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Nowadays, cyanobacteria are regarded as promising "low-cost" microbial cell factories for carbon capture and storage, and for the sustainable production of secondary metabolites and biofuels, thanks to their simple nutritional requirements, their metabolic plasticity, and the powerful genetics of some model strains.
In agreement with cyanobacteria being regarded as the ancestor of the chloroplast, the stromal portion of the chloroplast division complex resemble the cyanobacterial cell division machinery, but many other components were lost after the endosymbiotic event. Cyanobacteria are prokaryotes with cell envelopes typical for Gram-negative bacteria.
The cell envelope consists of four distinct layers, the plasma membrane, the peptidoglycan layer, the outer membrane and in some cases the surface or S-layer.
Often, the latter three are referred to as the cell wall. The functionality of the cell envelope is defined by the cooperative action of lipids and membrane-embedded proteins.
The membranes of cyanobacterial species contain two types of lipids, phosphoglycerolipids and galactolipids. The proteins perform many distinct functions ranging from solute transport to signal transduction. Thus, several features are indeed comparable between the cyanobacterial and the proteobacterial systems investigated so far. However, some properties are unique for the cyanobacterial branch.
In this chapter, we summarize the current knowledge on composition, structure and function of the cell envelope including information obtained from different cyanobacterial strains.
We also compare the properties of the cyanobacterial envelope to those of non-photosynthetic Gram-negative bacteria. Oxygenic photosynthesis evolved in the thylakoid membrane of ancient cyanobacteria.
Here we review, from the proteomics viewpoint, the composition and biogenesis of the present day cyanobacteria thylakoid membranes, with main emphasis on the macromolecular protein complexes involved in photosynthetic electron transfer. Response of the thylakoid membrane proteome to changes in environmental cues and to various stress conditions is also described and discussed in terms of dynamic modifications in metabolic and catabolic pathways in order to adjust cyanobacterial cells to a new environment.
Protein Targeting, Transport and Translocation in Cyanobacteria. In contrast to other bacteria, cyanobacterial cells are composed of six different subcellular compartments, and proteins might be localized in one of the three membrane systems outer, cytoplasmic or thylakoid membrane or within one of the three soluble compartments, i. As cyanobacterial cells appear to have distinct sets of proteins localized only in a single subcellular compartment, these organisms eventually have evolved mechanisms to localize proteins to specific membranes for membrane integration or for translocation across these membranes.
In the present article we summarize findings on the membrane structure of cyanobacterial cells as well as on heterogeneous protein distribution, and we discuss current models aiming at explaining mechanisms involved in protein targeting and sorting in cyanobacteria. Our understanding of chromatic acclimation, during which the light harvesting antennae or phycobilisomes of cyanobacteria are modified to optimized to maximize photon capture for photosynthesis, has grown remarkably over the past century.
Originally a curiosity of a "chameleon cyanobacteria" capable of dramatically altering its pigmentation between red and green in response to changes in the ambient light color, multiple forms of chromatic acclimation are now known to exist and are found in a wide range of species in most habitats on Earth. This ecologically important process gives species that possess it a fitness advantage in environments with fluctuating light color conditions.
The form of chromatic acclimation found in deeper marine environments is sensitive to blue and green light and involves the selective substitution of light-absorbing chromophores for these specific wavelengths, while other types of chromatic acclimation are maximally sensitive to the green and red regions of the visible spectrum and involve the reversible replacement of both proteins and chromophores within the phycobilisomes as well as changes in many other cellular processes.
Although some progress has been made in unraveling the mechanisms by which these organisms sense and respond to changes in light color conditions, many questions remain to be answered. The ability to use light energy for the accumulation and fixation of CO 2 has given cyanobacteria the ability to thrive in diverse and extreme environments.
Cyanobacteria play a central role in the global carbon cycle and have changed the earth's atmosphere by generating oxygen and depleting CO 2.
The CO 2 concentrating mechanism CCM consists of active transport systems for inorganic carbon acquisition and a distinctive protein-based organelle, the carboxysome.
Recent advances in structural and systems biology and biological imaging have built upon decades of biochemical and genetic research to advance our understanding of the carboxysome. In this chapter we provide an overview of the carboxysome structure and place the carboxysome in the context of cyanobacterial metabolism and morphology.
All microorganisms accumulate carbon and energy reserves to cope with starvation conditions temporally present in the environment. In cyanobacteria, glycogen biosynthesis is the main strategy for metabolic sink and storage of photosynthetically fixed carbon. Glycogen biosynthesis is therefore tightly coupled to light and dark reactions of photosynthesis.
Inversely, the process of glycogen degradation provides carbon and energy for adverse cellular processes. Cyanophycin: a Cellular Nitrogen Reserve Material. Cyanophycin is a biopolymer that serves as a nitrogen cellular reserve and occurs in most, albeit not all cyanobacteria.
In most forms the photosynthetic machinery is embedded into folds of the cell membrane, called thylakoids. Because of their ability to fix nitrogen in aerobic conditions they are often found in symbiontic partnerships with a number of other groups of organisms, including but not limited to fungi lichens , corals, pteridophytes Azolla , and angiosperms Gunnera. Many cyanobacteria are able to reduce ambient levels of nitrogen and carbon dioxide under aerobic conditions, a fact that may be responsible for their evolutionary and ecological success.
In anaerobic conditions, they are also able to use only PS I—cyclic photophosphorylation—with electron donors other than water for example hydrogen sulfide , in the same way as the purple photosynthetic bacteria.
They also share an archaeal property, the ability to reduce elemental sulfur by anaerobic respiration in the dark. Their photosynthetic electron transport shares the same compartment as the components of respiratory electron transport. Their plasma membrane contains only components of the respiratory chain, while the thylakoid membrane hosts both respiratory and photosynthetic electron transport.
The cyanobacteria were traditionally classified by morphology into five sections, referred to by the numerals I-V. The first three—Chroococcales, Pleurocapsales, and Oscillatoriales—are not supported by phylogenetic studies.
However, the latter two—Nostocales and Stigonematales—are monophyletic, and make up the heterocystous cyanobacteria. Some cyanobacteria produce toxins, called cyanotoxins. This results in algal blooms, which can become harmful to other species including humans if the cyanobacteria involved produce toxins.
Learning Objectives Describe the characteristics associated with Cyanobacteria including: cell types, forms of motility and metabolic properties Explain the following laws within the Ideal Gas Law. Some filamentous colonies show the ability to differentiate into several different cell types, including: Vegetative cells, the normal, photosynthetic cells that are formed under favorable growing conditions.
Akinetes, the climate-resistant spores that may form when environmental conditions become harsh. Thick-walled heterocysts, which contain the enzyme nitrogenase, vital for nitrogen fixation.
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