The influence of cationic antiseptics on the processes of light energy conversion in various photosynthetic pigment-protein complexes

The widespread use of disinfectants and antiseptics, and consequently their release into the environment, determines the relevance of studying their potential impact on the main producers of organic matter on the planet-photosynthetic organisms. The review examines the effects of some biguanides and quaternary ammonium compounds, octenidine, miramistin, chlorhexidine, and picloxidine, on the functioning of the photosynthetic apparatus of various organisms (Strakhovskaya et al. in Photosynth Res 147:197-209, 2021; Knox et al. in Photosynth Res 153:103, 2022; Paschenko et al. in Photosynth Res 155:93-105, 2023a, Photosynth Res 2023b). A common feature of these antiseptics is the combination of hydrophobic and hydrophilic regions in the molecules, the latter carrying a positive charge(s). The comparison of the results obtained with intact bacterial membrane vesicles (chromatophores) and purified pigment-protein complexes (photosystem II and I) of oxygenic organisms allows us to draw conclusions about the mechanisms of the cationic antiseptic action on the functional properties of the components of the photosynthetic apparatus.

Use of bacterial photosynthetic vesicles to evaluate the effect of ionic liquids on the permeability of biological membranes

Ionic liquids (ILs) are salts composed of a combination of organic or inorganic cations and anions characterized by a low melting point, often below 100 °C. This property, together with an extremely low vapor pressure, low flammability and high thermal stability, makes them suitable for replacing canonical organic solvents, with a reduction of industrial activities impact on the environment. Although in the last decades the eco-compatibility of ILs has been extensively verified through toxicological tests performed on model organisms, a detailed understanding of the interaction of these compounds with biological membranes is far from being exhaustive. In this context, we have chosen to evaluate the effect of some ILs on native membranes by using chromatophores, photosynthetic vesicles that can be isolated from Rhodobacter capsulatus, a member of the purple non‑sulfur bacteria. Here, carotenoids associated with the light-harvesting complex II, act as endogenous spectral probes of the transmembrane electrical potential (ΔΨ). By measuring through time-resolved absorption spectroscopy the evolution of the carotenoid band shift induced by a single excitation of the photosynthetic reaction center, information on the ΔΨ dissipation due to ionic currents across the membrane can be obtained. We found that some ILs cause a rather fast dissipation of the transmembrane ΔΨ even at low concentrations, and that this behavior is dose-dependent. By using two different models to analyze the decay of the carotenoid signals, we attempted to interpret at a mechanistic level the marked increase of ionic permeability caused by specific ILs.

Exploring the mechanisms and impacts of melatonin on fish colouration

The pineal hormone melatonin is a multi-functional molecule with a recognized role in pigment aggregation in chromatophores, mediating its actions through binding to subtypes of its specific receptors. Since its discovery, melatonin has been known to be responsible for pigment aggregation towards the cell centre in fishes, including their embryos, as an adaptation to reduced light and thus results in pale body colouration. Diversity exists in the sensitivity of melanophores towards melatonin at interspecies, intraspecific levels, seasons, and amongst chromatophores at different regions of the animal body. In most of the fishes, melatonin leads to their skin paling at night. It is indicated that the melatonin receptors have characteristically maintained to show the same aggregating effects in fishes and other vertebrates in the evolutionary hierarchy. However, besides this aggregatory effect, melatonin is also responsible for pigment dispersion in certain fishes. Here is the demand in our review to explore further the nature of the dispersive behaviour of melatonin through the so-called β-melatonin receptors. It is clear that the pigment translocations in lower vertebrates under the effect of melatonin are mediated through the melatonin receptors coupled with other hormonal receptors as well. Therefore, being richly supplied with a variety of receptors, chromatophores and melanocytes can be used as in vitro test models for pharmacological applications of known and novel drugs. In this review, we present diverse effects of melatonin on chromatophores of fishes in particular with appropriate implications on most of the recent findings.

