 ways to achieve selective permeability
1. Permeases - substrate-specific carrier proteins
2. Dedicated nutrient-binding proteins
3. Membrane-spanning protein channels or pores.
Facilitated diffusion
- helps solutes move across a membrane from a region of high concentration to one of lower concentration.
- no energy needed
THREE MAIN TYPES OF ACTIVE TRANSPORT
1) Coupled transport systems
2) ABC transporters.
3) Group translocation
Coupled transport systems
- energy released by moving a driving ion down its gradient is used to move a solute up its gradient.
- Symport and anitport
symport
the two molecules travel in the same direction.
antiport
the actively transported molecule moves in the direction opposite to the driving ion.
ABC transporters.
-Powered by ATP
- Found in all 3 domains of life
-2 main types Uptake and Efflux
Uptake ABC transporters
critical for transporting nutrients.
Efflux ABC transporters
used as multidrug efflux pumps.
Siderophores
specialized molecules secreted to bind Fe3+ and transport into the cell
Group translocation
-A process that uses energy to chemically alter the substrate during its transport.
- ex: phosphotransferase system (PTS)
We have succeeded in culturing only ____% of the microorganisms around us.
0.1%
Bacteria are grown in culture media, which are of two main types:
1. Liquid or broth
2. solid (usually gelled with agar)
Liquid or broth
Useful for studying the growth characteristics of a pure culture
Solid
Useful for trying to separate mixed cultures from clinical specimens or natural environments
Pure colonies are isolated via two main techniques
Dilution streaking and spread plate
Dilution streaking
-Easier than a spread plate
-Dragging a loop across the surface of an agar plate
Spread plate
-Tenfold serial dilutions are performed on a liquid culture
-A small amount of each dilution is then plated
Complex media
nutrient rich but poorly defined.
Minimal defined media
contains only those nutrients that are essential for growth of a given microbe
Enriched media
complex media is supplemented with what the organism needs (such as blood or serum)
Selective media
growth of one organism over another.
example - NaCl filled media
Differential media
Differential media exploit differences between two species that grow equally well.
Growth factors
- specific nutrients not required by other species
- microbe need them in order to be able to grow in laboratory media.
Obligate intracellular bacteria
- unculturable
Petroff-Hausser counting chamber
Microorganisms can be counted directly by placing dilutions on a special microscope slide
-uses a grid for a quick counting method
How to distinguished dead cell
- by fluorescence dye
- dead cell appear orange or yellow due to propidium
- live cells appear green because of Syto-9
Fluorescence-Activated Cell Sorter (FACS) - or flow cytometer
- "Fluorescent" cells are passed through a small orifice and then past a laser.
- Detectors measure light scatter in the forward direction and to the side
Viable bacterium
being capable of replicating and forming a colony on a solid medium.
Microorganisms can be counted indirectly via
- biochemical assays of cell mass, protein content, or metabolic rate
- and by measuring optical density
Growth rate
- rate of increase in cell numbers or biomass, is proportional to the population size at a given time.
- exponential curve
- never last indefinitely
Generation time
the time it takes for a population to double.
batch culture
a liquid medium within a closed system used for culture bacteria
way to model the effects of a changing environment
4 stages of bacterial growth
Lag phase- In shock, making proteins to start using food.
Log phase - when they really start reproducing
Stationary phase-cells achieve a steady state
Death phase- food is running out, cells are dying
Continuous culture
all cells in a population achieve a steady state, which allows detailed study of bacterial physiology.
chemostat
Type of continuous culture that ensures logarithmic growth by constantly adding and removing equal amounts of culture media.
ex: human gastrointestinal
Biofilms
- bacteria form specialized, surface-attached communities
-1 or multiple species
- form organic or inorganic surfaces
Bacterial biofilms form when
- nutrients are plentiful
- when depleted, individuals detach
- different forms and functions for different species
Quorum sensing
- chemical signals enable bacteria to communicate
- some cases to form biofilms
Biofilm development involves
- the adherence of cells to a substrate
- the formation of microcolonies
- the formation of complex channeled communities that generate new planktonic cells.
Cell differentiation
under stress, cell structure changes
What species can produce dormant spores that are heat resistant.
Clostridium and Bacillus
What initiates an elaborate 8-hour genetic program
Starvation
Forespore
Forms endospores
Sporulation can be divided into discrete stages based on ...?
morphological appearance.
Anabaena differentiates into specialized cells called
Heterocysts
-Allow it to fix nitrogen anaerobically while maintaining oxygenic photosynthesis
Myxococcux Xanthus uses
Gliding motility
As nutrients decline, aerial hyphae divide into
arthrospores that are resistant to dying