SCELSE researchers have developed a biofilm-based logic gate that responds to light, paving the way for potential biotech applications in the future.
"This is the first report on engineering a bacterial biofilm to respond to near-infrared (NIR) light," said Asst Prof. Cao Bin from SCELSE and NTU School of Civil and Environmental Engineering (SCEE), who is the senior author of this study.
Logic gates are basic building blocks in digital electronics that can be assembled to perform information processing and complex computation. These gates are usually made using semiconductors which have a very predictable behaviour when a specific input is applied.
In recent years, the microbial fuel cell (MFC) has shown much promise in various applications such as wastewater treatment and self-powered chemical sensors. MFCs have been also been tested in information processing systems, where they are developed to work as logic gates when specific chemical inputs result in an electrical signal output.
However, biofilm-based logic control in MFCs is very challenging because biofilms are highly dynamic.
SCELSE researchers developed a biofilm-based logic control strategy in an MFC by adding an engineered NIR light responsive c-di-GMP module into Shewanella oneidensis MR-1 bacteria. c-di-GMP is an important signalling molecule that coordinates biofilm formation. The module responds to the presence of two inputs: NIR light and a chemical called isopropyl β-D-thiogalactoside (IPTG).
Only when both inputs are present will the module enhance biofilm formation on the anode of the MFC, resulting in a large increase in electrical output. A logic gate that sends an output signal only when both inputs are present (1,1) is called an “AND” gate.
The researchers first tested the logic gate using a static biofilm assay as a proof of principle and found significantly higher biofilm biomass when both inputs are applied, as they expected. They then set up MFCs to test the electrical output of their system, and measured the maximum power density with input of (1,1) to be twice as high compared to other input combinations, which is very robust result.
Since this logic gate is based on c-di-GMP which is a universal biofilm regulator, the same approach can also be applied to other bacterial species. In addition, the use of NIR light instead of purely chemicals as inputs expand the applications in scenarios where less chemical use is required. This gene circuit can potentially be used to construct NIR light-controllable biofilms for applications such as bioremediation and biochemical production.
"Control of biofilm development is critical to achieve a desirable performance of biofilm-mediated bioprocesses. This work suggests that we may use light to 'guide' biofilm development in bioreactors for biotechnological applications," Asst Prof. Cao explained.
His research team is currently applying this approach to control the development and performance of a catalytic biofilm in continuous, flow-through bioreactors.
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