Underwater Light Manipulation by the Benthic Diatom Ctenophora pulchella: From PAR Efficient Collection to UVR Screening

Abstract

Several species of diatoms, unicellular microalgae which constitute the main component of phytoplankton, are characterized by an impressive photosynthetic efficiency while presenting a noticeable tolerance versus exposure to detrimental UV radiation (UVR). In particular, the growth rate of the araphid diatom Ctenophora pulchella is not significantly affected by harsh treatments with UVR, even in absence of detectable, specific UV-absorbing pigments and even if it is not able to avoid high UV exposure by motility. In this work we applied a multi-disciplinary approach involving numerical computation, photonics, and biological parameters in order to investigate the possible role of the frustule, micro- and nano-patterned silica shell which encloses the cell, in the ability of C. pulchella to efficiently collect photosynthetic active radiation (PAR) and to simultaneously screen the protoplasm from UVR. The characterization of the photonic properties of the frustule has been accompanied by in vivo experiments conducted in water in order to investigate its function as optical coupler between light and plastids.

Numerical Analysis of the Light Modulation by the Frustule of Gomphonema parvulum: The Role of Integrated Optical Components

“…The PJ associated with the nodule (the maximum D ) is expected to be higher in intensity and interrupts the interference pattern, as shown in Figure 8 . This PJ is similar to the focusing beam observed by De Tommasi et al [ 29 ]. The intense light focalization might give the PJ—especially that associated with the nodule—potential in several applications to, for instance, enhance the resolution of optical microscopy, reach super-resolution imaging, enhance Raman scattering, improve fluorescence spectroscopy, enable subwavelength photolithography, and enhance the optical absorption in optoelectronic devices [ 80 , 81 ].…”

“…Moreover, unlike in large valves, such as those of Coscinodiscus spp., where the edge diffraction is less significant [ 96 ], in finite-size valves, the edge diffraction significantly contributes to the light interference pattern. A similar conclusion was obtained for the valve of pennate diatom Ctenophora pulchella of narrow width (see Figure 2 in [ 29 ]). The contribution of thickened areas within the valve (such as the nodule in GP) to the obtained interference pattern suggests that, even in the case of large valves with complex ultrastructures, such as the valves of Arachnoidiscus spp.…”

“…During the last two decades, light propagation across a number of diatom valves belonging to a few species was investigated by employing theoretical and experimental approaches, and these efforts have been reviewed [ 22 , 24 , 27 ]. These studies demonstrated the valves’ ability to influence the propagation of light through, for instance, focusing [ 28 , 29 , 30 ], orientation-dependent [ 31 , 32 ] and wavelength-dependent transmission [ 33 ], waveguiding [ 34 , 35 ], guided-mode resonance [ 36 ], and diffraction grating behavior in the far field [ 37 , 38 ], in addition to their intrinsic photoluminescence properties [ 39 , 40 ]. Recently, light interaction with a girdle band has also been reported, showing a photonic pseudogap associated with its photonic crystal structure [ 41 ].…”

“…However, it is difficult to make general assumptions about valves’ light modulation capabilities or frustules’ photobiological roles that are valid for the huge number of diatom species (there might be up to 10 5 species), which have considerable variation in frustule shape and ultrastructure, especially since many diatoms have a small size with different pore patterns, and many species belong to the group of pennates, as indicated by the AlgaeBase website [ 44 ]. Recently, the pennate species received some attention through the investigation of the light modulation by the araphid pennate frustule of Ctenophora pulchella [ 29 ]. It is worth mentioning that some application studies considered pennate diatom valves; however, they were often more concerned with a specific feature (such as photoluminescence or guided-mode resonance) and did not analyze all their light modulation capabilities [ 36 , 45 ].…”

Warming exacerbates the impacts of ultraviolet radiation in temperate diatoms but alleviates the effect on polar species

“…19,20 Photosystem II catalyzes the photo-oxidation of water using light energy and plays a central role in the conversion of energy from photons trapped by pigments into electron flow to generate chemical energy used to drive the fixation of carbon dioxide. 21 In contrast to Photosystem I (PSI), PSII has been reported to be extremely sensitive to physical stressors, especially UVR and high-intensity PAR, 22,23 and can be damaged by UVR. 24 To maintain efficient photosynthetic performance, the damaged PSII subunits need to be replaced by de-novo-synthesized proteins, 25 which involves a series of enzyme-catalyzed reactions, and thus is also sensitive to temperature changes.…”