Prokaryotic Cell Architecture(Bacteria) Structurally, a Bacterial Cell

Total Page:16

File Type:pdf, Size:1020Kb

Prokaryotic Cell Architecture(Bacteria) Structurally, a Bacterial Cell Prokaryotic Cell Architecture(bacteria) Structurally, a bacterial cell (Figure below) has three architectural regions: appendages (attachments to the cell surface) in the form of flagella and pili (or fimbriae); a cell envelope consisting of a capsule, cell wall and plasma membrane; and a cytoplasmic region that contains the cell chromosome (DNA) and ribosomes and various sorts of inclusions. Schematic drawing of a typical bacterial cell. Appendages Flagella Flagella are filamentous protein structures attached to the cell surface that provide the swimming movement for most motile prokaryotes. The diameter of a procaryotic flagellum is about 20 nanometers, well-below the resolving power of the light microscope. The flagellar filament is rotated by a motor apparatus in the plasma membrane allowing the cell to swim in fluid environments. Bacterial flagella are powered by proton motive force (chemiosmotic potential) established on the bacterial membrane, rather than ATP hydrolysis which powers eukaryotic flagella. About half of the bacilli and all of the spiral and curved bacteria are motile by means of flagella. Very few cocci are motile, which reflects their adaptation to dry environments and their lack of hydrodynamic design. Salmonella enterica. The enteric are motile by means of peritrichous flagella. Flagella may be variously distributed over the surface of bacterial cells in distinguishing patterns, but basically flagella are either polar (one or more 1 flagella arising from one or both poles of the cell) or peritrichous (lateral flagella distributed over the entire cell surface). Flagellar distribution is a genetically-distinct trait that is occasionally used to characterize or distinguish bacteria. For example, among Gram-negative rods, pseudomonads have polar flagella to distinguish them from enteric bacteria, which have peritrichous flagella. Fimbriae and Pili Fimbriae and Pili are interchangeable terms used to designate short, hair-like structures on the surfaces of prokaryotic cells. Like flagella, they are composed of protein. Fimbriae are shorter and stiffer than flagella, and slightly smaller in diameter. Generally, fimbriae have nothing to do with bacterial movement (there are exceptions, e.g. twitching movement on Pseudomonas). There are two types of Pili: Common Pili (often called fimbriae) are usually involved in specific adherence (attachment) of prokaryotes to surfaces in nature. In medical situations, they are major determinants of bacterial virulence . The F or sex pilus, mediates DNA transfer during conjugation and apparently stabilizes mating bacteria during the process of conjugation. Gram-positive wall is a uniformly thick layer external to the plasma membrane. It is composed mainly of peptidoglycan (murein). The Gram-negative wall appears thin and multilayered. It consists of a relatively thin peptidoglycan sheet between the plasma membrane and a phospholipid-lipopolysaccharide outer membrane. The space between the inner (plasma) and outer membranes (wherein the peptidoglycan resides) is called the periplasm. Capsules Most bacteria contain some sort of a polysaccharide layer outside of the cell wall polymer. In a general sense, this layer is called a capsule. A true capsule is a discrete detectable layer of polysaccharides deposited outside the cell wall. A less discrete structure or matrix which embeds the cells is a called a slime layer or a biofilm. A type of capsule found in bacteria called a glycocalyx or microcapsule is a very thin layer of tangled polysaccharide fibers on the cell surface. Capsules have several functions and often have multiple functions in a particular organism. Like fimbriae, capsules, slime layers, and glycocalyx often 2 mediate adherence of cells to surfaces. Capsules also protect bacterial cells from engulfment by predatory protozoa or white blood cells (phagocytes), or from attack by antimicrobial agents of plant or animal origin. Capsules in certain soil bacteria protect cells from perennial effects of drying or desiccation. Capsular materials (e.g. dextrans) may be overproduced when bacteria are fed sugars to become reserves of carbohydrate for subsequent metabolism. A classic example of biofilm construction in nature is the formation of dental plaque mediated by