Periodic Reporting for period 1 - AlgaeLeaf (Light-responsive microalgal living materials)
Reporting period: 2022-02-01 to 2024-07-31
The aim of the AlgaeLeaf ERC project is to develop microalgae-based photosynthetic living materials. The field of engineered living materials (ELMs) presents lots of potential, and in particular, microalgae-based ELMs are highly promising due to the light-driven response of microalgae. Although this new field presents lots of promise, many fundamental questions remain open before microalgae-based living materials can reach their full potential.
In order to fabricate more complex and/or more efficient light-responsive microalgal living materials, it is important to gain more fundamental knowledge regarding the growth and motion of microalgae within a porous hydrogel. During the first two years of the project, my team has focussed principally on investigating how cells grow within a porous environment and on characterizing the photosynthetic activity of the microalgae when embedded in a porous hydrogel. We have also studied the coordinated beating dynamics of the flagella when swimming.
In order to fabricate more complex and/or more efficient light-responsive microalgal living materials, it is important to gain more fundamental knowledge regarding the growth and motion of microalgae within a porous hydrogel. During the first two years of the project, my team has focussed principally on investigating how cells grow within a porous environment and on characterizing the photosynthetic activity of the microalgae when embedded in a porous hydrogel. We have also studied the coordinated beating dynamics of the flagella when swimming.
We have studied the motility, growth, spatial distribution, and photosynthetic activity of eukaryotic microalga Chlamydomonas reinhardtii in a nanoporous hydrogel matrix. 3D printing has been used to control the shape of the biohybrid living hydrogel material as a whole, while light exposure and access to carbon source has been used to control the growth and location of the cells within the material. A custom-built CO2 measurement chamber has been designed and used to monitor the cells photosynthetic activity. The microalgal cells inside the hydrogel are found to photosynthesize and to form confined cell clusters, which grow faster when located close to the periphery of the hydrogel due to favorable gas exchange and light conditions. We have identified that a higher surface to volume ratio leads to higher photosynthetic activity in living materials. Interestingly, this strategy resembles the established adaptations found in multicellular plant leaves. These results have been published in the journal Advanced Materials in January 2024 (Oh JJ et al. “Growth, Distribution, and Photosynthesis of Chlamydomonas reinhardtii in 3D Hydrogels” Adv. Mater. 2305505, 2024).
We have developed a new bio-ink for 3D printing of engineered living materials. Various polymers (κ-carrageenan, sodium alginate, agar, and cellulose-based thickener) are mixed in precise amounts together with Chlamydomonas reinhardtii cells. This bioink could be used with other types of cells (e.g. bacteria, fungi, …) and used in a variety of applications of engineered living materials.
Additionally, we have investigated the coordinated flagellar swimming and the effect of external mechanical forces on C. reinhardtii. For this purpose, we have applied an external flow to selectively load mechanically each flagellum. We showed that the coordinated beating essentially only responds to mechanical load exerted on the cis flagellum (i.e. the flagellum that is organized by a basal body that develops from a pre-matured one in the mother cell); and that such asymmetry in response derives from a unilateral coupling between the two flagella (Wei D, et al. “The younger flagellum sets the beat for C. reinhardtii”, eLife, accepted for publication). We continue similar investigations to understand better the influence of external mechanical forces on C. reinhardtii, which will be instrumental to the development of microalgae-based living materials.
We have developed a new bio-ink for 3D printing of engineered living materials. Various polymers (κ-carrageenan, sodium alginate, agar, and cellulose-based thickener) are mixed in precise amounts together with Chlamydomonas reinhardtii cells. This bioink could be used with other types of cells (e.g. bacteria, fungi, …) and used in a variety of applications of engineered living materials.
Additionally, we have investigated the coordinated flagellar swimming and the effect of external mechanical forces on C. reinhardtii. For this purpose, we have applied an external flow to selectively load mechanically each flagellum. We showed that the coordinated beating essentially only responds to mechanical load exerted on the cis flagellum (i.e. the flagellum that is organized by a basal body that develops from a pre-matured one in the mother cell); and that such asymmetry in response derives from a unilateral coupling between the two flagella (Wei D, et al. “The younger flagellum sets the beat for C. reinhardtii”, eLife, accepted for publication). We continue similar investigations to understand better the influence of external mechanical forces on C. reinhardtii, which will be instrumental to the development of microalgae-based living materials.
In Oh JJ et al. 2024, we studied how the growth of microalgae depends on exposure to light, gas exchange, nutrient access and shape of the materials in microalgae-based photosynthetic engineered living materials (ELMs). It is broadly accepted that ELMs are an exciting new emerging material class that has the potential to revolutionize society. Amongst the many difficult challenges being tackled by scientists, the controlled growth of living organisms withing ELMs is one of the most important and it is crucial to bring ELMs beyond mere proof-of-concepts. Our study goes beyond state-of-the-arts by investigating and controlling the microalgae growth and spatial distribution in ELMs. We hope that it will motivate scientists to further investigate cell growth and associated emergent properties in this new class of materials.
In Wei D et al. 2024 (accepted for publication), we focussed on how the two inherently different flagella of the microalgae C. reinhardtii synchronize their beating. C. reinhardtii swims with a synchronous breaststroke-like motion of its flagella, and it modulates the beating amplitudes differentially to steer. For C. reinhardtii to move in specific directions, it is crucial that each of its two flagella respond differently to external stimuli. Due to the importance of such phenomena, the difference between the two flagella of C. reinhardtii has been investigated for decades. Despite these previous studies, it remains unclear how the flagella are coupled to each other and how each flagellum responds differently to external loads. This is mainly due to the difficulty in isolating one flagellum from the other, given the short distance between the two flagella. In this study, we have solved this problem by introducing a method to selectively load one flagellum by applying axial flows on single cells held in a specific orientation with a micropipette. We find that although both flagella beat in synchrony, the cis flagellum (i.e. “younger” one, as opposed to the “elder” trans that grows from mother basal body) leads the cell to synchronize with an external flow. This was evidenced by the fact that the coordinated beating essentially only responded to load exerted on the cis flagellum; and that such asymmetry in response derives from a unilateral coupling between the two flagella. This highlights an advanced function of the inter-flagellar mechanical coupling, and has implications for biflagellates’ tactic motility.
In Wei D et al. 2024 (accepted for publication), we focussed on how the two inherently different flagella of the microalgae C. reinhardtii synchronize their beating. C. reinhardtii swims with a synchronous breaststroke-like motion of its flagella, and it modulates the beating amplitudes differentially to steer. For C. reinhardtii to move in specific directions, it is crucial that each of its two flagella respond differently to external stimuli. Due to the importance of such phenomena, the difference between the two flagella of C. reinhardtii has been investigated for decades. Despite these previous studies, it remains unclear how the flagella are coupled to each other and how each flagellum responds differently to external loads. This is mainly due to the difficulty in isolating one flagellum from the other, given the short distance between the two flagella. In this study, we have solved this problem by introducing a method to selectively load one flagellum by applying axial flows on single cells held in a specific orientation with a micropipette. We find that although both flagella beat in synchrony, the cis flagellum (i.e. “younger” one, as opposed to the “elder” trans that grows from mother basal body) leads the cell to synchronize with an external flow. This was evidenced by the fact that the coordinated beating essentially only responded to load exerted on the cis flagellum; and that such asymmetry in response derives from a unilateral coupling between the two flagella. This highlights an advanced function of the inter-flagellar mechanical coupling, and has implications for biflagellates’ tactic motility.