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| By: Rang et al, 2018 mSphere 3:e00428-18 |
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.
Other interesting stories:
- Gut microbe can help protect mice from colon cancer (paper)
- Microbes living in super-dry desert couldn't survive excess rains
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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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