Color sensitive retina based on bacteriorhodopsin

Hypersaline environments as natural sources of microbes with potential applications in biotechnology: The case of solar evaporation systems to produce salt in Alicante County (Spain)

Extremophilic microbes show a unique metabolism due to the adaptations they display to deal with extreme environmental parameters characterizing the extreme ecosystems that they inhabit (high salt concentration, high temperatures, and extreme pH values, high exposure to solar radiation etc.). Halophilic microorganisms characterised and isolated from saltmarshes, brines, salted ponds, salty lagoons etc. have recently attracted attention due to their potential biotechnological applications (as whole cells used for different purposes like wastewater treatments, or their biomolecules: enzymes, antibiotics, carotenoids, bioplastics). Alicante county (southeast of Spain) accounts for a significant number of salty environments like coastal or inland salty ponds from where sodium chloride (NaCl)is obtained, marshes, salty lagoons, etc. The best system characterised so far from a microbiological point of view is "Salinas de Santa Pola", also termed "Salinas Bras del Port". However, there are many other salty environments to be explored, like the natural park of Torrevieja and la Mata lagoons, salty lagoon located in Calpe city or inland salted ponds like those located in the northwest of the county. This review summarises the most relevant biotechnological applications of halophilic microbes described up to now. In addition, special attention is focused on ecosystems such as the lagoons of Torrevieja or inland salt marshes as natural environments whose microbial biodiversity is worthy of being studied in search of new strains and species with the aim to analyze their potential biotechnological applications (pharmaceutical, food industry, biomedicine, etc.).

A Light-Driven Integrated Bio-Capacitor with Single Nano-Channel Modulation

Bioelectronics, an emerging discipline formed by the biology and electronic information disciplines, has maintained a state of rapid development since its birth. Amongst the various functional bioelectronics materials, bacteriorhodopsin (bR), with its directional proton pump function and favorable structural stability properties, has drawn wide attention. The main contents of the paper are as follows: Inspired by the capacitive properties of natural protoplast cell membranes, a new bio-capacitor based on bR and artificial nanochannels was constructed. As a point of innovation, microfluidic chips were integrated into our device as an ion transport channel, which made the bio-capacitor more stable. Meanwhile, a single nanopore structure was integrated to improve the accuracy of the device structure. Experiments observed that the size of the nanopore affected the ion transmission rate. Consequently, by making the single nanopore’s size change, the photocurrent duration time (PDT) of bR was effectively regulated. By using this specific phenomenon, the original transient photocurrent was successfully transformed into a square-like wave.

Bio-inspired strategies for next-generation perovskite solar mobile power sources

Smart electronic devices are becoming ubiquitous due to many appealing attributes including portability, long operational time, rechargeability and compatibility with the user-desired form factor. Integration of mobile power sources (MPS) based on photovoltaic technologies with smart electronics will continue to drive improved sustainability and independence. With high efficiency, low cost, flexibility and lightweight features, halide perovskite photovoltaics have become promising candidates for MPS. Realization of these photovoltaic MPS (PV-MPS) with unconventionally extraordinary attributes requires new 'out-of-box' designs. Natural materials have provided promising designing solutions to engineer properties under a broad range of boundary conditions, ranging from molecules, proteins, cells, tissues, apparatus to systems in animals, plants, and humans optimized through billions of years of evolution. Applying bio-inspired strategies in PV-MPS could be biomolecular modification on crystallization at the atomic/meso-scale, bio-structural duplication at the device/system level and bio-mimicking at the functional level to render efficient charge delivery, energy transport/utilization, as well as stronger resistance against environmental stimuli (e.g., self-healing and self-cleaning). In this review, we discuss the bio-inspired/-mimetic structures, experimental models, and working principles, with the goal of revealing physics and bio-microstructures relevant for PV-MPS. Here the emphasis is on identifying the strategies and material designs towards improvement of the performance of emerging halide perovskite PVs and strategizing their bridge to future MPS.

A Review on Bacteriorhodopsin-Based Bioelectronic Devices

Bacteriorhodopsin protein extracted from Halobacterium salinarum is widely used in many biohybrid electronic devices and forms a research subject known as bioelectronics, which merges biology with electronic technique. The specific molecule structure and components of bR lead to its unique photocycle characteristic, which consists of several intermediates (bR, K, L, M, N, and O) and results in proton pump function. In this review, working principles and properties of bacteriorhodopsin are briefly introduced, as well as bR layer preparation method. After that, different bR-based devices divided into photochemical and photoelectric applications are shown. Finally, outlook and conclusions are drawn to inspire new design of high-performance bR-based biohybrid electronic devices.