Mechanisms of alkali pH-shifted colour changes in squid (Uroteuthis edulis) subjected to frozen storage

The skin discoloration of squid subjected to frozen storage negatively affects market price. In this study, various alkali treatments were investigated for effects on red granules and yellow pigments of squid skin and corresponding mechanisms were investigated at the tissue, cellular and molecular level. A significant colour improvement was observed when subjected to a pH 12 treatment, supported by decreased Δb* and increased Δa* values. Neither lower nor harsher alkali treatments than pH 12 can not obtain such results. HE staining and the UV-vis spectrum suggest that the improved red colour in skin was ascribed to the release of red pigment granules from damaged chromatophores by alkaline treatment and the release of red pigments in alkaline aqueous solutions from granules. However, based on TEM and particle size analysis, an excessive alkali treatment of pH 13 would degrade granules into smaller particles. The degradation of yellowness pigments indicated high sensitivity to alkali environments according to HPLC results. This study provides a valuable reference for improving the colour appearance of squid skin subjected to frozen storage.

Tumor microenvironment responded naturally extracted FOF1-ATPase loaded chromatophores for antitumor therapy

Tumor microenvironment (TME) plays an important role in the growth, invasion, and metastasis of tumor cells. The pH of TME is more acidic in solid tumors than in normal tissues. Although targeted delivery in TME has progressed, the complex and expensive construction of delivery systems has limited their application. F_OF1-ATP synthase (F_OF1-ATPase) is a rotation molecular motor found in bacteria, chloroplasts, and mitochondria. Here, F_OF1-ATPase loaded chromatophores (chroma) isolated from thermophilic bacteria were extracted and utilized as a new delivery system targeting TME for the first time. Curcumin as model drug was successfully loaded by a filming-rehydration ultrasonic dispersion method to prepare a curcumin-loaded chroma delivery system (Cur-Chroma). The mobility and propensity distributions of Cur-Chroma reveal its specific pH-sensitive targeting driven by the transmembrane proton kinetic potential, demonstrating its distinct distribution in the TME and more favorable targeting delivery. Cellular uptake experiments indicated that Cur-Chroma entered cells through grid pathway-mediated endocytosis. In vivo studies have shown that Cur-Chroma can specifically target tumor tissue and effectively inhibit tumor growth with good safety. Curcumin's bioavailability and anti-tumor effects were significantly improved. These studies demonstrate that ATPase-loaded chromatophores are potentially ideal vehicles for anti-tumor drug delivery and have promising applications.

rubrum chromatophores

Photosynthetic membrane complexes of purple bacteria are convenient and informative macromolecular systems for studying the mechanisms of action of various physicochemical factors on the functioning of catalytic proteins both in an isolated state and as part of functional membranes. In this work, we studied the effect of cationic antiseptics (chlorhexidine, picloxydine, miramistin, and octenidine) on the fluorescence intensity and the efficiency of energy transfer from the light-harvesting LH1 complex to the reaction center (RC) of Rhodospirillum rubrum chromatophores. The effect of antiseptics on the fluorescence intensity and the energy transfer increased in the following order: chlorhexidine, picloxydine, miramistin, octenidine. The most pronounced changes in the intensity and lifetime of fluorescence were observed with the addition of miramistin and octenidine. At the same concentration of antiseptics, the increase in fluorescence intensity was 2-3 times higher than the increase in its lifetime. It is concluded that the addition of antiseptics decreases the efficiency of the energy migration LH1 → RC and increases the fluorescence rate constant k_fl. We associate the latter with a change in the polarization of the microenvironment of bacteriochlorophyll molecules upon the addition of charged antiseptic molecules. A possible mechanism of antiseptic action on R. rubrum chromatophores is considered. This work is a continuation of the study of the effect of antiseptics on the energy transfer and fluorescence intensity in chromatophores of purple bacteria published earlier in Photosynthesis Research (Strakhovskaya et al. in Photosyn Res 147:197-209, 2021).

