Session 5 - Diversity

• Phototrophs - organisms that carry out photosynthesis.
• Autotrophs - 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.
• Phylogenic diversity - is the component of microbial diversity that deals with evolutionary relationships between microorganisms.
• 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 is the component of microbial diversity that deals with diversity in form and function as it relates to microbial physiology and ecology.
• Gene loss, Convergent Evolution & Horizontal Gene Transfer 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 to or more lineages and is not encoded by homologous genes shared by these lineages.
• Horizontal gene transfer - genes that confer a particular trait are homologous and have been exchanged between distantly related lineages.
• Photoautotrophy - is the process by which organisms convert radiant energy into biologically useful energy and synthesize metabolic compounds using carbon dioxide or carbonates as a source of carbon.
• Two (2) distinct sets of reactions:

  1. light reactions that produce ATP;
  2. light-independent dark reactions that reduce CO2 to cell material for autotrophic growth.
• Photosynthesis requires light-sensitive pigment:

  1. chlorophylls - present in plants, algae, and cyanobacteria
  2. bacteriochlorophylls - present in anoxygenic phototrophs
• Oxygenic photosynthesis - the photosynthetic process in cyanobacteria.
• Anoxygenic photosynthesis - O2 is not produced.
• First phototrophic organisms were anoxygenic phototrophs, organisms that do not generate O2 as a product of photosynthesis.
• Anoxygenic photosynthesis is present in six bacterial phyla: the Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, Acidobacteria, and Gemmatimonadetes.
• Two (2) different types of photosynthetic reaction centers:

  1. type I reaction centers (FeS-type)
  2. type II reaction centers (quinone-type, or Q-type)
• Both types of photosynthetic reaction centers are present in Cyanobacteria whereas only one type or the other is present in anoxygenix phototrophs.
• Key Genera of Cyanobacteria:

  Prochlorococcus, Crocosphaera, Synechococcus, Trichodesmium, Oscillatoria, Anabaena
• Cyanobacteria

  • both unicellular and filamentous
  • 0.5 um in diameter, as large as 100 um in diameter.
  • First oxygenic evolving phototrophic organisms on Earth.
  • have both FeS-type and Q-type photosystems.
  • some can assimilate simple organic compounds such as glucose and acetate light is present, a process called photoheterotrophy.
  • have specialized membrane systems called thylakoids.
  • cell wall contains peptidoglycan, and is similar to gram-negative bacteria
• Cyanobacteria have photopigment which produces chlorophyll a, known as phycobilins, function as accessory pigments in photosynthesis.
• Phycocyanin - responsible for the blue-green color of most cyanobacteria.
• Phycoerythrin - species producing this pigment are red or brown.
• Cyanobacteria exhibits gliding motility.
• Some filamentous cyanobacteria form hormogonia, short, motile filaments that break off from longer filaments to facilitate dispersal in times or stress.
• Some cyanobacteria form Akinetes - cells with thickened outer ealls.
• 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.
• Five (5) Morphological Groups of Cyanobacteria:

  1. Chroococapsales
  2. Pleurocapsales
  3. Oscillatoriales
  4. Nostocales
  5. Stigonematales
• 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.
• Synechococcus and Prochlorococcus - the most abundant phototrophs in the oceans.
• Two (2) groups of Marine nitrogen fixation:

  1. Crocosphaera
  2. Tricodesmium
• Crocosphaera - dominate nitrogen fixation in most of the Pacific Ocean and are widespread in tropical and subtropical habitats.