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Project Description
I was born in Qingdao, a coastal city known for its mountains, sea, and clear blue skies. In my childhood memories, the seawater was crystal clear, sunlight sparkled on the sand, and the tidal zone was scattered with colorful shells and small crabs.
However, since 2008, things have quietly begun to change. Every summer, vast expanses of green algae would appear along the coastline, covering the sea surface like a blanket. These green patches are known as Ulva prolifera, the primary culprit behind the recurring “green tides” that now occur in Qingdao each year from July to August.
The once-crowded First Bathing Beach became covered in green sludge, emitting a pungent odor. As a child, I didn't understand where it came from. Today, I want to be part of the solution.
Figure: Top view of Qingdao Bay
Ulva prolifera is a species of large green macroalgae belonging to the family Ulvaceae. It is commonly found in temperate and subtropical shallow coastal waters and possesses the following biological characteristics:
Under natural conditions, Ulva prolifera is a normal part of the coastal ecosystem. However, its unchecked expansion—driven by anthropogenic nutrient enrichment and environmental changes—can turn it into a large-scale ecological disaster.
Figure: Ulva prolifera accumulates on the beach.
Through field investigations, literature analysis, and expert interviews conducted by our Human Practices team, we identified two key reasons for the recurrence of green tides in Qingdao:
Source: The seaweed farming rafts in northern Jiangsu
In spring, large quantities of Ulva prolifera spores remain in the shallow sea areas of northern Jiangsu. These spores require a solid substrate for early-stage development, and the structures of Porphyra aquaculture rafts provide ideal surfaces for attachment.
Under eutrophic conditions, these spores rapidly proliferate into filamentous thalli. Once the biomass reaches a critical level, their buoyant structure enables them to float to the surface and continue expanding through photosynthesis.
Ultimately, dense mats of floating Ulva form in the southern Yellow Sea and are carried northward by prevailing winds and currents, accumulating along the coasts of Qingdao and Jiaozhou Bay.
Seasonal factors: July-August is the “outbreak window”
Several environmental factors converge during this period:
Hence, Qingdao is not the origin of the bloom, but rather a convergent zone, where oceanographic conditions result in the accumulation and visible outbreak of green tides.
Massive proliferation of macroalgae can have serious negative effects on coastal environments and human society. In the Yellow Sea, large-scale green tides caused by Ulva prolifera have occurred annually off the coasts of Jiangsu and Shandong provinces for 18 consecutive years (2007-2025). These blooms typically originate as small floating patches in the coastal waters of Jiangsu between mid-April and early May. Driven by monsoon winds and ocean currents, they gradually drift northward along the southern Yellow Sea, accumulating near the Shandong Peninsula during June and July before slowly dissipating.[4]
A notable example is the 2008 outbreak, which coincided with the Olympic Sailing Regatta in Qingdao. The massive arrival of floating algae created severe logistical and environmental challenges for the host city. Direct economic losses from the bloom were estimated to exceed 1.3 billion RMB.
Figure: Figure: The detailed cost of Qingdao government.
I. Physical Control
Figure: Excavator clears Ulva prolifera
II. Chemical Control
III. Biological Control
Figure: Excavator clears Ulva prolifera
To date, no single method provides a fully effective, low-cost, environmentally safe, and scalable solution. Experts emphasize the importance of early-stage intervention and advocate for the integration of multiple complementary strategies to achieve sustainable and comprehensive control of Ulva prolifera green tides.[5]
To handle these problems, we design a programmable salt-tolerant Escherichia coli(E.coli) biofilm with enhanced biofilm adhesion part and arginine short peptide sedimentation part, to curb the spread of green tide from the source by capturing spores. To ensure biological safety, we have introduced a light controlled suicide system and developed a specialized spore filter based on 3D printing to achieve efficient capture and create a green and safe solution.
To address the challenges mentioned above, O! Super Carpet presents a promising strategy involving four interdependent modules: Survival, Light Suicide, Biofilm Enhancement, and Arginine-Inducible Sedimentation Module.
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The high-salinity in seawater can cause dehydration and osmotic pressure imbalance of E.coli cells, disrupting their cell membrane structure and physiological metabolism, making it difficult for them to survive.
