Monday, December 17, 2018

BacterioFiles 366 - Globules Get Garbage Gone

By: Rang et al, 2018
mSphere 3:e00428-18
This episode: Bacteria rid themselves of burdensome waste by ejecting it inside little pieces of their own cell, called minicells!

Download Episode (10.8 MB, 11.9 minutes)

Show notes:
Microbe of the episode: Cacao yellow mosaic virus

News item

Journal Papers:
Rang CU, Proenca A, Buetz C, Shi C, Chao L. 2018. Minicells as a Damage Disposal Mechanism in Escherichia coli. mSphere 3:e00428-18.

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Episode outline:

  • Background: Bacteria don't have circulatory system or digestive tract
    • No waste disposal like we think of it, with toilets
  • But still have junk inside that needs to go out
    • Unwanted metabolic products, damaged molecules, etc
    • Sometimes just floats out through membrane and wall
    • Sometimes can break down and recycle
    • But not all molecules can get through or can be recycled
  • What’s new: Now, scientists publishing in mSphere have discovered that bacteria can rid themselves of waste molecules by breaking off pieces of their cells!
  • Minicells – little pieces of bacterial cytoplasm with membranes and cell walls
    • No chromosomal DNA, but can have proteins, RNA, plasmids
    • So can function like cells to some extent, but not self-replicate
    • Wondered: why do cells produce them?
  • Known that E. coli produces in response to stress like radiation
    • Otherwise unusual to see in lab conditions
  • Methods: Compared normal E. coli with mutant that makes more minicells
    • Exposed to streptomycin or not; not lethal amount, just stressful
    • Causes clumps of damaged protein, visualized under microscope
    • Mutants grew a little slower but still grew; antibiotic didn't inhibit rate
    • Antibiotic did increase mutant's minicell production
  • Wanted to see if minicells more associated with old poles and old daughters
    • Old pole – rod-shaped cell, divides in half, each new cell has end present before and new end
    • Old daughter – when cell divides, one daughter gets old pole, other gets new
      • So both same age, but one has new and old pole, other has new and older pole
    • Old poles have more damaged/waste molecules
    • Watching cells proliferate, can track old and new
    • Found that old daughters make a little more minicells, only with no antibiotic
    • Made from old poles a lot more often in both conditions, both old and new daughters
  • Is waste ejected inside? Added fluorescent tags to damaged proteins and cell wall
    • Grew with wall tag for a while, then removed, so any new growth wouldn't fluoresce
    • Found cells grow from middle, old stuff on ends
  • Tagged damage with chaperone-fluorescence fusion
    • Saw it accumulate at 1 end of cell, then exit in minicell
  • But does it benefit cells? Measured doubling times (not counting minicells), growth rate
    • Cells that made minicells took longer to divide (makes sense, extra growing)
    • But their daughter cells had faster growth, esp with antibiotic
    • So disadvantage to parent but advantage to offspring
      • From getting rid of burdensome waste instead of passing it on
  • Over range of antibiotic concentrations, minicell mutant had advantage over normal strain
    • But disadvantage at very low/0
    • Even in competition in mixed cultures, mutant had advantage with antibiotics
  • Summary: Breaking off little pieces of their cells as trash bags helps bacteria be healthier by disposing of burdensome cellular waste
  • Applications and implications: Relevant to antibiotic resistance
  • Also interest in using minicells as delivery for pharmaceutical
    • Understanding regulation in bacteria could help engineer cells that produce specific kinds
    • Synthesize and encapsulate material for delivery
    • Put antibodies targeting cancer on surface, for example
  • What do I think: Like reversing aging process
    • Get rid of old, damaged material
    • Imagine if we could do the same
    • Harder to do regeneration when multicellular, risks cancer
  • Comes at cost though: have to regrow materials damaged and also used for disposal
    • Pay for electricity for putting stuff down garbage disposal vs. just composting
    • But more quickly/thoroughly disposed, no longer smelly
  • Pretty good ability to have, what if we could just drop off excess body material

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