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![Light focusing by cells of Synechocystis in air and water. The 3D ray-tracing models assume the cells have a homogeneous refractive index of 1.4. The short focus predicted with air around the cells (A) agrees with the experimental results and the 2D wave model presented by Schuergers et al. [1], but if we assume the cells are immersed in water (B), refraction is too weak to generate an intense focus on the cell membrane. Intensity plots (C,D) show the beam cross-section at the rear of the cell. The highly concentrated beam with the cell in air (C) is replaced by a very modest beam concentration when the external medium is assumed to be water (D). 3D ray-tracing provides a reasonable qualitative approximation despite the small size.](profile/Dan-Nilsson-2/publication/302778552/figure/fig2/AS:1014353360846850@1618852095370/Light-focusing-by-cells-of-Synechocystis-in-air-and-water-The-3D-ray-tracing-models.png)
Light focusing by cells of Synechocystis in air and water. The 3D ray-tracing models assume the cells have a homogeneous refractive index of 1.4. The short focus predicted with air around the cells (A) agrees with the experimental results and the 2D wave model presented by Schuergers et al. [1], but if we assume the cells are immersed in water (B), refraction is too weak to generate an intense focus on the cell membrane. Intensity plots (C,D) show the beam cross-section at the rear of the cell. The highly concentrated beam with the cell in air (C) is replaced by a very modest beam concentration when the external medium is assumed to be water (D). 3D ray-tracing provides a reasonable qualitative approximation despite the small size.
Source publication
It has been known for some time that not only animals, but also some advanced unicellular algae possess imaging eyes. Now it seems that even tiny cyanobacteria have what it takes to qualify for the most basic definition of vision.
Contexts in source publication
Context 1
... water outside, this difference drops to less than one-fifth compared to having air outside. This implies a more than five times longer focal length when the cell is immersed in water, and the concentration of light on the rear cell membrane becomes dramatically reduced (see simple modelling in Figure 2). The basic mechanism suggested for allowing phototaxis in Synechocystis [1] requires that light is substantially concentrated by focusing at the rear membrane. ...
Context 2
... basic mechanism suggested for allowing phototaxis in Synechocystis [1] requires that light is substantially concentrated by focusing at the rear membrane. Schuergers et al. [1] estimate the focus to be just below 0.5 mm wide, but in water it would become 2.25 mm at the rear of the cell (Figure 2), and the increase in light intensity a mere 1.8 times compared to almost 40 times with air outside the cell (accurate figures would require a 3D wave analysis). ...
Citations
... For example, the origin of vision, as an important organismal function, can be traced to the so-called "bacterial eye" and the principle of phototaxis (Scuergers et al., 2016). Vision in animals and other organisms is derived from this primordial bacterial cellular function (Nilsson and Colley, 2016). By analogy, cognition, as a wider function that integrates many other organismal functions, from sensing the environment to anticipation and decision-making, can equally be traced to first cells reaffirming the notion that cells are indivisible units of agency, sentience, and cognition Reber et al., 2023). ...
... This is inspired by a similar mechanism that has been suggested for the spherical cells of cyanobacterium Synechocystis sp. [113,114]. The illumination of these cells generates PJs at the shadow side, which are assumed to be perceived by a putative, well-distributed network of photoreceptors fixed on the plasma membrane, triggering a cellular signal transduction cascade ending by the flagella movement toward or outward from the light (see Figure 5 in [113]). ...
Siliceous diatom frustules present a huge variety of shapes and nanometric pore patterns. A better understanding of the light modulation by these frustules is required to determine whether or not they might have photobiological roles besides their possible utilization as building blocks in photonic applications. In this study, we propose a novel approach for analyzing the near-field light modulation by small pennate diatom frustules, utilizing the frustule of Gomphonema parvulum as a model. Numerical analysis was carried out for the wave propagation across selected 2D cross-sections in a statistically representative 3D model for the valve based on the finite element frequency domain method. The influences of light wavelength (vacuum wavelengths from 300 to 800 nm) and refractive index changes, as well as structural parameters, on the light modulation were investigated and compared to theoretical predictions when possible. The results showed complex interference patterns resulting from the overlay of different optical phenomena, which can be explained by the presence of a few integrated optical components in the valve. Moreover, studies on the complete frustule in an aqueous medium allow the discussion of its possible photobiological relevance. Furthermore, our results may enable the simple screening of unstudied pennate frustules for photonic applications.
... The next surprising discovery followed one year later, when Schuergers et al. (2016) reported prokaryotic bacterial vision in cyanobacterium Synechocystis sp. PCC 6803 [46][47][48][49]. Here, the whole cell acts as a lens, focusing light on a small patch of the plasma membrane ( Figure 3). ...
