Endospore production by Bacillus subtilis The Bacterial Endospore Differences between
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Microm 410 Fall 2009: Endospores & heterocysts Dr. Parsek Sporulation: Heterocyst formation: filamentous cyanobacteria (Anabaena) Microbial Diversity Bacillus and Clostridium Many bacterial species have the capacity to differentiate: in other words- produce subpopulations with different shapes and/or function Endospore production by Bacillus subtilis • Endospores – Highly differentiated cells resistant to heat, harsh chemicals, and radiation – “Dormant” stage of bacterial life cycle – Ideal for dispersal via wind, water, or animal gut – Only present in some gram-positive bacteria Represents a survival mechanism The Bacterial Endospore Figure 4.38 Spore formers can be classified by where in the vegetative cell the spore forms Differences between Endospores and Vegetative Cells
Transcript of Endospore production by Bacillus subtilis The Bacterial Endospore Differences between
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
Sporulation:
Heterocyst formation: filamentous cyanobacteria(Anabaena)
Microbial Diversity
Bacillus and Clostridium
Many bacterial species have the capacity todifferentiate: in other words- producesubpopulations with different shapes and/orfunction
Endospore production byBacillus subtilis
• Endospores– Highly differentiated cells resistant to heat, harsh
chemicals, and radiation
– “Dormant” stage of bacterial life cycle
– Ideal for dispersal via wind, water, or animal gut
– Only present in some gram-positive bacteria
Represents a survival mechanism
The Bacterial Endospore
Figure 4.38
Spore formers can be classified by where in the vegetative cell the spore forms
Differences between Endosporesand Vegetative Cells
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
Differences between Endosporesand Vegetative Cells
One of the reasons Bacillus anthracis is a good potential biowarfare agent
The Life Cycle of an Endospore-Forming Bacterium
Figure 4.39
“mother cell”
“fore spore”
cell lysis
Endospore Structure
– Structurally complex
– Contains dipicolinic acid
– Enriched in Ca2+
– Core contains small-acid soluble proteins (SASP)
Figure 4.41
Not all spore formers produce oneComposed mainly of proteins and glycoproteins
Hydrophobic: protection adherence pathogenesis
Consists of highly cross-linked proteins (kratin-like)70 different proteins make up 30% total spore protein
Synthesized by mother cell- doesn’t require active protein synthesis when assembled.Primary role is protection from chemical, predators
Region of loosely cross-linked peptidoglycanHelps maintain dehydration of core region
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
Dipicolinic Acid (DPA)
Small Acid Soluble Proteins (SASPs)
Fig. 4.49
10-15% dry weight of a endospore
Bind to DNA and protect molecule, and provide acarbon and energy source for germination
Core also has DNA repair enzymes
Stages in B. subtilis endospore formation
Figure 4.43
Takes about 8h to occur
Vegatative cell
DNA condenses into the axial filament
Beginning of asymmetric cell division
Figure 4.43
Several things happening -engulfment of forespore -synthesis of cortex region -exosporium synthesis
The point of no return
Stage 4 involves synthesis of the coat layer that surrounds the endospore
Culture starts to get resistant to stressa)Continued synthesis of cortexb)Accumulation of DPA/Cac)Production of SASPs
What these stages look like under the electron micrograph
VC
II
III
V
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
Sporulation in B. subtilis is a cascade of gene expression
events in both the mother cell and the developing spore
Lets talk about the regulation of sporulation …
What controls initiation of Sporulation?
P
P
Onset is brought about by starvation (C,P,N)Important that cell density is high
Elaborate decision making process
RNA polymerase: enzyme involved in transcription
‘β
β
2 α
core
holoenzyme
σsigma
Different σ’s direct core RNA pol to bind to adifferent set of genes
A cascade of sigma factors are important during spore formation
Spore formation involves signaling between the fore spore and mother cell compartments.
ProteaseSpoIIAA
SpoIIE
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
Heterocyst Formation
Only certain prokaryotes have the ability tocarryout nitrogen fixation
Two groupsFree-living nitrogen fixersSymbiotic nitrogen fixers
N2 -------> NH3 (NH4+)
organic nitrogen
NO3-
Nitrate (NO3-) Metabolism
NO3-
NO2-
(nitrite)NH3
Dissimilative reduction toammonia; some bacteria
NO (nitric oxide)
N2O (nitrous oxide)
N2
[NH2OH]
NH3 (ammonia)
R-NH2 (organic N)
Assimilative Pathway(plants, fungi,bacteria)
Dissimilative pathway(bacteria only)
NH3-repressed Anoxia-derepressed
Nitrate reductase
Nitrite reductase
Assimilation of Inorganic Nitrogen
Two Mechanisms:1. Glutamic dehydrogenase
α-ketoglutarate + NH3 -----> glutamic acid
2. Second mechanism uses a 2 enzyme system: L-glutamine synthetase and glutamate synthetase orGOGAT enzyme.
Glutamic acid + NH3 + ATP -------> glutamine
Glutamine + α-ketoglutarate --------> 2 glutamic acids
GS
GOGAT
Transamination Reactions
Glutamic acid + OAA Aspartic acid + α-ketogluterate
Glutamic acid + pyruvate Alanine + α-ketogluterate
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
Nitrogenase Complex
-Dinitrogenase reductase-Dinitrogenase
Nitrogen Fixation
Nitrogenase sensitiveto oxygen
Heterocyst formationNitrogen fixation
spaced every 10-20 cellsAnabaena heterocyst
When fixed N becomes limiting …
Microm 410 Fall 2009: Endospores & heterocystsDr. Parsek
glycolipids
Fig. 12.80
O2
Fig. 17.19
Oxygenic Photosynthes
Non-cyclic photophosphorylation
Cyclic photophosphorylation
Fig. 17.22
Calvin-Benson Cycle
phosphoribulokinase
Ribulose bisphosphatecarboxylase (RubisCO)
Heterocysts can not differentiate backinto an oxygenic photosynthetic cell!
Phototrophic heliobacteria: can carry out anoxygenic photosynthesis, sporulate,and fix nitrogen!
Only a few cells undergo differentiation
GOGATglu
microplasmodesmata
