The main source for food and oxygen are cyanobacteria and chloroplasts that do photosynthesis. Cyanobacteria are essential for the nitrogen cycle, and so to transform nitrogen in the atmosphere into useful form for organisms to make the basic building blocks for life. The end product of photosynthesis is glucose, - needed as food source for almost all life forms. For a proponent that life took millions of years to emerge gradually and biodiversity as well, and so cyanobacteria and chloroplasts, that came hundreds of millions of years after life started, that is a hudge problem. No oxygen in the atmosphere, and UV radiation would kill the organisms. Nor could they emerge without a adequate food source. Looking everything in that perspective, it makes a lot of sense to believe God created everything in six days. And created the atmosphere with oxygen , and the nitrogen cycle fully setup, and plants and animals like cyanobacteria, essential in the food chain and nitrogen cycle. That would solve the - problem of nutrition, - the problem of UV radiation - and the problem of the nitrogen source required for life.
The existence in the same organism of cyanobacterias of two conflicting metabolic systems, oxygen evolving photosynthesis and oxygen-sensitive nitrogen fixation, is a puzzling paradox. Explanations are pure guesswork.
Researchers have long been puzzled as to how the cyanobacteria could make all that oxygen without poisoning themselves. To avoid their DNA getting wrecked by a hydroxyl radical that naturally occurs in the production of oxygen, the cyanobacteria would have had to evolve protective enzymes. But how could natural selection have led the cyanobacteria to evolve these enzymes if the need for them didn’t even exist yet? The explanations are fantasious at best.
Nick Lane describes the dilemma in the book Oxygen, the molecule that made the world:
Before cells could commit to oxygenic photosynthesis, they must have learnt to deal with its toxic waste, or they would surely have been killed, as modern anaerobes are today. But how could they adapt to oxygen if they were not yet producing it? An oxygen holocaust, followed by the emergence of a new world order, is the obvious answer; but we have seen that there is no geological evidence to favour such a catastrophic history. In terms of the traditional account of life on our planet, the difficulty and investment required to split water and produce oxygen is a Darwinian paradox.
If there was a reduced atmosphere without oxygen some time back in the past ( which is btw quite controversial ) then there would be no ozone layer, and if there was no ozone layer the ultraviolet radiation would penetrate the atmosphere and would destroy the amino acids as soon as they were formed. If the Cyanobacterias however would overcome that problem ( its supposed the bacterias in the early earth lived in the water, but that would draw other unsurmountable problems ), and evolve photosynthesis, they would have to evolve at the same time protective enzymes that prevented them oxygen to damage their DNA through hydroxyl radicals. So what evolutionary advantage would there be they to do this ?
Cyanobacteria are the prerequisite for complex life forms. They are said to exist already 3,5 bio years, and did not change morphologically. They do oxygenic photosynthesis, where the energy of light is used to split water molecules into oxygen, protons, and electrons. It occurs in two stages. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide.
They have ATP synthase nano-motors. How could ATP synthase “evolve” from something that needs ATP, manufactured by ATP synthase, to function? Absurd “chicken-egg” paradox!
ATP Synthase is a molecular machine found in every living organisms. It serves as a miniature power-generator, producing an energy-carrying molecule, adenosine triphosphate, or ATP. The ATP synthase machine has many parts we recognize from human-designed technology, including a rotor, a stator, a camshaft or driveshaft, and other basic components of a rotary engine. This machine is just the final step in a long and complex metabolic pathway involving numerous enzymes and other molecules—all so the cell can produce ATP to power biochemical reactions, and provide energy for other molecular machines in the cell. Each of the human body’s 14 trillion cells performs this reaction about a million times per minute. Over half a body weight of ATP is made and consumed every day!
A rotary molecular motor that can work at near 100% efficiency.
We found that the maximum work performed by F1-ATPase per 120° step is nearly equal to the thermodynamical maximum work that can be extracted from a single ATP hydrolysis under a broad range of conditions. Our results suggested a 100% free-energy transduction efficiency and a tight mechanochemical coupling of F1-ATPase.
How could ATP synthase “evolve” from something that needs ATP, manufactured by ATP synthase, to function? Absurd “chicken-egg” paradox! Also, consider that ATP synthase is made by processes that all need ATP—such as the unwinding of the DNA helix with helicase to allow transcription and then translation of the coded information into the proteins that make up ATP synthase. And manufacture of the 100 enzymes/machines needed to achieve this needs ATP! And making the membranes in which ATP synthase sits needs ATP, but without the membranes it would not work. This is a really vicious circle for evolutionists to explain.
