Microbial Diversity

• 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 - The component of microbial diversity that deals with evolutionary relationships between microorganisms.
• Phylogenetic Diversity - Encompasses the genetic and genomic diversity of evolutionary lineages and so can be defined on the basis of either genes or organism
• Phylogenetic diversity is defined on the basis of ribosomal RNA gene phylogeny, which is thought to reflect the phylogenetic history of the entire organism
• The component of microbial diversity that deals with diversity in form and function as it relates to microbial physiology and ecology
• 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 - The process by which organisms convert radiant energy into biologically useful energy and synthesize metabolic compounds using only carbon dioxide or carbonates as a source of carbon
• Two distinct sets of reactions:

  1. Light reactions producing ATP
  2. Light-independent dark reactions reducing CO2 to cell material for autotrophic growth
• Photosynthesis requires light sensitive pigments.
• 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 microorganisms, those microbes that conserve energy from light
• First phototrophic organisms were anoxygenic phototrophs, organisms that do not generate O2 as a product of photosynthesis.
• Instead of H2O, these organisms likely to used H2 , ferrous iron (Fe2+), or H2S as the electron donor for photosynthesis
• Anoxygenic photosynthesis is present in six bacterial phyla: the Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, Acidobacteria, and Gemmatimonadetes.
• All phototrophic bacteria use chlorophyll-like pigments to harvest energy from light and transfer this energy in cytoplasmic membrane
• The two different types of photosynthetic reaction centers are (a) type I reaction centers (FeS-type) and (b) type II reaction centers (quinone-type, or Q-type)
• Cyanobacteria - Oxygenic phototrophs, have both FeS-type and Q-type photosystems
• Cyanobacteria can assimilate simple organic compounds such as glucose and acetate if light is present, a process called photoheterotrophy.
• Cyanobacteria 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
• Photopigment 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 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.
• Cyanothece and Crocosphaera –fix nitrogen only at night when photosynthesis does not occur
• Trichodesmium – fix nitrogen during the day