the oral bacterium, Streptococcus mutans. The bacteria adhere specifically to the pellicle of the tooth by means of a protein on the cell surface. The bacteria grow and synthesize a dextran capsule which binds them to the enamel and forms a biofilm some 300-500 cells in thickness. The bacteria are able to cleave sucrose (provided by the animal diet) into glucose plus fructose. The fructose is fermented as an energy source for bacterial growth. The glucose is polymerized into an extracellular dextran polymer that cements the bacteria to tooth enamel and becomes the matrix of dental plaque. The dextran slime can be depolymerized to glucose for use as a carbon source, resulting in production of lactic acid within the biofilm (plaque) that decalcifies the enamel and leads to dental caries or bacterial infection of the tooth. Figure 16 (Left) Dental plaque revealed by a harmless red dye. Figure 13. Bacterial capsules outlined by India ink viewed by light microscopy. The Cell Envelope The cell envelope is a descriptive term for the several layers of material that envelope or enclose the protoplasm of the cell. The cell protoplasm (cytoplasm) is surrounded by the plasma membrane, a cell wall and a capsule. The cell wall itself is a layered structure in Gram-negative bacteria. All cells have a plasma membrane, which is the essential and definitive 3 characteristic of a "cell". Almost all prokaryotes have a cell wall to prevent damage to the underlying protoplast. Outside the cell wall, foremost as a surface structure, may be a polysaccharide capsule or glycocalyx. Figure 12. Profiles of the cell envelope the Gram-positive and Gram- negative bacteria. Cell Wall Most prokaryotes have a rigid cell wall. The cell wall is an essential structure that protects the cell protoplast (the region bound by and including the membrane) from mechanical damage and from osmotic rupture or lysis. Bacteria usually live in relatively dilute environments such that the accumulation of solutes inside the cell cytoplasm greatly exceeds the total solute concentration in the outside environment. Thus, the osmotic pressure against the inside of the plasma membrane may be the equivalent of 10-25 atmospheres. Since the membrane is a delicate, plastic structure, it must be restrained by an outside wall made of porous, rigid material that has high tensile strength. Such a material is murein, the ubiquitous component of bacterial cell walls. Bacterial murein is a unique type of peptidoglycan. Peptidoglycan is a polymer of sugars (a glycan) cross-linked by short chains of amino acids (peptide). All bacterial peptidoglycan contain N-acetylmuramic acid, which is the definitive component of murein.The profiles of the cell surface of bacteria, as seen with the electron microscope, are drawn in Figure 12. In Gram-positive Bacteria (those that retain the purple crystal violet dye when subjected to the Gram-staining procedure) the cell wall is thick (15-80 nanometers), consisting of several layers of peptidoglycan. Running perpendicular to the peptidoglycan sheets are a group of molecules called teichoic acids which are unique to the Gram-positive cell wall. Peptidoglycan is a polysaccharide consisting of alternating amino sugars (N-acetylglucosamine (NAG) and N- acetyl muramic acid (NAM)) linked by Beta 1-4 bonds like those in cellulose. The Beta 1-4 bond can be broken by an enzyme called lysozyme that is present in your tears, saliva, blood, other bodily fluids and egg white. These polysaccharide chains are held together by peptide cross-links . These peptides that they may contain D-amino acids. 4 Antibiotics like penicillin and cephalosporin inhibit the enzymes that synthetise peptidoglycan. This is why these antibiotics are not affective against the eucaryotic cells of fungi and parsites. Figure 17. Structure of the Gram-positive bacterial cell wall. The wall is relatively thick and consists of many layers of peptidoglycan interspersed with teichoic acids that run perpendicular to the peptidoglycan sheets. In the Gram-negative Bacteria (which do not retain the crystal violet in the Gram-stain procedure) the cell wall is relatively thin (10 nanometers) and is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane. The outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS or endotoxin), which is toxic to animals. In Gram-negative bacteria the outer membrane is usually considered as part of the cell wall. Figure 18. Structure of the Gram-negative