They have aerobic respiration, and anaerobic fermentation which uniquely occur together in these prokaryotic cells. They do photosynthesis through complex Photosystem I and II and other electron transport complexes. They have a carbon concentration mechanism, which increases the concentration of carbon dioxide available to the initial carboxylase of the Calvin cycle, the enzyme RuBisCO, and transcriptional regulation, which is the change in gene expression levels by altering transcription rates. They are capable of performing the process of water-oxidizing photosynthesis by coupling the activity of photosystem II and I, in a chain of events known as the Z-scheme. They metabolize Carbohydrates through the pentose phosphate pathway. They reduce Carbon dioxide to form carbohydrates through the Calvin cycle. Furthermore, they are able to reduce elemental sulfur by anaerobic respiration in the dark.
No nitrogen: no proteins, no enzymes, no life. We need nitrogen in our bodies, to form amino acids and nucleic acids. Cyanobacteria have the greatest contribution to nitrogen fixation. So in the beginning, not only was lack of oxygen a gigantic problem, but the lack of nitrogen was no less so. In order for the anaerobic organisms, whatever they might have been, to generate oxygen in quantity, they simply HAD to have nitrogen in their tissues (as enzymes etc). With nitrogen as unreactive as it is, then how did they fix it? N2 gas is a very stable compound due to the strength of the triple bond between the nitrogen atoms, and it requires a large amount of energy to break this bond. This is one of the hardest chemical bonds of all to break.The whole process requires eight electrons and at least sixteen ATP molecules. The process, nitrogenase, works in a more exact and efficient way than the clumsy chemical processes of human invention. Several atoms of iron and molybdenum are held in an organic lattice to form the active chemical site. With assistance from an energy source (ATP) and a powerful and specific complementary reducing agent (ferredoxin), nitrogen molecules are bound and cleaved with surgical precision. In this way, a ‘molecular sledgehammer’ is applied to the NN bond, and a single nitrogen molecule yields two molecules of ammonia. The ammonia then ascends the ‘food chain’, and is used as amino groups in protein synthesis for plants and animals. This is a very tiny mechanism, but multiplied on a large scale it is of critical importance in allowing plant growth and food production on our planet to continue.
They are able to capture the energy of light with 95% efficiency. Recently it has been discovered, that they accomplish that through sophisticated quantum mechanics – an esoteric aspect of nature that even most scientists don’t understand. The use light harvesting antennas for that !!
They possess a autoregulatory transcriptional feedback mechanism called circadian clock and coordinate their activities such as sleep/wake behavior, body temperature, hormone secretion, and metabolism into daily cycles . This is a intrinsic time-keeping mechanism that controls the daily rhythms of numerous physiological processes. They control the expression of numerous genes, including those that code for the oscillator proteins of the clock itself.Cyanobacterias have 1,054 protein families !!!
In a BBC report , they said : Oxygenic photosynthesis is a very complicated metabolism and it makes sense that the evolution of such a metabolism would take perhaps two billion years.
Feel free to explain how Cyanobacteria got these amazing capabilites, amongst others, in a relatively short evolutionary time scale ?
Adventures with cyanobacteria: a personal perspective
Contradictory Phylogenies for Cyanobacteria
The Biogeochemical Cycles of Trace Metals in the Oceans
Genomes of Stigonematalean Cyanobacteria (Subsection V) and the Evolution of Oxygenic Photosynthesis from Prokaryotes to Plastids
Light-driven oxygen production from superoxide by Mn-binding bacterial reaction centers
Biologie Uni Hamburg - Cyanobacteria
Cronodon Cyanobacteria , great !
Some Cyanobacteria adjust their buoyancy by means of gas vacuoles, enabling them to adjust their position in the water column, floating near the surface during the day for photosynthesis and sinking deeper at night to harvest nutrients. Nitrogen fixation requires anaerobic conditions, but Cyanobacteria are aerobes. They solve this problem by having specialized cells called heterocysts which have thick walls impermeable to oxygen and in which nitrogen fixation can occur. Smart, huh?
