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)
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Microbial consortia are difficult to study All associations are different; Many specific mechanisms (antibiotics, physical barriers etc); No reliable “observables”;
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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)
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…