And the iGEM winner is...

The envelope please: This year's iGEM winner is linkurl:Peking University.;http://parts.mit.edu/igem07/index.php/Peking The team's concept was to create division of labor among bacteria. A group of bacteria can respond to stimuli by adapting to different conditions. But what if the group could split into two, with each population able to behave differently in the same environment? So the team engineered two different systems, which controlled the spatial and temporal dimensions of differentiati

Alla Katsnelson
Nov 3, 2007
The envelope please: This year's iGEM winner is linkurl:Peking University.;http://parts.mit.edu/igem07/index.php/Peking The team's concept was to create division of labor among bacteria. A group of bacteria can respond to stimuli by adapting to different conditions. But what if the group could split into two, with each population able to behave differently in the same environment? So the team engineered two different systems, which controlled the spatial and temporal dimensions of differentiation. The spatial system, which they called Hop Count, uses bacterial conjugation (the transfer of DNA between bacterial cells) to transmit information between cells. They engineered a tandem series of genes that would be passed on through conjugation, with one tandem section being lost at each conjugation. In this way, the cells can count off in an assembly line fashion. "The first cell tells the second cell that it's number 1," Yifan Yang, the group leader explained, then the second cell...
te division of labor among bacteria. A group of bacteria can respond to stimuli by adapting to different conditions. But what if the group could split into two, with each population able to behave differently in the same environment? So the team engineered two different systems, which controlled the spatial and temporal dimensions of differentiation. The spatial system, which they called Hop Count, uses bacterial conjugation (the transfer of DNA between bacterial cells) to transmit information between cells. They engineered a tandem series of genes that would be passed on through conjugation, with one tandem section being lost at each conjugation. In this way, the cells can count off in an assembly line fashion. "The first cell tells the second cell that it's number 1," Yifan Yang, the group leader explained, then the second cell tells the third it's number 2, and so on. The group simply had the tandem series induce green fluorescent protein and red fluorescent protein expression, but presumably, the system could activate expression of biologically useful proteins. The temporal system is called the Push-on-push-off Switch. It is designed to enable cells to switch back and forth between different responses to an identical stimulus. Such a stimulus in nature might be an environmental toxin, or a drop in oxygen levels, but the group used UV irradiation. The cells simply oscillate between expressing green fluorescent protein and expressing red fluorescent protein, but the idea is that a biologically significant response could be used instead. The system is essentially a toggle switch, but with a twist. Consider a light switch -- up is on, and down is off. In this switch, the signal is the same for both conditions. That means that the system must not only respond to the UV signal, but it must also know which response it's currently expressing. It was the group's first year at iGEM, and the 18 members brainstormed for about three months before deciding which idea to pursue, first toying with options such as harnessing bacterial evolution to develop new drugs and creating bacterial "postmen," which could shuttle molecules between different cells. One of the judges, Tom Richard of Penn State, said the Peking group's project was extremely successful in integrating the modeling with the biology and chemistry. And the team also contributed a slew of well-made components to the Registry of Standard Biological Parts (67 so far, with 22 more to come). "They also made a really nice device," Richard said, adding that such a counting system had eluded past efforts and that has "an incredible number of applications." One of the applications, Yang said, might be the biological production of hydrogen. That process has to occur in the absence of oxygen, he explained, but without oxygen, most bacteria can't live. So dividing the labor would allow the bugs to differentiate into two groups -- one that produces hydrogen in the absence of oxygen, and a neighboring aerobic group to fuel the effort.

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