cell wall. The wall is relatively thin and contains much less peptidoglycan than the Gram-positive wall. Also, teichoic acids are absent. However, the Gram negative cell wall consists of an outer membrane that is outside of the peptidoglycan layer. The outer membrane is attached to the peptidoglycan sheet by a unique group of lipoprotein molecules. Of special interest as a component of the Gram-negative cell wall is the outer membrane, a discrete bilayered structure on the outside of the peptidoglycan 5 sheet (see Figure 12 above and Figure 19 below). For the bacterium, the outer membrane is first and foremost a permeability barrier, but primarily due to its lipopolysaccharide content, it possesses many interesting
Recommended publications
  • Prokaryotes (Domains Bacteria & Archaea)
    2/4/15 Prokaryotes (Domains Bacteria & Archaea) KEY POINTS 1. Decomposers: recycle organic and inorganic molecules in environment; makes them available to other organisms. 2. Essential components of symbioses. 3. Encompasses the origins of metabolism and metabolic diversity. 4. Origin of photosynthesis and formation of atmospheric Oxygen Ceno- Meso- zoic zoic ANTIQUITY Humans Paleozoic Colonization of land Animals Origin of solar system and Earth • >3.5 BILLION years old. • Alone for 2 1 4 billion years Proterozoic Archaean Prokaryotes Billions of 2 years ago3 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen General characteristics 1. Small: compare to 10-100µm for 0.5-5µm eukaryotic cell; single-celled; may form colonies. 2. Lack membrane- enclosed organelles. 3. Cell wall present, but different from plant cell wall. 1 2/4/15 General characteristics 4. Occur everywhere, most numerous organisms. – More individuals in a handful of soil then there are people that have ever lived. – By far more individuals in our gut than eukaryotic cells that are actually us. General characteristics 5. Metabolic diversity established nutritional modes of eukaryotes. General characteristics 6. Important decomposers and recyclers 2 2/4/15 General characteristics 6. Important decomposers and recyclers • Form the basis of global nutrient cycles. General characteristics 7. Symbionts!!!!!!! • Parasites • Pathogenic organisms. • About 1/2 of all human diseases are caused by Bacteria General characteristics 7. Symbionts!!!!!!! • Parasites • Pathogenic organisms. • Extremely important in agriculture as well. Pierce’s disease is caused by Xylella fastidiosa, a Gamma Proteobacteria. It causes over $56 million in damage annually in California. That’s with $34 million spent to control it! = $90 million in California alone.
    [Show full text]
  • The First Cells Were Most Likely Very Simple Prokaryotic Forms. Ra- Spirochetes
    T HE O RIGIN OF E UKARYOTIC C ELLS The first cells were most likely very simple prokaryotic forms. Ra- spirochetes. Ingestion of prokaryotes that resembled present-day diometric dating indicates that the earth is 4 to 5 billion years old cyanobacteria could have led to the endosymbiotic development of and that prokaryotes may have arisen more than 3.5 billion years chloroplasts in plants. ago. Eukaryotes are thought to have first appeared about 1.5 billion Another hypothesis for the evolution of eukaryotic cells proposes years ago. that the prokaryotic cell membrane invaginated (folded inward) to en- The eukaryotic cell might have evolved when a large anaerobic close copies of its genetic material (figure 1b). This invagination re- (living without oxygen) amoeboid prokaryote ingested small aerobic (liv- sulted in the formation of several double-membrane-bound entities ing with oxygen) bacteria and stabilized them instead of digesting them. (organelles) in a single cell. These entities could then have evolved This idea is known as the endosymbiont hypothesis (figure 1a) and into the eukaryotic mitochondrion, nucleus, and chloroplasts. was first proposed by Lynn Margulis, a biologist at Boston Univer- Although the exact mechanism for the evolution of the eu- sity. (Symbiosis is an intimate association between two organisms karyotic cell will never be known with certainty, the emergence of of different species.) According to this hypothesis, the aerobic bac- the eukaryotic cell led to a dramatic increase in the complexity and teria developed into mitochondria, which are the sites of aerobic diversity of life-forms on the earth. At first, these newly formed eu- respiration and most energy conversion in eukaryotic cells.
