Lec 5 - Microbial Diversity

• Phylogenetic Diversity


  The component of microbial diversity that deals with evolutionary relationships between microorganisms

  
• Functional Diversity


  The component of microbial diversity that deals with diversity in form and function as it relates to microbial physiology and ecology

  
• Phototrophy


  The use of light energy is prevalent in the microbial world
• Photosynthesis


  Considered the most important biological process

  
• Phototrophs


  Organisms that carry out photosynthesis

  
• Autotrophs


  Photosynthetic organisms that are capable of growing with carbon dioxide as the sole source of carbon
• Photoautotrophs


  Energy comes from light is used in the reduction of CO2 to organic compounds
• Photoheterotrophs


  Phototrophs that use organic carbon as their carbon source
• Phylogenetic diversity is defined on the basis of ribosomal RNA gene phylogeny, which is thought to reflect the phylogenetic history of the entire organism
• Functional Diversity


  • Result from phylogeny and functional traits of microorganism
  • Gene loss - trait present in the common ancestor of several lineages is subsequently lost in some lineages but retained in others that over evolutionary time became quite divergent
  • Convergent evolution - trait has evolved independently in two or more lineages and is not encoded by homologous genes shared by these lineages
  • Horizontal gene transfer (HGT) - genes that confer a particular trait are homologous and have been exchanged between distantly related lineages
• Photoautotrophy


  1. Light reactions producing ATP

  2. Light-independent dark reactions reducing CO2 to cell material for autotrophic growth
• Chlorophylls


  Present in plants, algae, and cyanobacteria
• Bacteriochlorophylls


  Present in anoxygenic phototrophs

  
• Oxygenic photosynthesis


  The photosynthetic process in cyanobacteria (and chloroplasts)
• Anoxygenic photosynthesis


  O2 is not produced
• Absorption of light energy by chlorophylls and bacteriochlorophylls begins the process of photosynthetic energy conversion, and the net result is chemical energy, ATP
• Phototrophic bacteria


  • Proteobacteria
  • Chlorobi
  • Chloroflexi
  • Firmicutes
  • Acidobacteria
  • Gemmatimonadetes

  
• Phototrophic bacteria


  • Use chlorophyll-like pigments to harvest energy from light and transfer this energy in cytoplasmic membrane to increase the amount of pigment for better use of light of low intensities for the production of ATP
  • Couple light energy to carbon fixation through a variety of different mechanisms but not all phototrophs fix CO2
• Types of photosynthetic reaction centers

  • Type I reaction centers (FeS-type)
  • Type II reaction centers (quinone-type, or Q-type)
• Both types of reaction centers are present in Cyanobacteria whereas only one type or the other is present in anoxygenic phototrophs

  
• Cyanobacteria


  • Both unicellular and filamentous
  • 0.5 µm in diameter, as large as 100 µm in diameter
  • First oxygen evolving phototrophic organisms on Earth
  • Oxygenic phototrophs, have both FeS-type and Q-type photosystems
  • Some can assimilate simple organic compounds such as glucose and acetate if light is present, a process called photoheterotrophy
  • Have specialized membrane systems called thylakoids that increase the ability of cells to harvest light energy
  • Cell wall contains peptidoglycan and is structurally similar to that of other Gram-negative bacteria
  • Have photopigments, fluorescent and emit light when visualized using a fluorescence microscope

  
• Phycobilins


  Photopigments that function as accessory pigments in photosynthesis
• Phycocyanin


  Responsible for the blue-green color of most cyanobacteria

  
• Phycoerythrin


  Species producing phycoerythrin are red or brown

  
• Cyanobacteria


  • Exhibit gliding motility
  • Some filamentous cyanobacteria form hormogonia - short, motile filaments that break off from longer filaments to facilitate dispersal in times of stress
  • Some form akinetes - cells with thickened outer walls

  
• Nitrogen-fixing cyanobacteria


  • Cyanothece and Crocosphaera - fix nitrogen only at night when photosynthesis does not occur
  • Trichodesmium - fix nitrogen during the day
  • Nostocales and Stigonematales - facilitate nitrogen fixation by forming specialized cells called heterocysts
• Synechococcus and Prochlorococcus are the most abundant phototrophs in the oceans

  
• Morphological groups of cyanobacteria

  • Chroococcales - unicellular, dividing by binary fission
  • Pleurocapsales - unicellular, dividing by multiple fission (colonial)
  • Oscillatoriales - filamentous non-heterocystous forms
  • Nostocales - filamentous, divide along a single axis, and are capable of cellular differentiation
  • Stigonematales - morphologically similar to Nostocales except that cells divide in multiple planes, forming branching filaments

  
• Marine nitrogen-fixing cyanobacteria


  • Crocosphaera - dominate nitrogen fixation in most of the Pacific Ocean and are widespread in tropical and subtropical habitats
  • Trichodesmium - dominant nitrogen-fixer in the North Atlantic Ocean and parts of the Pacific where dissolved iron concentrations are elevated
  • Calothrix and Richelia - form symbiotic associations with diatom found in tropical and subtropical oceans
  • Nodularia and Anabaena - dominate nitrogen fixation in cold waters of the Northern Hemisphere and are often observed in the Baltic Sea
• Purple sulfur bacteria


  • Anoxygenic phototrophs that use hydrogen sulfide (H2S) as an electron donor for photosynthesis
  • Found in lakes, marine sediments, and "sulfur springs," where H2 produced can support the growth of purple sulfur bacteria; Also found in microbial mats and salt marsh sediments
  • Use a Q-type system that contain either bacteriochlorophyll a or b, and carry out CO2 fixation by the Calvin cycle

  
• Families of purple sulfur bacteria

  • Chromatiaceae - store sulfur granules in the periplasmic space and have vesicular intracellular photosynthetic membrane systems
  • Ectothiorhodospiraceae - oxidize H2S to S0 that is deposited outside the cell have lamellar intracellular photosynthetic membrane systems

  
• Purple non-sulfur bacteria


  • Most metabolically versatile of all microbes
  • Photoheterotrophs - a condition where light is the energy source and an organic compound is the carbon source
  • Use a Q-type photosystem and contain either bacteriochlorophyll a or b
  • Can conserve energy through a variety of metabolic processes
  • All members can fix N2 and will thrive under such conditions, rapidly outcompeting other bacteria

  
• Aerobic anoxygenic phototrophs are a group of bacteria that can use light energy to supplement their metabolism but do not carry out oxygenic photosynthesis
• Sulfate


  Abundant levels
• Genera


  • Ectothiorhodospira
  • Halorhodospira
• Species


  • Ectothiorhodospira vacuolata
  • Halorhodospira spp.

  
• Purple Non-Sulfur Bacteria


  Key Genera: Rhodospirilum, Rhodoferax, Rhodobacter

  
• Species


  • Rhodospirilum rubrum
  • Rhodoferax ferrieducens
  • Rhodobacter sphaeroides
• Purple Non-Sulfur Bacteria are the most metabolically versatile of all microbes

  
• Purple Non-Sulfur Bacteria are not always purple. They synthesize an array of carotenoids that can give them colors like purple, red, or orange