By producing oxygen as a gas as a by-product of photosynthesis, cyanobacteria are thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of oxygen-intolerant organisms. According to endosymbiotic theory, the chloroplasts found in plants and eukaryotic algae evolved from cyanobacterial ancestors via endosymbiosis.
The Cyanobacteria: Molecular Biology, Genomics, and Evolution
Cyanobacteria are a fascinating and versatile group of bacteria of immense biological importance. Thought to be amongst the first organisms to colonize the earth, these bacteria are the photosynthetic ancestors of chloroplasts in eukaryotes, such as plants and algae. In addition, they can fix nitrogen, survive in very hostile environments (e.g. down to -60-degreesC), are symbiotic, have circadian rhythms, exhibit gliding mobility, and can differentiate into specialized cell types called heterocysts. This makes them ideal model systems for studying fundamental processes, such as nitrogen fixation and photosynthesis. In addition, cyanobacteria produce an array of bioactive compounds, some of which could become novel anti-microbial agents, anti-cancer drugs, UV protectants, etc. The amazing versatility of cyanobacteria has attracted huge scientific interest in recent years. Given that 24 genomes sequences have been completed and many more projects are currently underway, the point has been reached where there is an urgent need to summarize and review the current molecular biology, genomics, and evolution of these important organisms. This volume brings together the expertise and enthusiasm of an international panel of leading cyanobacterial researchers to provide a state-of-the art overview of the field. Topics covered include: evolution, comparative genomics, gene transfer, molecular ecology and environmental genomics, stress responses, bioactive compounds, circadian clock, structure of the photosynthetic apparatus, membrane systems, carbon acquisition, nitrogen assimilation, C/N balance sensing, and much more. This book will be essential for anyone with an interest in cyanobacteria, bacterial photosynthesis, bacterial nitrogen fixation, and symbiosis.
The Molecular Biology of Cyanobacteria summarizes more than a decade of progress in analyzing the taxonomy, biochemistry, physiology, cellular differentiation and developmental biology of cyanobacteria by modern molecular methods, especially molecular genetics. During this period cyanobacterial molecular biologists have been "studying those things that cyanobacteria do well," and they have made cyanobacteria the organisms of choice for detailed molecular analyses of oxygenic photosynthesis. Part 1 contains chapters describing the molecular evolution and taxonomy of the cyanobacteria as well as chapters describing cyanelles and the origins of algal and higher plant chloroplasts. Also included are chapters describing the picoplanktonic, oceanic cyanobacteria and prochlorophytes, "the other cyanobacteria." Part 2 is devoted to a detailed description of structural and functional aspects of the cyanobacterial photosynthetic apparatus. Included are chapters on thylakoid membrane organization, phycobiliproteins, and phycobilisomes, Photosystem I, Photosystem II, the cytochrome b6f complex, ATP synthase, and soluble electron carriers associated with photosynthetic electron transport. Structure as it relates to biological function, is heavily emphasized in this portion of the book. Part 3 describes other important biochemical processes, including respiration, carbon metabolism, inorganic carbon uptake and concentration, nitrogen metabolism, tetrapyrrole biosynthesis, and carotenoid biosynthesis. Part 4 describes the cyanobacterial genetic systems and gene regulatory phenomena in these organisms. Emphasis is placed on responses to environmental stimuli, such as light intensity, light wavelength, temperature, and nutrient availability. Cellular differentiation and development phenomena, including the formation of heterocysts for nitrogen fixation and hormogonia for dispersal of organisms in the environment, are described
Cyanobacteria are moss-like species that live in oxygen-poor environments bathed in light, such as in shallow bodies of water. They are the only bacteria that produce oxygen as a waste product07 -- which is an important task of this early life. They are exceedingly complex, far from what one would think to call primitive. They grow in long chains because when the cells reproduce they divide in half and tend to remain attached (Figure 2b). They secrete a kind of mucilage or slime which solidifies to form characteristic multi-layered dome-like structures called stromatolytes that grow in highly saline tidal basins -- shallow water between high and low tide. Living stromatolytes exist today in only a few locations worldwide, one being Hamelin Pool in Western Australia
If these fossils are cyanobacteria (or closely related ancestors), then it immediately poses a problem because -- as we will see -- cyanobacteia are advanced bacteria, not what one would assume to be representative of the earliest living species
Why bacteria and not archaea?