    [Show full text]
  • Prokaryotes, Protists, Reconstructing the Photosynthesis, Evolution of Living Things
    Prokaryotes, Protists, Reconstructing the Photosynthesis, evolution of living things Endosymbiosis • Systematists study evolutionary relationships Ch 28 & 29 •Look for shared derived (=different from ancestor) traits to group organisms • Evidence used: morphology, 26 February 2009 development, and molecular data (especially DNA sequences) ECOL 182R UofA K. E. Bonine 1 2 Why can’t we figure it out perfectly? • More distant history is obscured by more changes trypanosomes • Among oldest lineages of Bacteria and Archaea in particular, lots of “lateral gene transfer.” Makes it difficult to infer relationships from phylogeny of red blood cells single genes. 3 4 Early prokaryote fossil Diversity of Prokaryotes Bacteria & Archaea 5 6 1 What are microbes? Life can be divided into 3 domains • Only a minority make us sick •Robert Koch, Germ Theory of Disease • In ordinary English, might be anything small 3.8bya –bacteria 1.5bya –yeast –protists – viruses •Prokaryotes = bacteria + archaea • In science, classify by evolutionary • Prokaryote was ancestral and only form for relationships… 7 billions of years 8 Eukarya Scheme has been revised before: Haeckel (1894) Whittaker (1959) Woese (1977) Woese (1990) Three kingdoms Five kingdoms Six kingdoms Three domains Eubacteria Bacteria Monera (prokaryotes) Protista Archaebacteria Archaea Protista Protista Fungi Fungi Plantae Eukarya are Prokaryotes monophyletic, Plantae Plantae Animalia Animalia Animalia paraphyleticparaphyletic, polyphyletic? 9 modified from Wikipedia 10 Shared by all 3 domains Unique to
    [Show full text]
  • Prokaryote Vs. Eukaryote Campaign Biology Name: ______Period: ______
    Prokaryote vs. Eukaryote Campaign Biology Name: ___________________________________________ Period: ____________ Prokaryotes vs. Eukaryotes: A Campaign for Election as Coolest Cell Type! Purpose: While prokaryotes and eukaryotes share some similar structures and characteristics of life, the two lead some pretty different lives! Your job in this assignment is to create a campaign poster and a campaign platform commercial for a prokaryote or a eukaryote as they campaign to be elected coolest cell type! Directions: Each group will be assigned a campaign platform from those listed below. Use the resources listed (as well as any others you might find) to understand why your platform makes your cell type the coolest. Create a campaign poster (using one slide on a Google Presentation, shared between partners, and submitted by due date via a form) and a short campaign platform commercial (given as a speech in class) using the attached rubric. Prokaryotic campaign platforms: 1. Ability to form endospores http://goo.gl/Y1tUK http://goo.gl/DhVNe 2. Ability to form biofilms with other cells http://goo.gl/umy7Z http://goo.gl/m9d5W 3. Quorum sensing neighboring cells http://goo.gl/DSiJU http://goo.gl/IFFtA 4. Production of bacteriocins http://goo.gl/lW75y http://goo.gl/WzFv1 5. Endosymbiotic theory http://goo.gl/6VIba http://goo.gl/uSYh4 Eukaryotic campaign platforms: 6. Contain organelles that have their own genetic material in addition to that found in the nucleus http://goo.gl/6VIba http://goo.gl/Nqesq 7. Vesicles http://goo.gl/bwF3x http://goo.gl/j3qY3 8. Membrane bound organelles that facilitate transport (endomembrane system) http://goo.gl/j3qY3 http://goo.gl/i4brZ 9.
    [Show full text]
  • Cell Structure and Function in the Bacteria and Archaea
    4 Chapter Preview and Key Concepts 4.1 1.1 DiversityThe Beginnings among theof Microbiology Bacteria and Archaea 1.1. •The BacteriaThe are discovery classified of microorganismsinto several Cell Structure wasmajor dependent phyla. on observations made with 2. theThe microscope Archaea are currently classified into two 2. •major phyla.The emergence of experimental 4.2 Cellscience Shapes provided and Arrangements a means to test long held and Function beliefs and resolve controversies 3. Many bacterial cells have a rod, spherical, or 3. MicroInquiryspiral shape and1: Experimentation are organized into and a specific Scientificellular c arrangement. Inquiry in the Bacteria 4.31.2 AnMicroorganisms Overview to Bacterialand Disease and Transmission Archaeal 4.Cell • StructureEarly epidemiology studies suggested how diseases could be spread and 4. Bacterial and archaeal cells are organized at be controlled the cellular and molecular levels. 5. • Resistance to a disease can come and Archaea 4.4 External Cell Structures from exposure to and recovery from a mild 5.form Pili allowof (or cells a very to attach similar) to surfacesdisease or other cells. 1.3 The Classical Golden Age of Microbiology 6. Flagella provide motility. Our planet has always been in the “Age of Bacteria,” ever since the first 6. (1854-1914) 7. A glycocalyx protects against desiccation, fossils—bacteria of course—were entombed in rocks more than 3 billion 7. • The germ theory was based on the attaches cells to surfaces, and helps observations that different microorganisms years ago. On any possible, reasonable criterion, bacteria are—and always pathogens evade the immune system. have been—the dominant forms of life on Earth.
