Monday, July 9, 2018

BacterioFiles 346 - Prokaryote Prey Plug Picoalgae

Alga (C) with bacterial prey (P)
By: Kamennaya et al,
PLOS Biol 2018
This episode: Very small ocean algae consume bacterial prey of a similar size to themselves by engulfing them only partially!

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.

Other interesting stories:

  • Using nanomagnets to control quorum sensing by pulling bacteria together (paper)

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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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