Some paleo-biologists insist that the earliest life was from the kingdom Archaea (indeed the name implies that they are the most ancient bacteria), based on the ability of archaea to manage in very hostile environments (which the early earth certainly was), and the claimed advantages of survival near deep water thermal vents.
It is not the purpose here to confirm or deny this possibility, but there are some good reasons to doubt that archaea could "be fruitful and multiply and fill the earth" [Gen. 1] to the degree required at this point in the earth's history: Archaea are too limited and specialized to fill that role. In addition, the genetic make-up of the archaea appears to be more advanced than that of bacteria, more akin to eukaryotes, and therefore (one would assume) a later development.
In the final analysis, though, it does not really matter whether the first living species were archaea; the first practical living species had to be bacteria -- oxygen-producing cyanobacteria (or close ancestors) -- and as a matter of fact, these were the first fossils preserved in the fossil record.
From the point of view that the main task of early life was to form a fit place for later life, it is significant that no known archaea species conduct photosynthesis or have oxygen as a waste product, and so they would be unable to convert the initial reducing environment to an oxidizing environment, required for advanced life.
Regarding the appearance of the first life, Alexandre Meinesz, How Life Began: Evolution's Three Geneses refers to "the strange fact that the ancestral bacteria were already highly diversified" when the first fossil evidence was found. He then continues, "The currently popular idea that life probably arose in warm subsurface waters along a mid-ocean ridge, the kind of environment where a great variety of heat-resisting bacteria thrive today, is a hypothesis without any scientific basis."
Could the oxygen and nitrogen cicle be explained by naturalistic means ? The reason for the abundance of oxygen in the atmosphere is the presence of a very large number of organisms which produce oxygen as a byproduct of their metabolism. Cyanobacteria or blue-green algae became the first microbes to produce oxygen by photosynthesis. They are one of the oldest bacteria that live on earth, said to exist perhaps as long as 3.5 billion years. And their capabilities are nothing more than astounding.
No cianobacteria, not enough oxygen, no higher life forms. These cianobacterias have incredibly sophisticated enzyme proteins and metabolic pathways, like the Z-scheme and electron transport chains, ATP synthase motors, circadian clock, the photosynthetic light reactions, carbon concentration mechanism, and transcriptional regulation , they produce binded nitrogen through nitrogenase, a highly sophisticated mechanism to bind nitrogen, used as a nutrient for plant and animal growth. The Nitrogen cycle is a lot more complex than the carbon cycle. Nitrogen is a very important element. It makes up almost 80% of our atmosphere, and it is an important component of proteins and DNA, both of which are the building blocks of animals and plants. Therefore without nitrogen we would lose one of the most important elements on this planet, along with oxygen, hydrogen and carbon. There are a number of stages to the nitrogen cycle, which involve breaking down and building up nitrogen and it’s various compounds.There is no real starting point for the nitrogen cycle. It is an endless cycle. Potential gaps in the system cannot be reasonably bypassed by inorganic nature alone.
It must have a degree of specificity that in all probability could not have been produced by chance. A given function or step in the system may be found in several different unrelated organisms. The removal of any one of the individual biological steps will resort in the loss of function of the system. The data suggest that the nitrogen cycle may be irreducibly interdependent based on the above criteria. No proposed neo-Darwinian mechanisms can explain the origin of such a system.The ultimate source of nitrogen for the biosynthesis of amino acids is atmospheric nitrogen (N2), a nearly inert gas. Its needed by all living things to build proteins and nucleic acids. This is one of the hardest chemical bonds of all to break. So, how can nitrogen be brought out of its tremendous reserves in the atmosphere and into a state where it can be used by living things?
To be metabolically useful, atmospheric nitrogen must be reduced. It must be converted to a useful form. Without "fixed" nitrogen, plants, and therefore animals, could not exist as we know them. This process, known as nitrogen fixation, occurs through lightening, but most in certain types of bacteria, namely cianobacteria. Even though nitrogen is one of the most prominent chemical elements in living systems, N2 is almost unreactive (and very stable) because of its triple bond (N?N). This bond is extremely difficult to break because the three chemical bonds need to be separated and bonded to different compounds. Nitrogenase is the only family of enzymes capable of breaking this bond (i.e., it carries out nitrogen fixation). Nitrogenase is a very complex enzyme system. Nitrogenase genes are distributed throughout the prokaryotic kingdom, including representatives of the Archaea as well as the Eubacteria and Cyanobacteria.With assistance from an energy source (ATP) and a powerful and specific complementary reducing agent (ferredoxin), nitrogen molecules are bound and cleaved with surgical precision.