    [Show full text]
  • Cell Theory VOCABULARY Unit 2: Cells Unit 2: > RE B
    3.1 Cell Theory KEY CONCEPT Cells are the basic unit of life. VOCABULARY cell theory MAIN IDEAS cytoplasm Early studies led to the development of the cell theory. organelle Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. prokaryotic cell eukaryotic cell Connect to Your World You and all other organisms are made of cells. As you saw on the previous page, > a cell’s structure is closely related to its function. Today we know that cells are the smallest unit of living matter that can carry out all processes required for life. But before the 1600s, people had many other ideas about the basis of life. Like many breakthroughs, the discovery of cells was aided by the development of new technology—in this case, the microscope. MAIN IDEA Early studies led to the development of the READING TOOLBOX cell theory. TAKING NOTES As you read, make an outline Almost all cells are too small to see without the aid of a microscope. Although using the headings as topics. glass lenses had been used to magnify images for hundreds of years, the early Summarize details that further lenses were not powerful enough to reveal individual cells. The invention of explain those ideas. the compound microscope in the late 1500s was an early step toward this I. Main Idea discovery. The Dutch eyeglass maker Zacharias Janssen, who was probably A. Supporting idea assisted by his father, Hans, usually gets credit for this invention. 1. Detail A compound microscope contains two or more lenses. Total magnification, the 2.
    [Show full text]
  • Structure of Bacterial and Archaeal Cells
    © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 4 CHAPTER PREVIEW 4.1 There Is Tremendous Diversity Structure of Among the Bacteria and Archaea 4.2 Prokaryotes Can Be Distinguished by Their Cell Shape and Arrangements Bacterial and 4.3 An Overview to Bacterial and Archaeal Cell Structure 4.4 External Cell Structures Interact Archaeal Cells with the Environment Investigating the Microbial World 4: Our planet has always been in the “Age of Bacteria,” ever since the The Role of Pili first fossils—bacteria of course—were entombed in rocks more than TexTbook Case 4: An Outbreak of 3 billion years ago. On any possible, reasonable criterion, bacteria Enterobacter cloacae Associated with a Biofilm are—and always have been—the dominant forms of life on Earth. —Paleontologist Stephen J. Gould (1941–2002) 4.5 Most Bacterial and Archaeal Cells Have a Cell Envelope “Double, double toil and trouble; Fire burn, and cauldron bubble” is 4.6 The Cell Cytoplasm Is Packed the refrain repeated several times by the chanting witches in Shakespeare’s with Internal Structures Macbeth (Act IV, Scene 1). This image of a hot, boiling cauldron actu- MiCroinquiry 4: The Prokaryote/ ally describes the environment in which many bacterial, and especially Eukaryote Model archaeal, species happily grow! For example, some species can be iso- lated from hot springs or the hot, acidic mud pits of volcanic vents ( Figure 4.1 ). When the eminent evolutionary biologist and geologist Stephen J. Gould wrote the opening quote of this chapter, he, as well as most micro- biologists at the time, had no idea that embedded in these “bacteria” was another whole domain of organisms.