The current state of the brain-computer interface problem

It was only 40 years ago that the first PC appeared. Over this period, rather short in historical terms, we have witnessed the revolutionary changes in lives of individuals and the entire society. Computer technologies are tightly connected with any field, either directly or indirectly. We can currently claim that computers are manifold superior to a human mind in terms of a number of parameters; however, machines lack the key feature: they are incapable of independent thinking (like a human). However, the key to successful development of humankind is collaboration between the brain and the computer rather than competition. Such collaboration when a computer broadens, supplements, or replaces some brain functions is known as the brain-computer interface. Our review focuses on real-life implementation of this collaboration.

Novel interfaces for light directed neuronal stimulation: advances and challenges

Light activation of neurons is a growing field with applications ranging from basic investigation of neuronal systems to the development of new therapeutic methods such as artificial retina. Many recent studies currently explore novel methods for optical stimulation with temporal and spatial precision. Novel materials in particular provide an opportunity to enhance contemporary approaches. Here we review recent advances towards light directed interfaces for neuronal stimulation, focusing on state-of-the-art nanoengineered devices. In particular, we highlight challenges and prospects towards improved retinal prostheses.

Potential applications of bacteriorhodopsin mutants

Bacteriorhodopsin (BR), a model system in biotechnology, is a G-protein dependent trans membrane protein which serves as a light driven proton pump in the cell membrane of Halobacterium salinarum. Due to the linkage of retinal to the protein, it seems colored and has numbers of versatile properties. As in vitro culture of the Halobacteria is very difficult, and isolation is time consuming and usually inefficient, production of genetically modified constructs of the protein is essential. There are three important characteristics based on protein catalytic cycle and molecular functions of photo-electric, photochromic and proton transporting, which makes this protein as a strategic molecule with potential applications in biotechnology. Such applications include protein films, used in artificial retinal implants, light modulators, three-dimensional optical memories, color photochromic sensors, photochromic and electrochromic papers and ink, biological camouflage and photo detectors for biodefense and non-defense purposes.

Isolation and functional expression of the bop gene from Halobiforma lacisalsi

A novel bop gene was described from Halobiforma lacisalsi strain AJ5(T), an extremely halophilic archaeon isolated from Ayakekum Lake, China. Following six rounds of PCR amplification based on the conserved fragment of the bop gene, the complete sequence of the bop gene, including the 5' and 3' flanking regions of the conserved fragment, was obtained by the ligation-mediated PCR amplification (LPA) approach. The data presented provide us with further insight into the distribution of bop-like genes in the family Halobacteriaceae. This is the first example of a bop-like gene in halophiles found in the high-pH environment. Alignment and hydropathy analysis of the deduced amino acid sequence identified the conserved functional sites as well as some variations compared with other bacterio-opsins. Molecular phylogenetic analysis revealed the position of the bacterio-opsin of strain AJ5, which is closest to that of Haloterrigena sp. arg-4 with 85% identity. In the presence of all-trans retinal, recombinant Escherichia coli cells expressing the gene turned dark purple. The purple membrane from the recombinant E. coli showed maximal absorption at 540 nm.

Genetic cloning and functional expression in Escherichia coli of an archaerhodopsin gene from Halorubrum xinjiangense

Pairs of PCR primers that targeted the archae/bacteriorhodopsin gene were used to clone the archaerhodopsin (aR) gene of Halorubrum xinjiangense strain BD-1(T), and this gene was sequenced and functionally expressed in Escherichia coli. Recombinant E. coli cells harboring the plasmid carrying this gene became slightly purple or blue depending on whether they were supplemented with all- trans retinal or 3,4-dihydroretinal, respectively, during induction with IPTG. The purple and blue membranes from the recombinant E. coli showed maximal absorption at 555 and 588 nm, respectively, which are different from maximal absorption at 568 nm of the wild-type purple membrane. Purple membranes from the recombinant E. coli and from strain BD-1(T) were investigated in parallel. The E. coli purple membrane was fabricated into films and photoelectric responses were observed that depended on the light-on and light-off stimuli.