The physiological cost of colour change: evidence, implications and mitigations

Animals benefit from phenotypic plasticity in changing environments, but this can come at a cost. Colour change, used for camouflage, communication, thermoregulation and UV protection, represents one of the most common plastic traits in nature and is categorised as morphological or physiological depending on the mechanism and speed of the change. Colour change has been assumed to carry physiological costs, but current knowledge has not advanced beyond this basic assumption. The costs of changing colour will shape the evolution of colour change in animals, yet no coherent research has been conducted in this area, leaving a gap in our understanding. Therefore, in this Review, we examine the direct and indirect evidence of the physiological cost of colour change from the cellular to the population level, in animals that utilise chromatophores in colour change. Our Review concludes that the physiological costs result from either one or a combination of the processes of (i) production, (ii) translocation and (iii) maintenance of pigments within the colour-containing cells (chromatophores). In addition, both types of colour change (morphological and physiological) pose costs as they require energy for hormone production and neural signalling. Moreover, our Review upholds the hypothesis that, if repetitively used, rapid colour change (i.e. seconds-minutes) is more costly than slow colour change (days-weeks) given that rapidly colour-changing animals show mitigations, such as avoiding colour change when possible. We discuss the potential implications of this cost on colour change, behaviour and evolution of colour-changing animals, generating testable hypotheses and emphasising the need for future work to address this gap.

The effect of some antiseptic drugs on the energy transfer in chromatophore photosynthetic membranes of purple non-sulfur bacteria Rhodobacter sphaeroides

Chromatophores of purple non-sulfur bacteria (PNSB) are invaginations of the cytoplasmic membrane that contain a relatively simple system of light-harvesting protein-pigment complexes, a photosynthetic reaction center (RC), a cytochrome complex, and ATP synthase, which transform light energy into the energy of synthesized ATP. The high content of negatively charged phosphatidylglycerol (PG) and cardiolipin (CL) in PNSB chromatophore membranes makes these structures potential targets that bind cationic antiseptics. We used the methods of stationary and kinetic fluorescence spectroscopy to study the effect of some cationic antiseptics (chlorhexidine, picloxydine, miramistin, and octenidine at concentrations up to 100 μM) on the spectral and kinetic characteristics of the components of the photosynthetic apparatus of Rhodobacter sphaeroides chromatophores. Here we present the experimental data on the reduced efficiency of light energy conversion in the chromatophore membranes isolated from the photosynthetic bacterium Rb. sphaeroides in the presence of cationic antiseptics. The addition of antiseptics did not affect the energy transfer between the light-harvesting LH1 complex and reaction center (RC). However, it significantly reduced the efficiency of the interaction between the LH2 and LH1 complexes. The effect was maximal with 100 μM octenidine. It has been proved that molecules of cationic antiseptics, which apparently bind to the heads of negatively charged cardiolipin molecules located in the rings of light-harvesting pigments on the cytoplasmic surface of the chromatophores, can disturb the optimal conditions for efficient energy migration in chromatophore membranes.

Morphological colour adaptation during development in fish: involvement of growth hormone receptor 1

Morphological background adaptation is both an endocrine and a nervous response, involving changes in the amount of chromatophores and pigment concentration. However, whether this adaptation takes place at early developmental stages is largely unknown. Somatolactin (Sl) is a pituitary hormone present in fish, which has been associated to skin pigmentation. Moreover, growth hormone receptor type 1 (Ghr1) has been suggested to be the Sl receptor and was associated with background adaptation in adults. In this context, the aim of this work was to evaluate the ontogeny of morphological adaptation to background and the participation of ghr1 in this process. We found in larval stages of the cichlid Cichlasoma dimerus that the number of head melanophores and pituitary cells immunoreactive to Sl was increased in individuals reared with black backgrounds compared with that in fish grown in white tanks. In larval stages of the medaka Oryzias latipes, a similar response was observed, which was altered by ghr1 biallelic mutations using CRISPR/Cas9. Interestingly, melanophore and leucophore numbers were highly associated. Furthermore, we found that somatic growth was reduced in ghr1 biallelic mutant O. latipes, establishing the dual function of this growth hormone receptor. Taken together, these results show that morphological background adaptation is present at early stages during development and that is dependent upon ghr1 during this period.

