microbial consortia are difficult to study all associations are different; many specific mechanisms...
TRANSCRIPT
Microbial consortia are difficult to study
• All associations are different;• Many specific mechanisms (antibiotics,
physical barriers etc);• No reliable “observables”;
• Generic (simplified) models:
1) synthetic communities (wet lab)
2) agent-based models (in silico)
Observed growth patterns
No (very slow) growth Swarming (fast, diffusion limited growth)
Constrained growth
Lab experiment
Sensing
Solitary / Planktonicstate (low signal production)
Activated state (production of secreted factors, increased signal production)
Increased metabolism and movement
Swarming, spontaneous community formation
Biological model: Quorum sensing
QUORUM SENSINGTheoretical model
Simplified example
Signal
Signal
Protease
Protease
aa
aa
Cell 1
Cell 2
Food
“Physicochemical” mechanism: production, diffusion, decay
Theoretical model
Regulatory model
[R-S]
Signal S
Signal synthase I Sensor R
Metabolism
Movement
1) Autoinduction, possitive feedback loop
S2) Equilibrium of internal and external signal levels
3) Can be studied with knockout mutants
Theoretical model
Regulatory model: communication and cooperation
[R-S]
Signal S
Signal synthase I Sensor R
Metabolism
Movement
Signal = communication
Sensing = cooperation
Non-communicating mutant
Non-communicating mutant
Theoretical model
Competition of strains: Cooperation or collapse
WT + SN
24 h
WT + SB
0
20
40
60
80
100
120
0 10000 20000 30000 40000 50000
Time
Rel
ativ
e sp
eed
of
po
pu
lati
on
(%
of
WT
ste
ady
stat
e)
Transient phase Steady phase
WT
WT+SN
WT+SB(QS collapse) SN or SB alone
(no movement)
“No swarming”
(NS)
“Swarming” “Collapse”
(C)
Phenotypes:
B
P. aeruginosaB. cepacia
0
20
40
60
80
100
center
popu
lati
on c
ompo
siti
on (
%)
0
20
40
60
80
100
border
popu
lati
on c
ompo
siti
on (
%)
P.aeruginosa + B. cepacia
A BC
1
WT+BC
2 97:3
Cooperation combines the skills of participants
Divided plate experiment: Center: Rim:
PA: + -
BC: - +
Collapse of a dendritic community
Ádám Kerényi
Blue: WT co-operators
Red: non-cooperating cheats
Computatonal model
B) 16 hours after SB injectionA) Before SB injection
= places of SB injection
C) Escaping dendrite magnified
Collapse is local: it protects against bad mutations....
Communication is not global....Iris Bertani
Lab experiment
Globally communicating community
(e.g. well-mixed, liquid media)
Locally communicating microcommunities
(e.g. swarming, growth on surfaces)
Local collapse, local communication
vulnerable stable
Dóra Bihary
Polymicrobial communities are less efficient but more versatile than (some) monocultures…
Summary
• Microbial communities were modeled with engineered bacteria and computer models.
• Non-communicating mutants can be part of the community, non-cooperating mutants cause (local) collapse.
• Microbial communities are stable because:– Cooperation combines the skills of participants.– Deleterious mutants are eliminated by local collapse
• Stability is a general consequence of local communication, it acts in absence of specific mechanisms… Polymicrobial communities are less efficient but more versatile than (some) monocultural communities…