... In the case multi-cellular volvocine algae, light-focusing roles of cells affect the adjacent cells in a manner which participates in morphological symmetries and colony behavior as relevant information [50]. In Synechocystis, light perception at the photosensitive patch of the plasma membrane electrically controls type IV pili-based motility apparatus [51] in such a manner that pili close to the light focal spot are inactivated, whereas pili on the opposite side of the cell (facing the light source) are active and allow movement towards the light source [46][47][48][49]. As cyanobacteria evolved more than three billion years ago, it is obvious that this ancient prokaryotic vision based on the type IV pili complex is a very successful solution to their environmental challenges [52,53]. ...
Vision is essential for most organisms, and it is highly variable across kingdoms and domains of life. The most known and understood form is animal and human vision based on eyes. Besides the wide diversity of animal eyes, some animals such as cuttlefish and cephalopods enjoy so-called dermal or skin vision. The most simple and ancient organ of vision is the cell itself and this rudimentary vision evolved in cyanobacteria. More complex are so-called ocelloids of dinoflagellates which are composed of endocellular organelles, acting as lens- and cornea/retina-like components. Although plants have almost never been included into the recent discussions on organismal vision, their plant-specific ocelli had already been proposed by Gottlieb Haberlandt already in 1905. Here, we discuss plant ocelli and their roles in plant-specific vision, both in the shoots and roots of plants. In contrast to leaf epidermis ocelli, which are distributed throughout leaf surface, the root apex ocelli are located at the root apex transition zone and serve the light-guided root navigation. We propose that the plant ocelli evolved from the algal ocelloids, are part of complex plant sensory systems and guide cognition-based plant behavior.
... Compare the example of 'vision'. 'Vision' has been applied to systems as different to humans as individual bacteria (e.g., Nilsson & Colley 2016;Schuergers et al., 2016). Such claims generate comparatively little controversy: vision is not widely seen as a particularly ethically significant capacity; it has not been widely held to be unique to humans. ...
In recent philosophy of science there has been much discussion of both pluralism, which embraces scientific terms with multiple meanings, and eliminativism, which rejects such terms. Some recent work focuses on the conditions that legitimize pluralism over eliminativism – the conditions under which such terms are acceptable. Often, this is understood as a matter of encouraging effective communication – the danger of these terms is thought to be equivocation, while the advantage is thought to be the fulfilment of ‘bridging roles’ that facilitate communication between different scientists and specialisms. These theories are geared towards regulating communication between scientists qua scientists. However, this overlooks an important class of harmful equivocation that involves miscommunication between scientists and nonscientists, such as the public or policymakers. To make my case, I use the example of theory of mind, also known as ‘mindreading’ and ‘mentalizing’, and broadly defined as the capacity to attribute mental states to oneself and others. I begin by showing that ‘theory of mind’ has multiple meanings, before showing that this has resulted in harmful equivocations of a sort and in a way not accounted for by previous theories of pluralism and eliminativism.
... The photoreceptor proteins deactivate the type IV pili complexes near the focal point and activate the ones at the opposite side of the focal point, which leads the cell towards the light source in positive phototaxis. Modified/Adapted with permission from[143,157,160]. Copyright 2022 Elsevier. ...
In this review, the general background is provided on cyanobacteria, including morphology, cell membrane structure, and their photosynthesis pathway. The presence of cyanobacteria in nature, and their industrial applications are discussed, and their production of secondary metabolites are explained. Biofilm formation, as a common feature of microorganisms, is detailed and the role of cell diffusion in bacterial colonization is described. Then, the discussion is narrowed down to cyanobacterium Synechocystis, as a lab model microorganism. In this relation, the morphology of Synechocystis is discussed and its different elements are detailed. Type IV pili, the complex multi-protein apparatus for motility and cell-cell adhesion in Synechocystis is described and the underlying function of its different elements is detailed. The phototaxis behavior of the cells, in response to homogenous or directional illumination, is reported and its relation to the run and tumble statistics of the cells is emphasized. In Synechocystis suspensions, there may exist a reciprocal interaction between the cell and the carrying fluid. The effects of shear flow on the growth, doubling per day, biomass production, pigments, and lipid production of Synechocystis are reported. Reciprocally, the effects of Synechocystis presence and its motility on the rheological properties of cell suspensions are addressed. This review only takes up the general grounds of cyanobacteria and does not get into the detailed biological aspects per se. Thus, it is substantially more comprehensive in that sense than other reviews that have been published in the last two decades. It is also written not only for the researchers in the field, but for those in physics and engineering, who may find it interesting, useful, and related to their own research.
... Nilsson et. al. demonstrated that the focusing capability of Synechocystis was dramatically weakened in water as compared to that exposed in air 165 . This is because the changing from air to water induced a dramatic drop in the difference of refractive index inside and outside cell regions. ...
