Lecture 17

Question 1

life cycle of prosthecate bacteria

Answer 1

• caulobacter, hyphomicrobia
  -> stalked/prosthecate cell morphology
  -> budding cell division
• motile swarmer cells and sessile stalked cells
• tad pili attach to surface and become holdfast
• swarmer cells must differentiate to divide
  -> loss of flagellum and pili
  -> attachment to surface and growth of stalk
• poor nutrient = longer stalk (better access in low nutrient environment)
  flagellar rotation -> tad pili synthesis -> swarmer cell -> flagellum shedding -> stalk formation

Question 2

pseudomonadota aka proteobacteria

Answer 2

• metabolically diverse
  -> phototrophs, chemoorganotrophs, chemolithotrophs, heterotrophs, autotrophs, diazotrophs
  -diverse morphology
  -> cell division, differentiation
• many important environmental members
  -> nitrifying bacteria
  -> anoxygenic bacteria
  ->iron and sulfur bacteria
  -> methanotrophs and methylotrophs
  -> symbiotic nitrogen fixation
• important pathogens
  -> agrobacterium = plant pathogen causing crown gall, and other diseases in plants
  -> rickettsia = rocky mountain spotted fever, typhus
• yersinia = plague

Question 3

bdellovibrio life cycle

Answer 3

• predators of gram negative bacteria
• alternates between predatory phase and intracellular reproductive phase
• uses host contents as carbon, nitrogen, energy sources, uses fatty acids and nucleotides directly in biosynthesis
• grows into filament that undergoes multiple fission
• takes 3-4 hours
• drills a whole in outer membrane then loses flagella, inhibits host DNA replication

Question 4

nitrifying bacteria

Answer 4

• AOB = nitrosomonas, nitrosospira, nitrosococcus
• NOB = nitrobacter, nitrococcus, nitrospira
• extensive intracytoplasmic membranes allow greater surface area for metabolism as they need to oxidize larger amounts of substrate to fuel carbon fixation
• key organisms in the nitrogen cycle - important in agriculture, wastewater treatment, marine environments
• different species specialize in different environments

Question 5

features of nitrifying bacteria and the environment they are found in

Answer 5

nitrosomonas - peripheral, lamellar, soil sewage, freshwater, expansion of plasma membrane to increase surface area to carry out more processes

nitrosococcus - centrally located parallel bundle, lamellar, obligately marine

nitrobacter - polar cap of flattened vesicles in peripheral region of the cell, soil, freshwater

nitrococcus - tubular cytomembranes randomly arranged in cytoplasm, marine

Question 6

nitrification

Answer 6

• microbial oxidation of NH4+ to NO3- with oxygen as TEA
• ammonia oxidizing bacteria and archaea
  -> ammonia monooxygenase
• nitrite oxidizing bacteria
  -> nitrite oxidoreductase

Question 7

rickettsia

Answer 7

• exclusively intracellular parasites or mutualistic symbionts
• intracellularity is associated with genome reduction (0.8-2.3Mbp)
• zoonotic pathogens with arthropod vectors
• enter host through insect saliva and are taken up by phagocytosis

Question 8

origin of mitochondria

Answer 8

• phylogenetic analysis of mitochondrial genomes indicates that mitochondria come from the alpha-PB
• lineage is unclear because of limited genome size
  -> related to rickettsia or rhodobacterales (purple non sulfur bacteria)
• intracytoplasmic membranes of rhodobacterales have similar morphology to mitochondrial cristae
• rickettsia are common symbionts or protozoa and this relationship resembles that of mitochondria
• ICMs are widespread in alpha-PB not limited to rhodobacterales