In the Survival module, we introduced the salt-tolerant genes, gspM and echM to arm our biofilm with the necessary adaptability against inhospitable conditions. They make it easy for E.coli to maintain normal physiological activities under high-salinity condition (750mM NaCl), which is more harder than the normal sea salinity (600mM NaCl).
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Considering biosafety, we have constructed a blue light-inducible suicide system. With the help of LOVdeg fused with tetR repressor, the engineered E.coli could perceive light with a wavelength of 450-490 nm and regulates the activation of the downstream of tet operon suicide mechanism. As a result, once the engineered bacteria enter the open sea and perceive blue light, they will automatically initiate the suicide program, reducing the risk of horizontal gene transfer.
In spired by that, we designed a blue light-inducible genetic self-destruction circuit to prevent the spread of engineered bacteria in the marine environment:
No light: When light (about 465 nm light irradiation) is absent, the tetR repressor binds tightly to the operator preventing transcription by RNA polymerase.
With light: When cells are under about 465 nm light irradiation, the LOVdeg tag promotes the degradation of the tetR repressor protein. This allows transcription by RNA polymerase.
This initiates the downstream expression of the mazF toxin gene, triggering programmed cell death.
To achieve functional collaboration, we firstly introduced outer membrane-anchored nanobody-antigen(Nb-Ag) pairs into E. coli. Not only does it promote spontaneous adhesion, but it also enables the creation of programmable assembly patterns within the living biofilm.
The Ag-Nb system, a synthetic bacterial cell-cell adhesion toolbox, enables controlled multicellular self-assembly via specific nanobody-antigen interactions. It regulates adhesion specificity and mediates diverse morphologies and patterns compatible with cell growth.
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We have also designed a model to assist researchers in selecting biofilm structures to evaluate the performance of different biofilm structures.
On the one hand, the biofilm formed should be stable and strong enough to capture spores.
On the other hand, we need to grant our biofilm robust adhesion to the hardware and survival capabilities.
In this module, we repair the bcsQ gene in E.coli, in the EPS biosynthesis pathway to increase production. Ultimately, this enhancement contributed to an improved ability to adhere to the hardware and spore capturing.
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Beyond the passive adhesion of Ulva spores relying on hardware operational modes and the intrinsic physicochemical properties of biofilms, a more effective approach is required to promote the spontaneous settlement of spores onto our biofilms. This necessity arises because actively settling spores release the contents of their adhesive vesicles, enabling them to anchor more firmly to the biofilm matrix.
It has been observed that arginine-containing oligopeptides exhibit strong interactions with Ulva spores, inducing multiple forms of spore settlement. Inspired by this finding, we aim to fuse such small-molecule oligopeptides with the common E.coli extracellular platform CsgA. This strategic fusion is intended to endow the biofilm with the capability to actively induce spore settlement, thereby enhancing the efficiency and stability of spore adhesion through a biologically mediated mechanism.
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[1] Kang, P.J. and Nam, K.W. (2016). Effects of temperature and irradiance on growth of Ulva prolifera (Chlorophyta). Korean Journal of Fisheries and Aquatic Sciences, 49(6), pp.845-848. https://doi.org/10.5657/KFAS.2016.0845↩︎
[2] Zhang, Y. et al. (2019). Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China. National Science Review, 6(4), pp.825-838. https://doi.org/10.1093/nsr/nwz026↩︎
[3] Zhao, X. et al. (2019). Cooperation between photosynthetic and antioxidant systems: an important factor in the adaptation of Ulva prolifera to abiotic factors on the sea surface. Frontiers in Plant Science, 10, Article 648. https://doi.org/10.3389/fpls.2019.00648↩︎
[4] Zhang, X. et al. (2022). A review of physical, chemical, and biological green tide prevention methods in the Southern Yellow Sea. Marine Pollution Bulletin, 180, p.113772. https://doi.org/10.1016/j.marpolbul.2022.113772↩︎
[5] Yuan, Z. et al. (2019). Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China. National Science Review, 6(4), pp.825-838. https://doi.org/10.1093/nsr/nwz026↩︎
