Cyanobacteria, also known as Cyanophyta, are a phylum of Gram-negative bacteria that obtain energy via photosynthesis. The name cyanobacteria refers to their color, which similarly forms the basis of cyanobacteria's common name, blue-green algae. They appear to have originated in a freshwater or terrestrial environment. Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria.
Phycobilins are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Most of their molecules consist of a chromophore which makes them coloured. They are unique among the photosynthetic pigments in that they are bonded to certain water-soluble proteins, known as phycobiliproteins. Phycobiliproteins then pass the light energy to chlorophylls for photosynthesis.
Prochlorococcus is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation. These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth. Prochlorococcus microbes are among the major primary producers in the ocean, responsible for a large percentage of the photosynthetic production of oxygen. Prochlorococcus strains, called ecotypes, have physiological differences enabling them to exploit different ecological niches. Analysis of the genome sequences of Prochlorococcus strains show that 1,273 genes are common to all strains, and the average genome size is about 2,000 genes. In contrast, eukaryotic algae have over 10,000 genes.
Phycoerythrin (PE) is a red protein-pigment complex from the light-harvesting phycobiliprotein family, present in red algae and cryptophytes, accessory to the main chlorophyll pigments responsible for photosynthesis.The red pigment is due to the prosthetic group, phycoerythrobilin, which gives phycoerythrin its red color.
Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll a. They include other forms of this pigment, such as chlorophyll b in green algal and higher plant antennae, while other algae may contain chlorophyll c or d. In addition, there are many non-chlorophyll accessory pigments, such as carotenoids or phycobiliproteins, which also absorb light and transfer that light energy to photosystem chlorophyll. Some of these accessory pigments, in particular the carotenoids, also serve to absorb and dissipate excess light energy, or work as antioxidants. The large, physically associated group of chlorophylls and other accessory pigments is sometimes referred to as a pigment bed.
Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist within the membrane like carotenoids can. Instead, phycobiliproteins aggregate to form clusters that adhere to the membrane called phycobilisomes. Phycocyanin is a characteristic light blue color, absorbing orange and red light, particularly near 620 nm, and emits fluorescence at about 650 nm. Allophycocyanin absorbs and emits at longer wavelengths than phycocyanin C or phycocyanin R. Phycocyanins are found in cyanobacteria. Phycobiliproteins have fluorescent properties that are used in immunoassay kits. Phycocyanin is from the Greek phyco meaning “algae” and cyanin is from the English word “cyan", which conventionally means a shade of blue-green and is derived from the Greek “kyanos" which means a somewhat different color: "dark blue". The product phycocyanin, produced by Aphanizomenon flos-aquae and Spirulina, is for example used in the food and beverage industry as the natural coloring agent 'Lina Blue' or 'EXBERRY Shade Blue' and is found in sweets and ice cream. In addition, fluorescence detection of phycocyanin pigments in water samples is a useful method to monitor cyanobacteria biomass.
Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes. It was lost in the plastids of green algae / plants (chloroplasts).
Allophycocyanin is a protein from the light-harvesting phycobiliprotein family, along with phycocyanin, phycoerythrin and phycoerythrocyanin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble and therefore cannot exist within the membrane like carotenoids, but aggregate, forming clusters that adhere to the membrane called phycobilisomes. Allophycocyanin absorbs and emits red light, and is readily found in Cyanobacteria, and red algae. Phycobilin pigments have fluorescent properties that are used in immunoassay kits. In flow cytometry, it is often abbreviated APC. To be effectively used in applications such as FACS, High-Throughput Screening (HTS) and microscopy, APC needs to be chemically cross-linked.
Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae. They capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores. They are most important constituents of the phycobilisomes.
Phycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of which it is the terminal acceptor of energy. The amount of phycoerythrobilin in phycoerythrins varies a lot, depending on the considered organism. In some Rhodophytes and oceanic cyanobacteria, phycoerythrobilin is also present in the phycocyanin, then termed R-Phycocyanin. Like all phycobilins, phycoerythrobilin is covalently linked to these phycobiliproteins by a thioether bond.
A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a series of protein-bound co-factors. These co-factors are light-absorbing molecules (also named chromophores or pigments) such as chlorophyll and pheophytin, as well as quinones. The energy of the photon is used to excite an electron of a pigment. The free energy created is then used, via a chain of nearby electron acceptors, for a transfer of hydrogen atoms (as protons and electrons) from H2O or hydrogen sulfide towards carbon dioxide, eventually producing glucose. These electron transfer steps ultimately result in the conversion of the energy of photons to chemical energy.