Incidence of the thermal transition in the range of 45-5°C in chromatophores present in the wings of Schistocerca americana

The variation of the color intensity of the chromatophores present in the wings of Schistocerca americana was analyzed by exposing 31 specimens to thermal transitions within the range of 45 - 5 °C.  The adult specimens were collected using a mini-terrarium of dimensions 40x40x30 cm. As a substrate, a layer of soil, stones, and finally a layer of grass were used along with branches of bushes and leaves; hydroponic lettuce, cabbage and the grass were used as food for the specimens. Optical microscopy of the wings of the insects was used for live observation without coverslips or contrasting substances. At 45°C, degradation of color intensity was observed in the chromatophores present in the wings. At 5°C, chromatophores intensify their color to brownish-black. This temperature was the extreme minimum that S. americana could tolerate. We found negative correlation between the temperature and the degree of darkness (R2 = 0.8038). Our results are in accordance with a previously published study in which Phaulacridium vittatum was examined, as the decrease of temperature caused darkening color change in melanin-type chromatophores. The present investigation can be considered as the first initial study of its kind for S. americana, in terms of examining the changes in the color intensity of the chromatophores present in the wings caused by thermal transition under laboratory conditions.

Histology and ultrastructure of the integumental chromatophores in tokay gecko (Gekko gecko) (Linnaeus, 1758) skin

This paper describes the relationship between the arrangement of dermal chromatophores in tokay gecko (Gekko gecko) skin and the formation of wild-type colouration, with emphasis on the ultrastructure of chromatophores. The samples of the tokay gecko skin were collected from wild-type colouration adult specimens. Morphology and distribution of chromatophores was determined by using light microscopy and transmission electron microscopy. The present study revealed that orange/red coloured skin of G. gecko contained erythrophores, which were located under basement membrane, and usually comprised deeper situated iridophores and melanophores which were form single layer with iridophores or were occupying the deepest region of dermis. In orange/red coloured skin, erythrophores were the predominant chromatophores. However in blue areas these cells occurred in small numbers or were not noticed at all. In blue pigmented areas predominated iridophores and melanophores. Iridophores were found just under basement membrane, but this superficial location of iridophores occured only in areas without erythrophores. Distribution of erythrophores, melanophores, and iridophores determines the characteristic blue colour of the tokay gecko skin with orange/red dots on the whole body.

A new mechanochemical model: coupled Ginzburg-Landau and Swift-Hohenberg equations in biological patterns of marine animals

In this work the skin coating of some vertebrate marine animals is modeled considering only dermis, epidermis and basal layers. The biological process takes into account: cellular diffusion of the epidermis, diffusion inhibition and long-range spatial interaction (nonlocal effect on diffusive dispersal) for cells of dermal tissue. The chemical and physical interactions between dermis and epidermis are represented by coupling quadratic terms and nonlinear terms additional. The model presents an interesting property associated with their gradient form: a connection between some physical, chemical and biological systems. The model equations proposed are solved with numerical methods to study the spatially stable emergent configurations. The spatiotemporal dynamic obtained of the numerical solution of these equations, present similarity with biological behaviors that have been found recently in the cellular movement of chromatophores (as contact-dependent depolarization and repulsion movement between melanophores, xanthophores and iridophores). The numerical solution of the model shows a great variety of beautiful patterns that are robust to changes of boundary condition. The resultant patterns are very similar to the pigmentation of some fish.

