Microbial Diversity

• Prokaryotes


  • Bacteria
  • Archaea
• Eukaryotes


  • Protozoans
  • Algae
  • Fungi

  
• Other microbes


  • Virions
  • Viroids
  • Prions
• Bacteria


  Unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal

  
• Gram-negative bacteria


  Bacteria that do not stain with crystal violet dye
• Gram-positive bacteria


  Bacteria that stain with crystal violet dye
• Proteobacteria


  • Largest phylum of domain Bacteria; vast variety of morphologies and physiologies
  • Pathogenic and nonpathogenic
  • Evolutionary root of mitochondrion within the phylum

  
• Cyanobacteria


  • Commonly known as "blue-green algae" but are prokaryotic
  • Lack membrane enclosed chloroplasts which distinguish them from other algae which are eukaryotic
  • Group of gram negative, autotrophic microorganisms that contain photosynthetic pigments (chlorophyll, phycocyanin)
  • Capable of reproducing only asexually

  
• Cyanobacteria: Distinguishing characteristics


  • Most species secrete a mucilaginous substance which envelop the cells or filaments in the form of sheath or matrix
  • Vegetative cells are relatively undifferentiated; however, some developed differentiated cells in the form of heterocysts and akinetes
  • Heterocyst - site for nitrogen fixation under aerobic conditions; formed in response to a lack of fixed nitrogen (NH4 or NO3) in filamentous cyanobacteria
  • Trichome - chain of cells formed by binary fission in a single plane where cells remain attached to one another after cell division
  • Akinete - nonmotile cells characterized by their enlarged size with respect to vegetative cells, has thick cell wall and additional tegumentary layers, with high content of nitrogen reserves in the form of cyanophycin granules

  
• Cyanobacteria: Morphology

  • May be solitary, colonial, or joined together in filaments
  • Trichome filaments: homocystous (undifferentiated); heterocystous (differentiated). Some have spirally coiled filament
  • Flagellar motility is absent but gliding movements are known to some

  
• Archaea


  Most are extremophiles
• Archaea


  • Euryarchaeota
  • Crenarchaeota
• Protozoans


  • Animal-like, single-celled eukaryons that lack tissue specialization
  • Many are aerobic and majority are heterotrophs
  • They feed on other microorganisms and on small particulate matter
  • In general, they reproduce asexually and are motile (they lack cell walls)
  • May form cysts under adverse conditions and become active (trophic form) again when conditions are favorable
• Protozoans (based on motility)

  • Sarcodina or amoebae
  • Mastigophora or flagellates
  • Ciliates

  
• Pseudopodia


  • Flowing protoplasmic projections
  • Amoeboid movement: formation of pseudopodia

  
• Flagella


  • Whip-like structures
  • Can be located singly at one cell pole (monotrichous), at both poles (amphitrichous), in large numbers along the length of the cell (peritrichous), or as a tuft of flagella at a polar end (lophotrichous)
• Cilia


  • Short, hair-like structures for movement and food-getting
• Cysts


  • Protective structures formed by protozoans under adverse conditions
• Algae


  • Photosynthetic, eukaryotic organisms
  • Lack tissue differentiation (in contrast to plants)
  • Have distinct, visible nuclei and chloroplasts
  • Exhibit a wide range of thallus types and degree of complexities of structure
  • Can reproduce sexually or asexually

  
• Algae: Distinguishing characteristics

  • Chloroplast - site for photosynthesis
  • Organelles that contain chlorophyll a and other pigments (e.g., chlorophyll b and c, fucoxanthin, xanthophyll)
  • Pellicle - semirigid, outer structure present in Euglenoids in place of cell wall, making them flexible in movement; gives the organism a definite form
  • Eyespot / Stigma - photoreceptive organelle

  
• Algae: Morphology

  • May be unicellular, colonial, or filamentous
  • Flagellar motility may be present
  • Coenobium - loose association of unicellular organisms that live in a colony and may be surrounded by a common membrane

  
• Fungi


  • Heterotrophic, eukaryotic, achlorophyllous organisms
  • Typically saprozoic (feeding on dead organic matter)
  • Can reproduce sexually or asexually
  • Filamentous forms are often referred as molds, while unicellular forms are frequently called yeasts
• Fungi: Distinguishing characteristics

  • Hypha - branching, filamentous structure; may be septate or non-septate
  • Mycelium - mass of hyphae
  • Spore-bearing structures
  • Spores - microscopic biological particles that allow fungi to be reproduced (analogous to seeds in plants)
  • Asexual spores - e.g., sporangiospores, conidiospores
  • Sexual spores - e.g., ascospores, basidiospores
  • Phialide
  • Vesicle
  • Foot cell

  
• Fungi: Morphology

  • May be unicellular or filamentous
  • Flagellar motility is absent (except in some gametes)
  • Mold or yeast forms; dimorphism
• Archaea are also prokaryotes but differ from bacteria in their cell wall composition (lack peptidoglycan) and metabolic pathways.
• Bacteria are prokaryotic cells that lack membrane-bound organelles, have circular DNA, and reproduce by binary fission.
• Bacteria can have different shapes including cocci (spherical), bacillus (rod-shaped), spirilla (spiral-shaped), vibrio (curved rod-shaped), and mycobacteria (wavy).
• Protists are eukaryotic cells with diverse morphologies and functions, including photosynthesis, heterotrophy, parasitism, and symbiosis.
• purpose of mucilaginous substance secreted by cyanobacteria?

  to envelop cells in the form of sheath or matrix
• Euryarchaeota 


  methanogens, extreme halophiles, thermoacidophiles, and some are hyperthermophiles
• Crenarchaeota 


  hyperthermophiles and extreme opposites, chemolithotrophs that use ammonia as energy source. Some lives in soil and freshwater
• Sarcodina or Amoebae


  move by means of pseudopodia
• Mastigophora


  have one or more flagella
• Fucoxanthin


  yellow-orange carotenoid pigment found in brown and golden-brown algae
• Virions

  • entire virus particle
  • representation of a virus in its extracellular, infectious form
• RNA/DNA 


  viral genome
• capsid


  protective protein coat in viruses

  may be surrounded by outer lipid envelope
• Viroids

  • naked molecules of infectious RNA
  • do not encode protein
  • virus-like infectious agents (mainly of plants)
  • can be enzymatically active (acts as ribozymes)
• Prions

  • devoid of genetic material
  • misfolded; disordered proteins
  • pathogenic agents that are able to induce abnormal folding of normal cellular proteins
  • causes of some fatal neurodegenerative diseases
• Spongiform encephalitis


  tiny holes, give out "sponge" appearance in the brain