● Introduction
The production of bacterial cellulose (BC) in Gluconacetobacter hansenii is regulated by the second messenger c-di-GMP. BphS is a photo-activated diguanylate cyclase (DGC) that regulates the synthesis of of c-di-GMP. Upon illumination with near-infrared light, BphS will be activated with changed protein conformation and start to synthesize c-di-GMP. FcsR is a c-di-GMP phosphodiesterase that regulates the hydrolysis of c-di-GMP. When the synthesis rate of c-di-GMP within the cell is higher than its hydrolysis rate, the concentration of c-di-GMP will increase. And the bacteria will produce BC film accordingly. To describe such a process precisely as well as accelerate the engineering cycle, we use modeling to simulate c-di-GMP signaling.
Figure 1. Gene circuit of J23100-B0034-bphS-bphO-J23109-B0034-fcsR- pSEVA331 (BBa_K3740030)
● Modeling
2.1 Reaction Equations:
Photon activation of Bphs

c-di-GMP signaling

2.2 Mathematical Model:
● Results
Figure 2. NIR Lighting Power Density Profile
Figure 3. C-di-GMP Concentration Profile upon NIR Light Illumination
According to the modeling results, near-infrared light has a significant impact on the synthesis of c-di-GMP. The concentration of c-di-GMP is almost zero without light irradiation. However, the concentration of c-di-GMP increases rapidly upon NIR light illumination. Thus, from a theoretical point of view, we can use NIR light to regulate the c-di-GMP concentration.
Figure 4. Comparision of the dry weight of BC film under NIR light and in the dark produced by the engineered bacteria J23100-B0034-bphS-bphO-J23109-B0034-fcsR-pSEVA331-G. hansenii ATCC 53582
The validation experiments results show that light significantly enhances the production of BC films, and that the production of BC film is relatively low in the dark. Although this does not reach an ideal state where no BC film is produced at all in the dark, it still achieves partial light control of BC film production, which is consistent with the trends of modeling results.
● References
[1] Ryu M H , Gomelsky M . Near-infrared Light Responsive Synthetic c-di-GMP Module for Optogenetic Applications [J]. Acs Synthetic Biology, 2014, 3(11): 802.