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| Alga (C) with bacterial prey (P) By: Kamennaya et al, PLOS Biol 2018 |
Download Episode (8.9 MB, 9.7 minutes)
Show notes:
Microbe of the episode: Bradyrhizobium japonicum
Journal Paper:
Kamennaya NA, Kennaway G, Fuchs BM, Zubkov MV. 2018. “Pomacytosis”—Semi-extracellular phagocytosis of cyanobacteria by the smallest marine algae. PLOS Biol 16:e2003502.
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Episode outline:
- Background: Microbes have interesting role in ecosystems
- Both smallest around, bottom of food chain
- But sometimes potentially deadliest to larger organisms – pathogens
- Many slightly larger organisms like to eat smaller microbes
- Called phagocytosis – take inside cell in compartment called vacuole, then digest
- Can then absorb nutrients and eject undigestible components back out
- Works well for prey smaller than predator, but not well for bigger ones
- Some microbes can inject enzymes into larger prey and break down instead of taking inside
- Others can form vacuoles outside their cells, but tricky
- What’s new: Here, scientists publishing in PLOS Biology have figured out how very small algae in the ocean can consume bacteria that are similar in size to themselves!
- Methods: Studying algae called picoeukaryotic algae: Braarudosphaera bigelowii
- Similar in size to some bacteria
- Most of insides taken up by organelles like chloroplasts
- Photosynthesize but get some nutrients from eating bacteria too
- Sorted apart the algae from bacteria by flow cytometry
- Laser used to measure cell characteristics
- Size, fluorescence
- Then separates cells into one receptacle or other
- Verified with sequencing and microscopy
- Hardly any sequences, no visible bacteria
- 84% of the algae seen seemed to have slightly smaller outgrowth of cell
- Kinda like yeast budding off new baby yeast cells
- Looking at cells in various stages, saw algae partially enveloping and consuming bacteria
- Cell structure responsible is cytostome, senses and captures prey
- Called this “pomacytosis”, from Greek poma or plug
- Cos prey plugs hole in cell membrane while being digested
- Summary: Little algae in ocean are preying on bacteria of similar size by enveloping them only partially while digesting; kinda like biting into something and sucking out insides instead of swallowing
- Clarifications if necessary: Not observed in living cells, just inferred from fixed stages
- Possible that actually more membrane closes off inside of alga, not sure
- What do I think: But if true, pretty wild that cells would make big hole in membrane
- Plugged only with foreign cell being digested
- Possible to rip away prey, leaving cell exposed
- Deadly?
- Maybe no worse than regular ways to rip holes in cells
- Also interesting cos algae also have cyanobacterium symbiont totally inside cells
- Fixes nitrogen for host
- But smaller, <5 li="" of="" volume="">
- Vs. >20% from prey cells
- Why do algae need prey? Can photosynthesize
- Probably cos of symbiont: photosynthesis makes O2, O2 inhibits nitrogen fixation
- So to limit O2 generation, take nutrients from prey instead
- Prey can also do some photosynthesis while being pomacytosed even
- Sorta temporary chloroplast
- Being small doesn’t always mean being harmless
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