Isolation and characterization of a novel strain of Natrinema containing a bop gene

A novel member of extremely halophilic archaea, strain AJ2, was isolated from Ayakekum Lake located in Altun Mountain National Nature Reserve of Xinjiang Uygur Autonomous Region in China. The strain AJ2 requires at least 10% (w/v) NaCl and grows 10% to 30% (optimum at 20%). Phylogenetic analysis based on 16S rDNA sequence comparison revealed that strain AJ2 clustered to three Natrinema species with less than 97.7% sequence similarities, suggesting AJ2 is a novel member of Natrinema. A bacteriorhodopsin-encoding (bop) gene was subsequently detected in the AJ2 genome using the polymerase chain reaction technique. The cloning and sequencing of a 401 base pairs fragment indicated the deduced amino acid sequence of bop from AJ2 is different from that reported for bacteriorhodopsins. This is the first reported detection of a bop gene in Natrinema.

Light adaptation of bacteriorhodopsin correlates with dielectric spectral kinetics in purple membrane

The retinal protein, bacteriorhodopsin (bR), has several potential bioelectronic applications and it is considered as a model for G-protein coupled receptors. Its electrical parameters, therefore, deserve particular attention. Such parameters could be determined by virtue of studying its dielectric spectrum in the low frequency range (20 Hz-1 MHz). The kinetics of dark-light adaptation of bR is reported in terms of electrical parameters of the purple membrane (PM) containing bR. The data have exhibited sudden pronounced increase in the ac-conductivity, upon illuminating the dark-adapted bR (DA-bR), which may be considered in further implications of bR for biotechnological applications. These changes turned out to be composed of, at least, two growing exponential components: one relatively fast followed by slower one. Their lifetime ratio exhibited decreases with increasing the frequency; meanwhile, their amplitude ratio displayed very exciting behavior at significant frequencies. This may correlate the kinetics of light adaptation to relaxations in PM. Moreover, the light adaptation has been observed to cause initial fast and large decreases in dc-conductivity with subsequent slower and smaller decreases. Changing the conductivity during the time of light adaptation reflects changes in the surface charge of the PM. The lifetimes of these events, therefore, help follow the kinetics of the pathway of conformational changes that might be occurring during light adaptation. The dipole moment (permanent and induced) of PM, in addition to, its size showed one exponential growth of comparable lifetime (approximately 7 min) during the light adaptation. The variation in PM size from dark to light state should be in keeping with that diffusion may influence the three-dimensional data storage in data processing based on bR.

Effect of beta-particles on the retinal chromophore in bacteriorhodopsin of Halobacterium salinarium

Bacteriorhodopsin (bR) is an attractive intelligent material. Understanding the mechanism of its light-driven proton pumping outward the cell implicates it in many technical applications, particularly, in what is called optical computers, and the biotechnology is waiting for this promised biological molecule. An ionizing radiation source handling could be computerized in radiation fields. The computer containing such biological material will not be out of reach of the fields of ionizing radiation. So it is interesting to report on the working of such biological computer if it is subjected to ionizing radiation. The functional unit in this molecule is retinal chromophore. In the present work, it is interested to assess the functionality of bR through determining the electronic transition dipole moment of its chromophore. Significant changes in the values of the absorption transition dipole moment were noticed at different doses of beta-particles in the range of 0.1-0.3 kGy. Ionizing radiation-induced changes in bR were followed by intrinsic fluorescence spectroscopy. An analysis of the fluorescence data bears on the tertiary structure of bR. The emission spectrum is, however, red shifted with an increase in intensity with the different doses; in the meanwhile, gradual decrease in the visible absorbance has occurred till almost complete loss is attained. This bleaching due to ionizing radiation may offer an alternative way of data processing in such optical devices based on bR. Nevertheless, bR has proofed to be used as a biological indicator of ionizing radiation. However, the potential of bR for use as a biosensor to detect ionizing radiation should be considered.

Kinetics of photo-active bacteriorhodopsin analog 3,4-didehydroretinal

Kinetics of the photo-induced processes of the transient states of the 3,4-didehydroretinal (3,4-dhr) modified bacteriorhodopsin (bR) was studied by a flash photolysis method in a water suspension at room temperature. The excitation initiated a photocycle with several transient intermediates similar to the trans photocycle of native bR. The main observation of the study was that although major part (80%) of the population of the M state relaxed via the O intermediate as in natural bR, 20% relaxed directly to the bR ground state in 200 ms.