One of the most interesting and complex types of group behaviors in animals is that in which several organisms simultaneously repeat the same activity at regular intervals of time.1 In ordinary usage, this kind of behavior is called “synchronous”. It has been observed in Thailand that male Pteroptyx malaccae fireflies, congregated in trees, flash in rhythmic synchrony with a period of about 560 ± 6 msec (at 28°C). Males of a China’s special species of firefly called Qiongyuying flash synchronously during mating season. And we also observed that bees crawling in the same small area display a synchrony of wings fluttering in order to scare off intruder，and we filmed a video clip to demonstrate this phenomenon.
Moreover, synchrony has been described in a range of mammal groups, including odontocete cetaceans (a kind of toothed whale).2 The odontocete cetaceans behave synchronously when they breathe on the surface of water.
In the microcosm, a synthetic gene oscillator whose oscillatory cycle can be tuned by altering inducer levels, temperature and the media source has been designed by I and his cooperators to accomplish the synchronous oscillation. It uses both E.coli and yeast as component cells. In this oscillator system, chemicals (IPTG, arabinose) are used as a series of signals to initiate synchronous oscillations within single cells of the colony.3
Compared with chemical molecules, optical signal is more efficient for both the macrocosm and the microcosm. We wonder whether we can change the induced signal into light, which is visible and easy to control. It propagates much faster and has countless channels, for each wavelength is a different channel.
Recently, there has been increased interest in visible light controlled system. Optogenetics, a seven-year-old field branching out from molecular biology and neuroscience, is leading the trend of creating novel synthesized proteins as “tools”
helping people understand the brain mechanism. These “opsins”, which light-activated domain borrowed from microbes or plants, were transferred into model animal organisms. These controllers are acting in the center part of light system. Unlike the drug treatment, light can be delivered by lasers with extremely high spatial precision; therefore, one can manipulate only target cells.
Our Biowave project is more than performing “Optogenetics can solve controversies that have been going on for many, many years.”light control. By establishing the light depending feedback system within the cell we have realized a light communication system. This is the very first time that putting the intracellular and intercellular light communication in the biological system. Using the fundamental gene circuit and brand new parts we created, each cell becomes a communication node.
The first Biowave circuit we have created is the Negative Feedback Biowave. The circuit comprising light sensor and light generator established the negative feedback between them. The properties of time delay, caused by gene expression or the accumulation of the element’s concentration, and negative feedback could form an oscillation of light output within a single cell or the neighbouring cells. By placing the bacteria on a Petri dish and letting them evenly distributed, each cell could sense the light of others equally. With the certain condition and observation analysis, the whole dish could form a detectable synchronized oscillation. In a macroscopic view, this kind of synchronization could be distracted by the attenuation of light. So we could expect a wave like pattern on this level.
The Positive Feedback Biowave is another attempt for the intracellular and intercellular light communication. Thus the positive feedback under this situation makes the system a bistable circuit; each cell can remain in either a light state or a dark state. But the light irradiation across the colony makes things different. The bacteria would form a static strip or other bistable system caused patterns within or beyond our expected.
|
LIGHT |
CHEMICAL |
|
|
|
| manipulate |
controllable |
Hard to control |
|
| elimination |
light induction could be changed
or erased |
hard to wipe out |
|
| transfer
speed |
Signal travels fast(as a speed
of light)
Non-time-delay |
Speed is limited by chemical
diffusion System has a minimum delay |
|
| crosstalk |
never has the crosstalk with
constitutive pathway |
may cross the constitutive
pathway |
|
| measurement |
Visible and detectable
easy to measure |
hard to detect or measure |
|
| noise
immunity |
sensitive
could be easily disturbed by the nature light |
only the same molecule or the
analogue could disturb the signal pathway |
|
|
| channel |
has limited channels(only 390nm
to 700nm) |
countless channels(each kind of
chemical analogues group is a channel) |
|
Establish feedback system
Feedback exists between two parts when each affects the others. In our system, these two parts are the light sensor and the concentration of the light generator protein. By involving the light sensor in the loop, we can establish the feedback.
Light generator
ApproachNext issue we placed our focus on the properties of the candidate parts. At the beginning we laid eyes on the luciferin illumination system. But the engineering bacteria we were using do not have the luciferin producing enzyme system or the luciferin cycle. Fortunately the 2010iGEM Cambridge has successfully deliver this cycling system into the E.coli. But the wave length does
not fit the light sensor which we will discuss later. So we picked another well-known bio illuminator, the Lux operon. It is also presented by 2010 Cambridge.
Lux operon
The Lux operon is a set of genes active in bacterial luminescence. The genes encoding the luciferase and a fatty acid reductase complex which synthesizes the substrate are contained in a single operon. When cloned into a recipient host, the lux operon facilitates the generation of a 
blue-green light with a maximum intensity at 490 nm without the requirement of adding exogenous substrate, which was the prime reason why we chose it to be our light source in this study.
In our project, we using PCR extracted the DNA sequence from the BBa_K325909, and cloned it under the controllable promoter. The coding device relieved from the original promoter is also available as the BBa_K785003. The growth curve of the Lux transformed dH5α strain is measured. See the summery at the result page.
Light sensor
ycgF-ycgE-ycgZ endogenous light sensing system
Light sensor that directly regulates the expression at the transcription level is rarely seen. Bacterial opsins usually appeal as light activated kinases or phosphodiesterases.
BBa_K238013, an exact promoter of the blue light receptor, is a portion of an E.coli constitutive light sensing system. This system consists of a receptor, ycgF, which is responsive to blue light. When blue light strikes, the 
When blue light strikes, the receptor changes conformation and dimerizes driven by the BLUF-domain. This allows it to bind to the ycgE repressor through its EAL-domain, releasing the repressor from the promoter region. In summary, the irradiance of blue light will cause a positive induction, expression downstream
Light sensing feedback using ycgF-YcgE-YcgZ sensing system.
MG1655 strain
The PCR process results that dH5α,the strain we used as normal competent cell, does not contain such endogenous system. The MG1655 strain as a wild type of E.coli K12 was used for the construction of our light sensing design. See MG1655 genotype.
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