A light-harvesting complex consists of a number of chromophores which are complex subunit proteins that may be part of a larger super complex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to collect more of the incoming light than would be captured by the photosynthetic reaction center alone. The light which is captured by the chromophores is capable of exciting molecules from their ground state to a higher energy state, known as the excited state. This excited state does not last very long and is known to be short-lived.
Photosynthetic picoplankton or picophytoplankton is the fraction of the phytoplankton performing photosynthesis composed of cells between 0.2 and 2 µm in size (picoplankton). It is especially important in the central oligotrophic regions of the world oceans that have very low concentration of nutrients.
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 to 1.5 µm. The photosynthetic coccoid cells are preferentially found in well–lit surface waters where it can be very abundant. Many freshwater species of Synechococcus have also been described.
Cyanophages are viruses that infect cyanobacteria, also known as Cyanophyta or blue-green algae. Cyanobacteria are a phylum of bacteria that obtain their energy through the process of photosynthesis. Although cyanobacteria metabolize photoautotrophically like eukaryotic plants, they have prokaryotic cell structure. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. The size of the head and tail vary among species of cyanophages. Cyanophages infect a wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in eutrophic freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to Synechococcus spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles.
Phycoerythrocyanin is a kind of phycobiliprotein, magenta chromoprotein involved in photosynthesis of some Cyanobacteria. This chromoprotein consists of alpha- and beta-subunits, generally aggregated as hexamer. Alpha-phycoerythrocyanin contains a phycoviolobilin, a violet bilin, that covalently attached at Cys-84, and beta-phycoerythrocyanin contains two phycocyanobilins, a blue bilin, that covalently attached at Cys-84 and -155, respectively. Phycoerythrocyanin is similar to phycocyanin, an important component of the light-harvesting complex (phycobilisome) of cyanobacteria and red algae.
Photosynthetic reaction centre proteins are main protein components of photosynthetic reaction centres (RCs) of bacteria and plants. They are transmembrane proteins embedded in the chloroplast thylakoid or bacterial cell membrane.
Orange carotenoid protein (OCP) is a water-soluble protein which plays a role in photoprotection in diverse cyanobacteria. It is the only photoactive protein known to use a carotenoid as the photoresponsive chromophore. The protein consists of two domains, with a single keto-carotenoid molecule non-covalently bound between the two domains. It is a very efficient quencher of excitation energy absorbed by the primary light-harvesting antenna complexes of cyanobacteria, the phycobilisomes. The quenching is induced by blue-green light. It is also capable of preventing oxidative damage by directly scavenging singlet oxygen (1O2).
Biliproteins are pigment protein compounds that are located in photosynthesising organisms such as algae and certain insects. They refer to any protein that contains a bilin chromophore. In plants and algae, the main function of biliproteins is to make the process of light accumulation required for photosynthesis more efficient; while in insects they play a role in growth and development. Some of their properties: including light-receptivity, light-harvesting and fluorescence have made them suitable for applications in bioimaging and as indicators; while other properties such as anti-oxidation, anti-aging and anti-inflammation in phycobiliproteins have given them potential for use in medicine, cosmetics and food technology. While research on biliproteins dates back as far as 1950, it was hindered due to issues regarding biliprotein structure, lack of methods available for isolating individual biliprotein components, as well as limited information on lyase reactions . Research on biliproteins has also been primarily focused on phycobiliproteins; but advances in technology and methodology, along with the discovery of different types of lyases, has renewed interest in biliprotein research, allowing new opportunities for investigating biliprotein processes such as assembly/disassembly and protein folding.
Alexander Glazer was a Professor of the Graduate School in the Department of Molecular and Cell Biology at the University of California, Berkeley. He had a passion for protein chemistry and structure function relationships. He also had a longstanding interest in light-harvesting complexes in cyanobacteria and red algae called phycobilisomes. He had also spent more than 10 years working on the human genome project where he has investigated methods for DNA detection and sequencing which most notably includes the development of fluorescent reagents involved in cell labeling. Most recently, he had focused his studies on issues in environmental sciences. He died on July 18, 2021 in Orinda, California
