Biology Reference
In-Depth Information
it would drive the scissors population to extinction. The decrease in the scissors population
would benefit the paper population, which would cause extinction of the rock population.
In other words, the rock
scissors interaction acted as a negative feedback.
Although the mutated rock population had a competitive advantage over the wild-type
rock population, when the community was spatially structured and the interaction occurred
locally, the negative feedback was predicted to favor restrained growth.
paper
To test this hypothesis, Nahum et al. propagated the synthetic rock
scissors
community described above as metapopulations using 96-well microplates, where each well
represented a distinct subpopulation. The degree of population structure was manipulated
by having restricted migration, where migration occurred only between adjacent wells
(i.e. a local interaction), or unrestricted migration, where migration occurred between any
wells (i.e. a global interaction). As a control, the authors also propagated the R strain alone.
After 36 rounds of transfer, the R isolates were randomly sampled and competed against a
labeled variant of their common resistant ancestor to measure their relative fitness. All three
strains persisted in the community for the duration of the experiment regardless of their
migration protocol. However, the authors found that the R strain propagated in the
community with restricted migration evolved to show a significantly lower growth rate than
when the R strain was propagated in the community with unrestricted migration, or when
the R strain was propagated alone.
paper
SPATIAL ORGANIZATION IN SYNTHETIC CONSORTIA
While most synthetic consortia have been engineered to exist as well-mixed cultures, where
the division of labor is separated only through the genetic components intrinsic to each
population, several recent publications have demonstrated that the spatial orientation
of each subpopulation can enhance controllability and the ability of the consortium to
complete a novel task. A spatially organized consortium can arise through two fashions;
it can be organized into biofilms or it can be rationally distributed using technology.
Indeed, the spatial organization of microbial consortia in natural settings has long been
perceived to assist in the establishment of a cooperative behavior that benefits both
populations (e.g.
33
).
250
SYNTHETIC BIOFILMS LEAD TO STABLE CONSORTIA BEHAVIOR
OVER A LONG PERIOD OF TIME
Biofilms have been observed to confer unique benefits in natural systems.
34
Biofilms are
more robust against cellular stress, and thus may allow the persistence of novel behaviors
over greater periods of time as compared to their nonbiofilm-forming counterparts.
13
As such, the construction of synthetic multipopulation biofilms is of particular interest. In
2007, Brenner et al. created a synthetic consortium that consisted of two
E. coli
strains
designed to communicate bidirectionally via QS signals.
35
To engineer this system, the
authors used QS systems originally found in
Pseudomonas aeruginosa
. Two circuits (A and B)
were implemented in separate
E. coli
populations. Both circuits synthesize a small QS
molecule; LasI in circuit A synthesizes 3-oxododecanoyl-HSL (3OC12HSL), while RhlI in
circuit B synthesizes butanoyl-HSL (C4HSL). Genes encoding these proteins are under the
control of a promoter that responds to the opposite population
s QS molecule. That is,
expression of LasI, and thus synthesis of 3OC12HSL, is driven by a C4HSL responsive
promoter. Conversely, expression of RhlI, and thus synthesis of C4HSL, is driven by a
3OC12HSL responsive promoter. To allow identification of both populations, the QS
responsive promoters also drive expression of GFP and RFP, in circuit A and B, respectively.
As such, only when the consortium effectively communicates bidirectionally will both
GFP and RFP be expressed.
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