In this way, a ‘molecular sledgehammer’ is applied to the NN bond, and a single nitrogen molecule yields two molecules of ammonia. The ammonia then ascends the ‘food chain’, and is used as amino groups in protein synthesis for plants and animals. This is a very tiny mechanism, but multiplied on a large scale it is of critical importance in allowing plant growth and food production on our planet to continue. ‘Nature is really good at it (nitrogen-splitting), so good in fact that we've had difficulty in copying chemically the essence of what bacteria do so well.’
If one merely substitutes the name of God for the word 'nature', the real picture emerges.These proteins use a collection of metal ions as the electron carriers that are responsible for the reduction of N2 to NH3. All organisms can then use this reduced nitrogen (NH3) to make amino acids. In humans, reduced nitrogen enters the physiological system in dietary sources containing amino acids. One thing is certain—that matter obeying existing laws of chemistry could not have created, on its own, such a masterpiece of chemical engineering.Without cyanobacteria - no fixed nitrogen is available.Without fixed nitrogen, no DNA, no amino-acids, no protein can be synthesised. Without DNA, no amino-acids,protein, or cyanobacteria are possible. So thats a interdependent system.
This time span was once considered too short for the emergence of something as complex as a living cell. Therefore, a number of people suggested that germs of life may have come to earth from outer space with cometary dust or even via a space probe sent out by some distant civilization.
A phylogenetic analysis based on protein data demonstrates a possibility of six classes of the linker family in cyanobacteria. Emergence, divergence, and disappearance of PBSs linkers among cyanobacterial species were due to speciation, gene duplication, gene transfer, or gene loss, and acclimation to various environmental selective pressures especially light.
Where is the demonstration ??
The origin of multicellularity in cyanobacteria
This publication is unique among a number of books on cyanobacteria because it focuses on the bioenergetics of these widespread organisms which are the evolutionary prerequisite for the development of all higher forms of life on our "blue" planet. The book primarily addresses questions of energy conversion by the fundamental bioenergetic processes: (oxygenic) photosynthesis, (aerobic) respiration, and (anaerobic) fermentation which uniquely occur together in these prokaryotic cells. Thermophilic cyanobacteria offer the most suitable material for high resolution structure analyses of Photosystem I and II and other electron transport complexes by X-ray crystallography (for example, at present the structure of Photosystem II at atomic resolution is only known for these organisms). These achievements during the last decade represent a milestone in our understanding of the complexes which are crucial for solar energy exploitation through photosynthetic water splitting. The present work represents an ambitious attempt to achieve the goal of a synoptic state-of-the-art picture by casting together the mosaics of detailed knowledge described by leading experts in the field.
Cyanobacteria represent one of the most morphologically diverse groups of prokaryotic organisms (Bacteria and Archaea).
Without the cyanobacteria life on this planet would not have started, and would certainly not be continuing to exist.
know that there has been a long-standing consensus on how the oxygen was actually produced: photosynthetic organisms called cyanobacteria
The cyanobacteria have an extensive fossil record. The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old!
Cyanobacteria are among the easiest microfossils to recognize. Morphologies in the group have remained much the same for billions of years, and they may leave chemical fossils behind as well, in the form of breakdown products from pigments. Small fossilized cyanobacteria have been extracted from Precambrian rock, and studied through the use of SEM and TEM (scanning and transmission electron microscopy).
cianobacteria are fully developed eukaryotic cells *supposed* to live since the most early ages, said to be 3,5bio years.
Cyanobacteria are one of the oldest and morphologically most diverse prokaryotic phyla on our planet. The early development of an oxygen-containing atmosphere approximately 2.45 - 2.22 billion years ago is attributed to the photosynthetic activity of cyanobacteria.
During Earth history, cyanobacteria have raised atmospheric oxygen levels starting approximately 2.45 - 2.22 billion years ago and provided the basis for the evolution of aerobic respiration
what a nice *accident*, isnt it ? why is it supposed to be rational, to evoke good luck or unsupported natural selection to explain such a event , that was necessary for complex life to arise ?
The latter have the ability to produce heterocysts for nitrogen fixation and akinetes (climate-resistant resting cells).
my question made previously, *of course* , remains unanswered :
How could those regulatory machines evolve at precisely the right rate so as to drop into the right place at precisely the right time to effect proper assembly of the nitrogenase machinery?