    [Show full text]
  • Prokaryotes – Bacteria
    Prokaryotes – Bacteria Prokaryotes, which includes, bacteria are the simplest of all the cells. All prokaryotes have a single, circular chromosome and lack a nucleus and membrane-bound organelles. There are two major groups of prokaryotic organisms --- the Kingdom Eubacteria and the Kingdom Archaebacteria. Eubacteria are known as true bacteria. They are the most common type of prokaryote. They are found everywhere, on surfaces and in the soil. Archaebacteria or the ancient bacteria are found in extreme environments, like hot sulfur springs and thermal vents in the ocean floor. They belong to the domain Archaea. Archaebacteria are thought to be some of the oldest life forms on earth. 1.What characteristics do all prokaryotes have in common? 2.What is the best known prokaryote and where can they be found? 3.Name the 2 kingdoms for prokaryotes. 4.Name the 2 bacterial domains. 1 5.Where are the bacterial members of the domain Archaea found? Give an example. 6.What are thought to be the oldest organisms on Earth? Most bacteria are heterotrophic and don't make their own food. That means they have to rely on other organisms to provide them with food. Some bacteria such as the cyanobacteria contain chlorophyll and can make their own food. These bacteria have to break down, or decompose, other living things to obtain energy. Very few bacteria cause illness. Some bacteria are used to make food, such as cheese and yogurt. Scientists have genetically engineered a type of bacteria that breaks down oil from oil spills. Some bacteria like E.coli, live inside the guts of animals and help them to digest food.
    [Show full text]
  • Prokaryotic Growth and Nutrition
    37623_CH05_137_160.pdf 11/11/06 7:23 AM Page 137 © Jones and Bartlett Publishers. NOT FOR SALE OR DISTRIBUTION 5 Chapter Preview and Key Concepts 5.1 Prokaryotic Reproduction Prokaryotic • Binary fission produces genetically-identical daughter cells. • Prokaryotes vary in their generation times. Growth and 5.2 Prokaryotic Growth • Bacterial population growth goes through four phases. • Endospores are dormant structures to endure Nutrition times of nutrient stress. • Growth of prokaryotic populations is sensitive to temperature, oxygen gas, and pH. But who shall dwell in these worlds if they be inhabited? . Are we or 5.3 Culture Media and Growth Measurements • Culture media contain the nutrients needed for they Lords of the World? . optimal prokaryotic growth. —Johannes Kepler (quoted in The Anatomy of Melancholy) • Special chemical formulations can be devised to isolate and identify some prokaryotes. MicroInquiry 5: Identification of Bacterial Species Books have been written about it; movies have been made; even a • Two standard methods are available to produce radio play in 1938 about it frightened thousands of Americans. What pure cultures. is it? Martian life. In 1877 the Italian astronomer, Giovanni Schiapar- • Prokaryotic growth can be measured by direct elli, saw lines on Mars, which he and others assumed were canals built and indirect methods. by intelligent beings. It wasn’t until well into the 20th century that this notion was disproved. Still, when we gaze at the red planet, we won- der: Did life ever exist there? We are not the only ones wondering. Astronomers, geologists, and many other scientists have asked the same question. Today microbiol- ogists have joined their comrades, wondering if microbial life once existed on the Red Planet or, for that matter, elsewhere in our Solar System.
    [Show full text]
  • A Metagenomics Roadmap to the Uncultured Genome Diversity in Hypersaline Soda Lake Sediments Charlotte D
    Vavourakis et al. Microbiome (2018) 6:168 https://doi.org/10.1186/s40168-018-0548-7 RESEARCH Open Access A metagenomics roadmap to the uncultured genome diversity in hypersaline soda lake sediments Charlotte D. Vavourakis1 , Adrian-Stefan Andrei2†, Maliheh Mehrshad2†, Rohit Ghai2, Dimitry Y. Sorokin3,4 and Gerard Muyzer1* Abstract Background: Hypersaline soda lakes are characterized by extreme high soluble carbonate alkalinity. Despite the high pH and salt content, highly diverse microbial communities are known to be present in soda lake brines but the microbiome of soda lake sediments received much less attention of microbiologists. Here, we performed metagenomic sequencing on soda lake sediments to give the first extensive overview of the taxonomic diversity found in these complex, extreme environments and to gain novel physiological insights into the most abundant, uncultured prokaryote lineages. Results: We sequenced five metagenomes obtained from four surface sediments of Siberian soda lakes with a pH 10 and a salt content between 70 and 400 g L−1. The recovered 16S rRNA gene sequences were mostly from Bacteria,evenin the salt-saturated lakes. Most OTUs were assigned to uncultured families. We reconstructed 871 metagenome-assembled genomes (MAGs) spanning more than 45 phyla and discovered the first extremophilic members of the Candidate Phyla Radiation (CPR). Five new species of CPR were among the most dominant community members. Novel dominant lineages were found within previously well-characterized functional groups involved in carbon, sulfur, and nitrogen cycling. Moreover, key enzymes of the Wood-Ljungdahl pathway were encoded within at least four bacterial phyla never previously associated with this ancient anaerobic pathway for carbon fixation and dissimilation, including the Actinobacteria.
