The flagellar motor is reversible
CCW: run
CW: tumble
E. coli responds to chemical gradients by biasing its random walk
No stimulus
Gradient of chemoattractant
[Asp], e.g.
Chemotaxis
- the ability to sense and respond to extracellular
concentration gradients of solutes
Input
Chemoreceptors
CheY – P
- CW signal
- 3 sec. lag
bacterial cell
Output:
motor bias,
CCWCW
rotation
There are likely four different types of
surface motility systems (each may be genetically unique)
1) Twitching
- extension and retraction of a pilus (type IV)
- found in multiple groups of bacteria
2) Cyanobacteria
- polysaccharide extrusion
3) Mycoplasma
- ATP driven system of just two proteins
4) Flavobacteria
- Unknown
What is Known about Flavobacterial Motility
- the cell surface is smooth and featureless by EM
- motility is connected to the ability to utilize the
insoluble polysaccharide chitin
- non-motile cells are resistant to bacteriophage
- a number of the genes essential to motility have
homologs involved in macromolecular transport
Macromolecule Transport Model of F. johnsoniae Gliding
Direction of Cell Movement
OM
PG
CM
ATP?
H+?
H+
Substratum
Summary
There are two classes of bacterial motility
- flagellar (swimming)
- bacterial vs. archaeal flagella
- horizontal gene transfer
- chemotaxis
- surface motility
- twitching (type IV pili)
- polysaccharide secretion
- ATP driven
- Flavobacterial system
- may involve transport
Chapter 5: Nutrition, Cultivation, and Isolation of Microbes
Evolution of Metabolic Diversity
Bacterial Nutrition Types
1-2-1, C-H-O ratio, Most biosynthesis is done using units of
CH2O. So if an organism is using sunlight for energy and CO2 as a
carbon source then it needs a source of H+ (in plants it would be H2O).
Carbon Source: CO2 or other organic carbon
Energy Source: Sunlight or chemical energy
Alternate Terminal Electron Acceptors (other than O2)
CO, NO3, SO4, SO3, oxidized metals
Bacterial Nutrition Types:
Photoautotroph
Carbon source: CO2
Energy source: Sunlight
*Photoheterotroph
Carbon source: Carbon compounds
Energy source: Sunlight
*Chemoautotroph
Carbon source: CO2
Energy source: chemical energy (H2S, H2, metals, etc.)
Chemoheterotroph
Carbon source: Carbon compounds
Energy source: Reduced carbon compounds (CH2O)
Some Terms (as applicable to microbial growth)
Aerobic vs. Anaerobic
Obligate: required for survival
Facultative: optimal for growth but not required for survival
Trace (Micro Nutrient): required in very small amounts
Sole Source: the cited molecule can satisfy an organism’s
needs for a particular nutritional requirement alone,
with no need for additional sources (often seen in
selective growth media)
Enrichment Culture: A technique to encourage the growth of
a specific microbe using metabolic traits particular to
that organism from a starting mixture of many
organisms. (ex. Mycobacterium)
Getting Nutrients into the Cell
--- remember the cytoplasmic membrane is a true permeability
barrier, most nutrients can’t cross on their own
Diffusion: Use existing concentration gradients to move material in or
out of the cell. Usually requires a channel protein (facilitated
diffusion)
Group Transport: A sort of one-way facilitated diffusion, utilizes an
existing concentration gradient to get molecules into the
cell and then chemically modifies the molecule to prevent its
escape back out through the channel protein in the membrane
Active Transport: Use an energy source to offset the “cost” of moving
a molecule against its concentration gradient
Simple Diffusion with Facilitator Protein
Different Types of Transporters
Uptake of Micronutrients
Siderophores: small organic molecules able to bind specific
substrates with very high affinity
--- used to capture low abundance micronutrients from the
cell’s surrounding environment
--- usually coupled with a specific uptake system of
proteins on the cell’s surface
Enterobactin, from E. coli