Unquestionably, biological nitrogen fixation is no simple process and
a design argument could be made based on this single step in the nitrogen
cycle. It is unlikely to have been produced via a step-by-step Darwinian
process because nitrogenase itself is immensely complex, requires auxiliary
complex mechanisms to maintain low oxygen tension, and also needs
reduced carbon backbones as substrates for amination to store ammonia
as glutamine. In addition, regulatory mechanisms are needed to coordinate
the entire energetically expensive activity and its chemically reactive
Prochlorococcus is a genus of very small (0.6 µm) marine cyanobacteria with an unusual pigmentation (chlorophyll b). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth. Microbes of the genus Prochlorococcus are among the major primary producers in the ocean, responsible for at least 50% of atmospheric oxygen. Analysis of the genome sequences of 12 Prochlorococcus strains show that 1100 genes are common to all strains, and the average genome size is about 2000 genes. In contrast, eukaryotic algae have over 10,000 genes
Preparation for advanced life. The rapid multiplication of the early species of life was needed to prepare the earth for more advanced species. Almost three billion years separate the first fossils and the first eukaryotic fossils -- the first step towards complex, multicellular life.
Looking ahead, the main tasks for the early bacteria were:
• Distribute abundant amounts of organic food worldwide.
- This task is needed because advanced life cannot take the time or energy to be self-sufficient (autotrophic).
- In particular, this food provides fixed nitrogen, which is essential for all of life. Its manufacture from atmospheric nitrogen is a difficult, energy-consuming slow process (see below). No eukaryotic species is able to manufacture nitrogen. In fact, very few bacteria species are able to manufacture all of its own requirements for nitrogen. The nitrogen may be either organic or inorganic (in the form of nitrates or ammonia gas).
• Convert the earth's atmosphere and the oceans from reducing to oxidizing. The atmosphere must have around 20-25% oxygen content. Complex life requires at least the lower limit of abundance, and the upper bound is needed to avoid spontaneous combustion.
It appears that the limiting requirement was the oxygen supply, which took the full three billion years to achieve, with the aid of oxygen-producing bacteria. The global distribution of the food supply, fixed nitrogen, and the formation of vast mineral deposits that are so essential to the modern technological age were by-products of this push to develop the oxygen supply.
The cyanobacterial genome core and the origin of photosynthesis
Cyanobacteria are one of the earliest branching groups of organisms on this planet (1, 2). They are the only known prokaryotes to carry out oxygenic photosynthesis, and there is little doubt that they played a key role in the formation of atmospheric oxygen ≈2.3 Gyr ago (2). Despite its evolutionary, environmental, and geochemical importance, many aspects of cyanobacterial cell life remain obscure (3–5). Genome sequencing opened a new chapter in cyanobacterial research. In the last few years, complete genome sequences of several freshwater and marine cyanobacteria became available, providing ample data for systematic analysis. A comparison of the complete genomes from three different strains of Prochlorococcus spp. demonstrated a wide variety of gene complements within this genus due to massive genome reduction in some lineages (6, 7). Studies of the genes shared by cyanobacteria and other photosynthetic organisms allowed delineation of the “photosynthetic gene set” and demonstrated a significant extent of lateral gene transfer (LGT) among phototrophic bacteria (8–11). A somewhat surprising result of the latter work has been that genes for most proteins involved in photosynthesis (hereafter “photosynthetic genes”) were not in the photosynthetic gene set.
We compared proteins encoded in 15 complete cyanobacterial genomes, including five genomes of Prochlorococcus spp., to define the minimal set of genes common to all cyanobacteria and to trace the conservation of these genes among other taxa. We analyzed the phylogenetic affinities of genes in this set and identified previously unrecognized candidate photosynthetic genes. We further used this gene set to address the identity of the first phototrophs, a subject of intense discussion in recent years (8, 9, 12–33). We show that cyanobacteria and plants share numerous photosynthesis-related genes that are missing in genomes of other phototrophs. This observation suggests, in agreement with geological evidence, that (now extinct) anoxygenic ancestors of cyanobacteria are the most plausible candidates for the ancestral photoautotrophs, which apparently disseminated parts of their photosynthetic apparatus to other bacteria by way of LGT.
Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods?
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