6 P52220RA 18. Streptomyces capture organic molecules largely by secreting enzymes into the soil to access and degrade energy-rich polymers before other competitors can get to them. It’s a bold strategy susceptible to freeloader hijacking, with no guarantee that the processed material will find its way back to the same organism that went to the trouble of producing the enzyme. But at scale, the odds become more palatable, and the benefit from degraded organics that find their way to one Streptomyces or another outweighs the inefficiency of the strategy. Building a large network of interconnected cells is the only option that makes this spendthrift approach worthwhile. 19. Oxygen is the highest-potential electron acceptor on the market, and transferring electrons to O2 provides the biggest payoff per electron-donating molecule. This makes the upper, oxygen- perfused layers of soil highly sought-after real estate, but it comes at a price. In a 2005 study, geomicrobiologists Tom McCollom of the University of Colorado, Boulder, and one of us (Amend, then at Washington University in St. Louis) calculated the energetic costs of synthesizing an extensive list of biomolecules, including amino acids, nucleotides, fatty acids, saccharides, and amines, from inorganic precursor molecules. We found that biosynthetic costs were actually higher—by more than an order of magnitude—in oxygen-infused conditions than in anaerobic settings. Part of this discrepancy is due to the fact that many precursors must be reduced from their oxidized state prior to biomolecular construction, but it suggests that the energetic windfall from using oxygen as an electron acceptor may be a necessary copay, not a bankable nest egg. 20. Perhaps Streptomyces’s most impressive adaptation is the genus’s remarkable array of antibiotics, which can attack competitors’ cell walls or protein-synthesis machinery. But these large, sophisticated weapons require a high flux of electron-rich intermediates and the repurposing of cellular supply chains. An analysis led by J. Stefan Rokem of the Hebrew University of Jerusalem showed that antibiotic production represents an enormous drain on biosynthetic pathways, frequently costing more than half of the stocked supply of precursor building blocks (such as pyruvate or acetyl-CoA) that would otherwise be used to construct biomass and generate new cells. But, while expensive, antibiotic synthesis is critical for survival in this crowded environment, minimizing competition for much-needed resources. From an energetic perspective, Streptomyces is an extreme organism, and it’s hiding in plain sight. Just getting by Low energy availability, low energy requirements 21. As Jason is hauled back on deck, packed to the brim with samples from deep-sea methane seeps, Atlantis becomes a hive of activity. We rush the cores of seafloor sediment along with chunks of carbonate rocks to the onboard laboratory, where they’re partitioned and allocated for experiments. Liquid is extracted for geochemical measurements, and a few grams of sediment are frozen for DNA and microscopic analyses. A separate aliquot is scooped into a shiny silver mylar bag, mixed with filtered seawater and isotopically labeled chemicals, and flushed with nitrogen and methane gas. The bag is heat-sealed and set aside, a time capsule to be opened several months later to determine how much of the isotope-labeled substrate has been taken up by the mysterious process of anaerobic methane oxidation.