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Sunday, 08 July 2018 20:50

Prokaryote Prey Plug Picoalgae - BacterioFiles 346

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Published in Bacteriofiles

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: 

bf346picoalgaeMicrobe 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,
    • 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
Last modified on Sunday, 08 July 2018 20:55
Jesse Noar

Jesse Noar is microbiologist with a PhD from North Carolina State University and Bachelor's from Cornell. Most of his research has focused on the amazing abilities and potential uses of bacteria, especially those found in soil. Jesse hosts the BacterioFiles podcast highlighting the most interesting recent microbiology research on all kinds of different microbes, part of the ASM family of podcasts. Learn more at asm.org/bacteriofiles or at www.bacteriofiles.com.

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