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Microbial Iron Oxide Respiration

53:30 recording · AUTO · 4 speakers

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Brief overview

Microbes actively link the iron and sulfur cycles, and bacteria can spread without flagellar propulsion.

  1. Microbes beat the rocks at sulfide oxidationBiological iron oxide respiration outpaces the abiotic chemical reaction at environmentally relevant sulfide concentrations, making it ecologically real rather than a lab curiosity.
  2. Bacteria can migrate without working flagellaSalmonella with broken hooks or filaments still spread across 0.5% agar; only losing the MotA motor stopped them, which is itself still unexplained.
  3. Sometimes the answer in biology is physicsAcidic waste products change osmolarity, water flows out of the agar, and the colony edge surfs forward without any propulsion.
Executive Summary AI
  • Michael Schmidt opens with an open access paper from the October 23rd issue of Nature, "Microbial Iron Oxide Respiration Coupled to Sulfide Oxidation" by Chen, Li, Battisti and colleagues, which he says will rewrite the textbooks on global element cycling by connecting iron, sulfur and oxygen.4:50
  • The authors surveyed the metabolism across 37 different prokaryotic phyla and predicted it in over 5,561 species across 71 file, then validated it with the cultivated Desulfovibrio alcaliphilus, which grows by breathing solid iron oxide, fixes CO2 and turns toxic sulfide into harmless sulfate using multi-heme cytochromes that act as microbial nanowires.9:07
  • Petra Levin then presents a paper published that same week, "Swashing: A Propulsion-Independent Form of Bacterial Surface Migration" by Dustin Panich, Eric Dudabout, David Blair and Navish Wadhwa, all affiliated at some point with Arizona State University, where the lab sits in the physics department.22:49
  • What they describe began as an unintended negative control: salmonella carrying mutations in the flagellar hook or filament still migrated out on 0.5% agar at about half the speed, and only deleting the motor protein MotA stopped movement, while deleting motor and filament together restored it.28:16
  • The explanation is metabolic and physical rather than motor-driven: cells dumping acetate and formate from overflow metabolism acidify the plate from pH 6.86 in the medium to 6.1 at the edge and 5.35 in the centre, raising osmolarity so water is pulled out of the agar and the colony front rides its own wave, which the authors call swashing.39:10
Key Quote
“I'm actually buzzing about this paper.”
— Michael Schmidt5:40
Key Quote
“Chemolithotroph means they're literally eating rocks, folks.”
— Michael Schmidt10:52
Key Quote
“They live on air and rock.”
— Petra Levin12:57