The rapid development of biophotonics and biomedical sciences makes a high demand on photonic structures to be interfaced with biological systems that are capable of manipulating light at small scales for sensitive detection of biological signals and precise imaging of cellular structures. However, conventional photonic structures based on artificial materials (either inorganic or toxic organic) inevitably show incompatibility and invasiveness when interfacing with biological systems. The design of biophotonic probes from the abundant natural materials, particularly biological entities such as virus, cells and tissues, with the capability of multifunctional light manipulation at target sites greatly increases the biocompatibility and minimizes the invasiveness to biological microenvironment. In this review, advances in biophotonic probes for bio-detection and imaging are reviewed. We emphatically and systematically describe biological entities-based photonic probes that offer appropriate optical properties, biocompatibility, and biodegradability with different optical functions from light generation, to light transportation and light modulation. Three representative biophotonic probes, i.e., biological lasers, cell-based biophotonic waveguides and bio-microlenses, are reviewed with applications for bio-detection and imaging. Finally, perspectives on future opportunities and potential improvements of biophotonic probes are also provided.
... 13,15,16 Moreover, research done on the visual capabilities of algae and protists clearly suggest vision already in unicellular organisms. [17][18][19][20][21][22][23] Experimental testing of the ocelli-based plant vision, as it was done by Harold Wager, 4 would be the logical next step in our quest for understanding the plant sensory complexity. Black bars correspond to non-mimic leaves (control), without contact with plastic leave. ...
Upon discovery that the Boquila trifoliolata is capable of flexible leaf mimicry, the question of the mechanism behind this ability has been unanswered. Here, we demonstrate that plant vision possibly via plant-specific ocelli is a plausible hypothesis. A simple experiment by placing an artificial vine model above the living plants has shown that these will attempt to mimic the artificial leaves. The experiment has been carried out with multiple plants, and each plant has shown attempts at mimicry. It was observed that mimic leaves showed altered leaf areas, perimeters, lengths, and widths compared to non-mimic leaves. We have calculated four morphometrical features and observed that mimic leaves showed higher aspect ratio and lower rectangularity and form factor compared to non-mimic leaves. In addition, we have observed differences in the leaf venation patterns, with the mimic leaves having less dense vascular networks, thinner vascular strands, and lower numbers of free-ending veinlets.
... For example, an eye-less strain of Chlamydomonas [342] or multicellular Dictyostelium slugs [343,344] can focus and align with directional light. In prokaryotes, this mechanism has only been described in cyanobacteria, which operate at the physical limit of focusing [56,345]. ...
All living cells interact dynamically with a constantly changing world. Eukaryotes, in particular, evolved radically new ways to sense and react to their environment. These advances enabled new and more complex forms of cellular behaviour in eukaryotes, including directional movement, active feeding, mating, and responses to predation. But what are the key events and innovations during eukaryogenesis that made all of this possible? Here we describe the ancestral repertoire of eukaryotic excitability and discuss five major cellular innovations that enabled its evolutionary origin. The innovations include a vastly expanded repertoire of ion channels, the emergence of cilia and pseudopodia, endomembranes as intracellular capacitors, a flexible plasma membrane and the relocation of chemiosmotic ATP synthesis to mitochondria, which liberated the plasma membrane for more complex electrical signalling involved in sensing and reacting. We conjecture that together with an increase in cell size, these new forms of excitability greatly amplified the degrees of freedom associated with cellular responses, allowing eukaryotes to vastly outperform prokaryotes in terms of both speed and accuracy. This comprehensive new perspective on the evolution of excitability enriches our view of eukaryogenesis and emphasizes behaviour and sensing as major contributors to the success of eukaryotes.
This article is part of the theme issue ‘Basal cognition: conceptual tools and the view from the single cell’.
... For example, an eye-less strain of Chlamydomonas [317] or multicellular Dictyostelium slugs [318,319] can focus and align with directional light. In prokaryotes this mechanism was only described in cyanobacteria, which operate at the physical limit of focusing [49,320]. ...
All living cells interact dynamically with a constantly changing world. Eukaryotes in particular, evolved radically new ways to sense and react to their environment. These advances enabled new and more complex forms of cellular behavior in eukaryotes, including directional movement, active feeding, mating, or responses to predation. But what are the key events and innovations during eukaryogenesis that made all of this possible? Here we describe the ancestral repertoire of eukaryotic excitability and discuss five major cellular innovations that enabled its evolutionary origin. The innovations include a vastly expanded repertoire of ion channels, endomembranes as intracellular capacitors, a flexible plasma membrane, the emergence of cilia and pseudopodia, and the relocation of chemiosmotic ATP synthesis to mitochondria that liberated the plasma membrane for more complex electrical signaling involved in sensing and reacting. We conjecture that together with an increase in cell size, these new forms of excitability greatly amplified the degrees of freedom associated with cellular responses, allowing eukaryotes to vastly outperform prokaryotes in terms of both speed and accuracy. This comprehensive new perspective on the evolution of excitability enriches our view of eukaryogenesis and emphasizes behaviour and sensing as major contributors to the success of eukaryotes.
... But that does not show they are physical. 31 For the qualifications in "almost," see Nilsson and Colley (2016). ...
