Transcript The Diel Rhythm that underlies the symbiotic relationship between

Mckayla Burns
Samantha Jackson
Key Words
 Diel- A 24 hour period
 Cytoskeleton- A structural support system made of
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microtubules and microfilaments
Microarray-A technique used for biochemical, genetic
analysis
Chitin-a nitrogen-containing polysaccharide
G3P-is a chemical compound used for the anaerobic
respiration of glycerol
Blebbing- a blistering or swelling that occurs in the
cytoskeleton
About the Authors
Andrew M. Wier
• Associate professor at Pace University
• Uses Euprymna scolopes and Vibrio fischeri as a general model to study
the effects of beneficial bacteria on animal host tissues.
Spencer V. Nyholm
• Previous research: Dominance of Vibrio fischeri in secreted mucus
outside the light organ of Euprymna scolopes: the first site of symbiont
specificity. Appl. Environ. Microbiol., 69(7), 3932-3937.
• Professor at the University of Connecticut
• Also studies the symbiosis between tubeworm and sulfur oxidizing
bacteria in hydrothermal vents
Background Information
Horizontal Transmission:
• Every generation of Euprymna scolopes and Vibrio
fischeri must establish the symbiosis, which is
different from vertical transmission where the
symbiosis is passed from parent to offspring
Mutualistic Relationship:
• The squid provides nutrients for the bacteria and the
bacteria provides the squid with bioluminescence
which is used for the squid’s protection
Background Information
A: Shows the position of the light
organ within the squid, the expulsion
of bacteria from the light organ, and
crypt where bacteria symbionts
resides
B: The blue line symbolizes the
population of the bacteria
throughout a 24 hour period.
Bacteria’s populations are the highest
when the nocturnal host is the most
active.
Figure 1: The diel cycle of the
squid/Vibrio symbiosis
- During expulsion the squid releases
95% of it’s bacteria symbionts,
keeping only 5% to regenerate
General Gene Expression
 The greatest changes in gene expression of the host
cells and symbiont cells occurred before and after
dawn
 The highest up regulation of host genes occurred
before dawn
 The highest percentage of up regulated genes in the
symbionts occurred after dawn
 During some intervals both partners changed the
expression of genes specifically used for signaling and
metabolism
Purpose
 To describe the
transcriptional,
metabolic, and
physiological aspects
of the symbiosis
between Euprymna
scolopes and Vibrio
fischeri and determine
if they follow a diel
pattern
Physiological
Methods:
• Used TEM (Transmission Electron Microscopy)
• Examined the epithelium cells within the light organ of Euprymna
scolopes over 4 different time periods within 24 hours
Results:
• Major change in the morphology of the epithelial cells
• Directly after dawn, the epithelial cells of the light organ are obliterated
• Following this there was an increase in the number of host vesicles
anticipating the creation of new bacterial symbionts
• A few hours later the microvillar border is restored within the epithelial
cells
• Next, the light organ is colonized by new bacteria cells and it is ready
for night fall and bioluminescence
How do the Bacteria Repopulate
the light organ?
 Metabolize the lipid vesicles the host cells creates after dawn
 Host changes its tissue organization in order to provide the
symbiont with glycerol and fatty acids
 Bacteria incorporate fatty acids from host lipids into its
membrane
Fatty Acid Composition of Bacterial Symbionts
 Regulation of
cytoskeleton
genes
 Up regulated
just before dawn
 Down regulated
just after down
 TEMS of the
host crypt
epithelia
Transcriptional Analysis Reveals
Patterns in Symbiont Metabolism
Methods:
 Examined changes in bacterial gene expression during the
day and night
 Microarray analysis of the RNA in the central cores of the
E. scolopes light organs
Results:
 Diel Pattern of Symbiont Metabolism
 Just before expulsion there is an increase in the expression
of genes for the fermentation for chitin
 Just after dawn there is an increase in the expression of
genes for the anaerobic respiration of glycerol
Why do the symbionts shift their
metabolism?
 At night during bioluminescence symbionts use chitin
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fermentation to generate ATP
After dawn and throughout the day the symbionts use
anaerobic respiration of glycerol to generate ATP
The form of anaerobic metabolism may be dependent
on the substrates available at the time
When chitin is available 12% more energy is produced
using fermentation
When glycerol is available more energy is produced
using anaerobic respiration
Evidence of a diel pattern of symbiont metabolism.
Wier A M et al. PNAS 2010;107:2259-2264
©2010 by National Academy of Sciences
Conclusions:
 There is a transformation of host tissue anatomy
 There is a change in gene expression by both
partners
 These changes are controlled by a daily rhythm
 Bioluminescence is maintained by daily
interactions between the squid and the bacteria
Strengths/Weaknesses
Strengths:
• Results for anatomical changes are consistent with diel
rhythm hypothesis
• Results support metabolic changes occur on a diel
rhythm
Weaknesses:
• The source of the nitrate for anaerobic respiration is
still unknown
Further Study:
1. “Although the nutritional conditions within the light organ remain
unknown, taken together, these calculations support the possibility that
over the course of a 24 hour period, the host provides different substrates
to its symbionts to optimize their performance under changing
physiological conditions present in its tissue over the day-night cycle.”
^(Page 2262)
2. Do changes in the anatomy and gene expression present in other
mammalian systems follow a diel rhythm?
 Tissues in Mouse Colon are believed to follow a circadian rhythm
3. Parallels between beneficial and pathogenic bacteria induced
effacement
References:
-http://www.pnas.org/content/107/5/2259.figures-only
-Wier, Andrew M., and Spencer V. Nyholm.
"Transcriptiona Patterns in Both Host and Bacterium
Underlie a Daily Rhythm of Anatomical and Metabolic
Change in a Beneficial Symbiosis." PNAS 107.5 (2010):
2259-264. Print.