Bacterial Growth and Physiology

 

 

 

Differential Media Example

MacConkey
Lactose utilization
Bacteria import lactose (a disaccharide); metabolize glucose using fermentation, producing acid
Dye shows change in pH, indicating fermentation of lactose

 

 

 

Liquid Media

Good for growing specific amounts of bacteria and for growing large amounts of bacteria

Types of liquid media (also applies to solid media)

Complex
Defined

 

 

 

 

Media Classifications

Complex : contains uncharacterized mixtures of compounds.
Usually used for routine growth (cheap, easy to make)
Defined : uses specific chemicals
Used for nutritional studies
Requires knowledge (or trial and error) of requirements of bacteria
 

Minimal: only has the minimal components for growth of a particular bacterium

 

 

 

Heterotroph

(short for chemoheterotroph) or ‘Organotroph refer to bacteria that use organic C as both energy and C source
Most pathogenic bacteria fall into this category

 

 

 

Basic Growth Requirements for Bacteria

Inorganic
N, C, O, H
S
P
K, Na (some), Cl (some)
Mg, Ca (some)
Trace elements (Fe, Cu, Zn, Mn, etc.)
Vitamins and growth factors (some bacteria)

 

 

 

Environmental Requirements for Bacteria

Temperature

pH

Oxygen

Salt

 

 

 

Atmospheric Requirements 

Anaerobes
Obligate (i.e. intestinal bacteria)
Aerotolerant– does not use oxygen but tolerates it

Utilize fermentative metabolism or ’anaerobic respiration: use of electron acceptors other than O2
Aerobes
Obligate aerobes
Microaerophiles
Require low oxygen tensions; harmed by oxygen concentrations that are too high.
Both utilize respiratory metabolism (O2)
Facultatives (aerobic or anaerobic)

  Utilize respiratory or fermentative   metabolism (respiratory preferred if   oxygen present) – ex: E. coli

 

Aerotolerant anaerobes

Can grow in the presence of oxygen but do not utilize respiratory metabolism (utilize fermentative metabolism under all conditions.  ex: Streptococcus pyogenes

 

 

 

Generation Time

Generation Time
Cells divide by binary fission at a constant rate
Period between the time that a new cell arises and the time that this cell completes division into two new daughter cells is known as the generation time

 

 

 

Catabolism of Carbohydrates

Glycolysis

Followed by

Fermentation or
Respiration

Goals:  ATP generation

Generation of metabolic building blocks


 

 

 

 

 

Basic Facts of Glycolysis

Substrate level phosphorylation
Not very efficient
Lots of C utilized
Lots of energy remains in the end products
Different bacteria utilize different glycolytic pathways!

 

 

 

Embden-Meyerhof-Parnas  Pathway 


Net ATP yield = 2 moles of ATP per mole of glucose fermented
Not very energy efficient
Lots of energy remaining
Need to further metabolize pyruvate
Fermentation used (see below)

 

 

 

HexoseMonophosphateGlycolytic Pathway 

Provides NADPH and pentoses for biosynthesis
Pathway for utilization of pentoses as C and energy sources
Makes ribose-5-phosphate, key intermediate for production of nucleotides
Also called Pentose phosphate pathway (PPP)

 

 

 

Entner-Doudoroff (ED) glycolytic pathway 

Replaces the EMP pathway in many pseudomonads.
Less energy efficient than EMP pathway (1 ATP/mole glucose).
Usually utilized under aerobic conditions.

 

 

 

Fermentation

Used by anaerobic bacteria or by facultatives under anaerobic conditions
These organic end products are used as electron acceptors to recycle NADH, which is produced during glycolysis, to NAD+
End product depends on bacterial species
Identification of bacteria
Industrial value
Stinks!

 

 

 

Anaerobic respiration 

Electrons transferred from reduced carbon compound (acetate, fumarate) and NADH (which are oxidized to NAD+) through electron carriers similar to aerobic electron transport chain (but distinct carriers) to various electron sinks (which are reduced)
ATP generated in the process, but <38 ATP that is seen in aerobic respiration; yields vary
nSO42-        H2S  Sulfate reductase
nNO3         NO2 Nitrate reductase
nHCO3         CH4 Methyl Co-M reductase

 

 

Energy Yields
Fermentation vs. Respiration 

From Most to Least:

 

Glycolysis+TCAcycle+electron transport
38 ATP/mole glucose
 
-Glycolysis+Anaerobic respiration
Variable ATP yield, but more than fermentation
Glycolysis+fermentation
EMP
2 ATP/mole of glucose
HMP & ED
1 ATP/mole glucose

 

 

 

Anabolic reactions 

-E. coli can synthesize all cellular components from glucose, N, S, P

source, some trace metals, and some salts! 

Related Essay Examples

Add a Comment

Your email address will not be published. Required fields are marked *