microbial nutrition and growth - weber state …faculty.weber.edu/coberg/2054 slides/microbial...

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 1

Microbial Nutrition

n All life requires: ¨ Electron flow, to drive all life processes

n  Drives ions into, out of cells n  Used to create ATP

¨ Energy, to move electrons

¨ Materials, to make cell parts n  Nutrients


Microbial Nutrition

n Electron flow requires:

¨ Source of electrons n  Lithotrophs

¨  Inorganic molecules are electron donors

n  Organotrophs ¨ Organic molecules are electron donors

¨ Ultimate electron acceptor n  Inorganic molecules

¨ Respiration

n  Organic molecules ¨ Fermentation


Microbial Nutrition

n Source of energy

¨ Phototrophs n  Light energy excites electrons n  Excited molecules are electron donors

¨ Chemotrophs n  Chemicals are electron donors n  Oxidation of chemical

¨ Oxidation = donation of electrons ¨ Electron acceptor is reduced


Microbial Nutrition

n Nutrients

¨ Must be supplied from environment ¨ Macronutrients

n  Major elements in cell macromolecules ¨ C, O, H, N, P, S

n  Ions necessary for protein function n  Mg2+, Ca2+, Fe2+, K+

¨ Micronutrients n  Trace elements necessary for enzyme function


Microbial Nutrition

n Different microbes require different

additional nutrients ¨ Amino acids ¨ N from air (N2) vs. from soil, other organisms ¨ Electron acceptors

n  Aerobic (O2) vs. anaerobic organisms

¨ Energy source n  Light vs. organic energy source


Nutrient Uptake

n Passive diffusion ¨ Some gases pass freely through membranes

n  O2, CO2

¨ Follows gradient of material n Facilitated diffusion

¨ Transporters pass material into/out of cell

¨ Follows gradient of material


Nutrient Uptake—Active Transport

n ABC Transporters ¨ Use ATP energy to pass

material into cell ¨ Transport material against

gradient



n Symport and Antiport ¨ Gradient of one molecule transports another

n  Electron transport creates Proton-Motive Force n  PMF transports other molecules

¨ Transports material against its gradient Symport: Gradient of pumps in same direction

Antiport: Gradient of pumps in opposite direction



n Phosphotransferase System (PTS)

¨ Uses ATP energy to pass material into cell

¨ Modifies material as it enters cell n  Gradient is maintained,

pushing material into cell

glucose enters cell and is phosphorylated. As a result, gradient of pushes more glucose inside. (glucose-6-phosphate) cannot pass out of cell.


Animation: Phosphotransferase System (PTS) Transport


Click box to launch animation


Culturing Bacteria

n Culture media has all materials necessary for growth ¨ Varies for different bacterial species ¨ Electron source ¨ Energy source

n  If not phototrophic

¨ Carbon source n  If not autotrophic

¨ Nitrogen source n  If not N2-fixer


Obtaining Pure Cultures

n Dilution streaking

¨ Streak cells on plate ¨ Agar inhibits spread of

microbes on plate ¨ All cells in colony derive

from single cell n  Genetically identical n  Clone of that original cell


Obtaining Pure Cultures

n Dilution in liquid culture

¨ Reduces number of cells in each tube ¨ Spread liquid on plate to see single colonies


Counting Bacteria

n Petroff-Hauser chamber ¨ Counts cells directly ¨ Gives accurate number ¨ Can’t tell if cells are alive or dead

n  Use stain to distinguish living cells


Counting Bacteria

n Spectrophotometer

¨ Measures optical density n  “Shadow” of bacteria

¨ Gives rapid measurement ¨ Can’t tell if cells are alive or dead ¨ Solution must be at 107–1010 cells/ml

Drawing of light bulb Photodetector


Counting Bacteria

n Viable counts

¨ Counts only cells able to reproduce n  Form colonies

¨ Requires time to form colonies (overnight)


The Growth Cycle

n  Lag phase

¨ Cells synthesizing materials, not dividing n  Log phase = exponential growth

¨ 1 → 2 → 4 → 8 → 16 … n  10 doublings increases density by ~1000 n  log10(N) increases linearly

n Stationary phase ¨ Cells no longer growing

n Death phase


The Growth Cycle

Log scale necessary to show wide range of concentrations


Cell Differentiation

n Cells respond to changing environment

¨ Endospores n  Protect against bad conditions n  Disseminates cells

¨ Forms inside (“endo”) mother cell




¨ Heterocysts n  Different cells produce different

nutrients ¨ Vegetative cells—energy ¨ Heterocysts—fixed nitrogen

¨ Myxospores n  Form inside fruiting body

¨ Multicellular structure




¨ Actinomycetes form spores n  Food runs out n  Produce aerial hyphae n  Protect against bad conditions n  Disseminates cells

Spores


Biofilms

n Cells secrete material to hold to a surface ¨ Cells acting together

n  Multiple species or a single species

¨ Cells signal to each other n  Quorum sensing

¨ Protects against dispersion ¨ Prevents antibiotics

from infiltrating

microbial nutrition and growth - weber state …faculty.weber.edu/coberg/2054 slides/microbial...

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