BIOL 2004 Lecture Notes - Lecture 4: Actinobacteria, Firmicutes, Anaerobic Respiration
3 May 2018
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Diversity of Bacteria
March 8-10, 2016
Prokaryote “Species”
• Animals & plants: ideal of biological species concept based on interfertility
• In prokaryotes, no true sexual process
o By necessity, species are based on operational criteria (e.g. >97% 16S rRNA
identity threshold)
• ~10,000 named to date
o demanding rules (must be cultured)
o each species encompasses much more genomic diversity than in animals or plants
• do not worry about ranks for groups
• bacteriologists often italicise higher taxa as well
o names can be used to describe shape. (rod = bacillus) **see slide
Patterns of Prokaryote Evolution
• some groups are distinguished by major cellular or physiological traits
o Bacteria vs Archaea
o Spirochetes (periplasmic flagella)
• But many major biological traits appear in very distant related organisms
o Must is due to horizontal (lateral) gene transfer
▪ Transfer from both closely and distantly related species
▪ E.g. some archaea with >10% of their genome originally from bacteria
▪ Operon structure would help the acquisition of novel traits by horizontal
gene transfer
Examined Groups of Bacteria:
• Gram positives (Firmicutes & Actinobacteria)
• Spirochetes
• Proteobacteria
• Cyanobacteria
Gram-Positives
• 2 groups: Firicutes and actinobacteria *may not be closely related
• gram-positive cell envelope (no outer membrane)
• Firmicutes:
o Thick cell wall
o Majority are organotrophs
o Range from obligate aerobes – obligate anaerobes
o Many are specialist fermenters
o Most common in soil and sediments
o Thick wall to resist water conditions
o Examples:
▪ Lactic acid bacteria
• Aerotolerant anaerobes
find more resources at oneclass.com
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• Usually no respiration
• Ferment simple sugars to lactic acid (lactate) = homolactic
fermentation
• Ex. Streptococcus
• Habitats:
o Carbohydrate-rich material aka:
o Decaying plant material
o Mouth, gastrointestinal tract, vagina
o Pickling and dairy industries – acid production inhibits
other microbes
▪ Endospore formers (bacillus, clostridium)
• Ex. Bacillus
o Mostly found in soil/sediment
o Endospores in a dormancy state
o Endospores: very resistant to heat, desiccation, UV…etc
• A think cortex od modified peptidoglycan and protein coat cell and
surround the core
• The core contains nucleoid and inactive cytoplasm, with very low
water contact
• Formation:
o Reproduce normally through binary fission
o Sporulation = differentiation/production of a spore
▪ DNA replication
▪ Unequal division inside cell wall: Axial filament
splits into forespore and motherspore **uneven
▪ Mother cell engulfs forespore
▪ Cytoplasm is reduced, cortex forms
▪ Mother cell degenerates
▪ thick peptiglycan cortex forms; coat proteins are
deposited
▪ DNa stabilizing protein incorporated into core
▪ Spores are then released
▪ Overall, 1 cell = 1 spore **differentiation
• Actinobacteria
o Organotrophs: generally aerobic
o Abundant in soil
o Most are filamentous (e.g. Streptomyces)
o Some are unicellular (e.g. mycobacterium – tuberculosis; leprosy)
o Filamentous Actinobacteria
▪ Filaments often not divided into distinct cells
▪ Can usually branch and extend as mycelium (many copies of genome)
▪ Usually produce thick-walled spores (‘arthrospores’)
• Resist desiccation
• Different from endospores of Firmicutes *Differentiation vs.
Binary Fission
o Form by multiple fission
find more resources at oneclass.com
find more resources at oneclass.com