    [Show full text]
  • Prokaryotic Cell Features
    Prokaryotic Cell Features Size The small size of prokaryotic cells affects their physiology, growth rate, and ecology. Due to their small cell size, most prokaryotes have the highest surface area–to–volume ratio of any cells. This characteristic aids in nutrient and waste exchange with the environment. As a cell increases in size, its surface area-to-volume ratio decreases For a sphere, S / V = 3/r Prokaryotes maintain a high surface area to volume ratio by their smallness. 1. TRANSPORT RATE: Efficient transport of raw materials in and wastes out 2. GROWTH RATE: Nutrient exchange limits growth rates. Many prokaryotes = high metabolic activity (fast growth, reproductive rate). 3. EVOLUTIONARY RATE: Given the same amount of nutrients, small cells can have more individuals in a population than larger cells. Thus, more cell division, and more mutation, more evolutionary change. Eukaryotes larger cell size (in general) Different answers for the transport problem 1. lots of internal membrane channels, invaginations and surface area 2. cytoplasmic streaming 3. organelles (compartmentalize cell functions) 4. bulk uptake - endocytosis (phagocytosis/pinocytosis) Introducing a prokaryote that is one million times bigger than E. coli! Sturgeonfish symbiont. Epulopiscium fiseloni 600 µm (0.6 mm) long 20 - 40 µm long Individual flagella twist together to form “thick” flagella Largest known bacterium: Thiomargarita namibiensis Some nearly 1 mm wide Large central vacuole (dark) contains nitrate sequestered to use in the oxidation of reduced sulfur compounds. String of pearls: reflective sulfur granules How do we see microbes? 1. Light Microscopy Up to 1,500 X magnification (yours in lab: 1000 X) Limit of resolving power is ~0.2 µM, or about 1/3 the width of an average bacterial cell Light gathering ability decreases as magnification increases Immersion oil helps gather light rays that would otherwise be lost from specimen How do we see microbes? 2.
    [Show full text]
  • Characterization of Light-Enhanced Respiration in Cyanobacteria
    International Journal of Molecular Sciences Article Characterization of Light-Enhanced Respiration in Cyanobacteria Ginga Shimakawa 1,*,†,‡ , Ayaka Kohara 1,† and Chikahiro Miyake 1,2 1 Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan; [email protected] (A.K.); [email protected] (C.M.) 2 Core Research for Environmental Science and Technology, Japan Science and Technology Agency, 7 Goban, Chiyoda, Tokyo 102-0076, Japan * Correspondence: [email protected]; Fax: +81-78-803-5851 † These authors contributed equally to this paper. ‡ Current address: Research Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8631, Japan. Abstract: In eukaryotic algae, respiratory O2 uptake is enhanced after illumination, which is called light-enhanced respiration (LER). It is likely stimulated by an increase in respiratory substrates produced during photosynthetic CO2 assimilation and function in keeping the metabolic and redox homeostasis in the light in eukaryotic cells, based on the interactions among the cytosol, chloroplasts, and mitochondria. Here, we first characterize LER in photosynthetic prokaryote cyanobacteria, in which respiration and photosynthesis share their metabolisms and electron transport chains in one cell. From the physiological analysis, the cyanobacterium Synechocystis sp. PCC 6803 performs LER, similar to eukaryotic algae, which shows a capacity comparable to the net photosynthetic O2 evolution rate. Although the respiratory and photosynthetic electron transports share the interchain, LER was uncoupled from photosynthetic electron transport. Mutant analyses demonstrated that LER is motivated by the substrates directly provided by photosynthetic CO2 assimilation, but not by glycogen.
    [Show full text]