Functional characterisation of the chromatically antagonistic photosensitive mechanism of erythrophores in the tilapia Oreochromis niloticus

Non-visual photoreceptors with diverse photopigments allow organisms to adapt to changing light conditions. Whereas visual photoreceptors are involved in image formation, non-visual photoreceptors mainly undertake various non-image-forming tasks. They form specialised photosensory systems that measure the quality and quantity of light and enable appropriate behavioural and physiological responses. Chromatophores are dermal non-visual photoreceptors directly exposed to light and they not only receive ambient photic input but also respond to it. These specialised photosensitive pigment cells enable animals to adjust body coloration to fit environments, and play an important role in mate choice, camouflage and ultraviolet (UV) protection. However, the signalling pathway underlying chromatophore photoresponses and the physiological importance of chromatophore colour change remain under-investigated. Here, we characterised the intrinsic photosensitive system of red chromatophores (erythrophores) in tilapia. Like some non-visual photoreceptors, tilapia erythrophores showed wavelength-dependent photoresponses in two spectral regions: aggregations of inner pigment granules under UV and short-wavelengths and dispersions under middle- and long-wavelengths. The action spectra curve suggested that two primary photopigments exert opposite effects on these light-driven processes: SWS1 (short-wavelength sensitive 1) for aggregations and RH2b (rhodopsin-like) for dispersions. Both western blot and immunohistochemistry showed SWS1 expression in integumentary tissues and erythrophores. The membrane potential of erythrophores depolarised under UV illumination, suggesting that changes in membrane potential are required for photoresponses. These results suggest that SWS1 and RH2b play key roles in mediating intrinsic erythrophore photoresponses in different spectral ranges and this chromatically dependent antagonistic photosensitive mechanism may provide an advantage to detect subtle environmental photic change.

The influence of chromatic background on the photosensitivity of tilapia erythrophores

Non-mammalian vertebrates and invertebrates use extraretinal photoreceptors to detect light and perform diverse non-image-forming functions. Compared to well-studied visual systems, the effect of ambient light conditions on photosensory systems of extraretinal photoreceptors is poorly understood. Chromatophores are photosensitive dermal pigment cells that play an important role in the formation of body color patterns to fit the surrounding environment. Here, we used tilapia erythrophores to investigate the relationship between environmental light and chromatophore photoresponses. All erythrophores from three spectral conditions aggregated their pigment granules in UV/short wavelengths and dispersed in middle/long wavelengths. Unlike retinal visual systems, environmental light did not change the usage of the primary opsins responsible for aggregation and dispersion. In addition, short wavelength-rich and red-shifted background conditions led to an inhibitory effect on erythrophore photoresponses. We suggest that, as extraretinal photoreceptors for non-image-forming functions, chromatophores directly adjust their photoresponse sensitivity via changes in opsin expression levels rather than opsin types when environmental light changes.

Interaction between antimycin and cytochrome b560 in Chromatium chromatophores-The red shift of the absorption spectrum and photoreduction of cytochrome b560 in the presence of antimycin

In the presence of dithionite, which reduced all the cytochromes present in Chromatium chromatophores, the addition of antimycin caused a shift (1-2 nm) of the α band in the absorption spectrum of reduced cytochrome b560 toward longer wavelength. The difference spectrum (antimycin-added-minus-no addition) had a trough at 556 nm, a peak at 564 nm and an isosbestic point at 561 nm. The locations of the trough, peak and isosbestic point did not depend on the concentration of antimycin, but the amount of shifted cytochrome b560 increased as the concentration of antimycin increased. As reported previously, a single-turnover flash reduced cytochrome b560 in the presence of antimycin. The extent of the reduction depended on the concentration of antimycin. Both titrations of the red shift and the photoreduction of cytochrome b560 with antimycin fitted a first-order sigmoid curve with a half-maximum value at 5 × 10(-7) m of antimycin concentration. The results indicated that antimycin molecules interacted with, or were bound to, cytochrome b560 molecules in the ratio of one to one with an apparent dissociation constant of 3.5-7.3 × 10(-7) m.