7 P52220RA Turn over 22. What we ultimately find is confirmation of a bizarre biological partnership operating at the edge of what is energetically possible. As has been found at other methane seep sites around the world, certain types of archaea and bacteria aggregate together in multicellular clumps, with tens, hundreds, or occasionally thousands of microbes linked by mutual energetic necessity. The details of the association are still up for debate, but it appears that archaeal partners oxidize methane and transfer electrons to the bacteria to enable the reduction of sulfate to sulfide, generating energy to power cellular functions. Remarkably, when the energetics numbers are crunched, the archaea come out in the red—their half of the arrangement does not appear to produce enough energy for their own survival. This means that the sulfate-reducing reaction performed by their bacterial partners must supply power to both species. How this mutualism works, especially in an evolutionary framework, is far from certain. 23. The energetic demands for biosynthesis are relatively low given these organisms’ very slow rates of growth, doubling only every few months. Nevertheless, given the difficulty of extracting and sharing energy in methane seep environments, anaerobic methane-oxidizing partnerships deserve the title of extremophiles, as characterized by the energetic framework. Hopefully, future studies will illuminate the nature of this symbiosis and provide insight into how the energetically improbable becomes possible, untangling the intricacies of these and other slow-growing extremophiles. An impossible situation Low energy availability, high energy requirements 24. The final permutation of energetic cost-benefit ratios seems like a non-starter: having higher energy demands than the rates of supply does not make for a sustainable situation. And while growth under such conditions seems impossible (with the notable exception of tightly-coupled metabolisms like those described above), an energy debt need not mean cell death. 25. When the going gets tough, some microbial species, such as the bacterium Bacillus subtilis, initiate a hibernation protocol, shutting down the furnace and turning off the lights before forming a life raft that will hopefully ferry them to greener pastures. The process is called sporulation, and it’s a life-or-death decision not to be made lightly. B. subtilis is commonly found in soil environments susceptible to feast or famine swings in energy availability. When one of these cells senses nutrient stress, it draws on energy stores, activating flagella to search for food, flooding its surroundings with antibiotics to kill off competitors, or desperately importing foreign pieces of DNA in hopes that a novel capability will be the ticket out of a bad situation. If all else fails, it replicates its genetic material and partitions it into a protective capsule that can withstand extreme heat, radiation, chemical stress, desiccation, and energetically untenable conditions. Sensors located on the spore’s outer surface probe the environment for friendlier surroundings and assess the possibility of returning to a more active way of life. Powering up is an extremely energetically demanding undertaking, permitting full resurrection only under ideal circumstances. Thus, while this behavior may be considered extreme in itself, spore formers dodge the true test of their extremophilic nature by waiting out the impossible in a state of metabolic hibernation.