Just as microbes in our guts digest the complex fibers we eat, marine bacteria break down and digest the complex forms of organic matter that phyto- and zoo-plankton produce in the surface ocean. This biological process is key for life on the planet, as it returns carbon back to the atmosphere and balances the elemental cycles that sustain life. Complex organic matter is made up of long polymer chains packed in matrices, which cannot be directly absorbed by cells. Instead, bacteria need to first excrete enzymes that digest polymers into smaller, soluble molecules, a process that triggers a surprising cascade of microbial interactions that determine the mode and tempo of carbon consumption. In this talk I will focus on three key type of interactions that define this process: the transfer of carbon between different species of bacteria occupying well-defined metabolic guilds, the awakening of dormant viruses in the genomes of polymer degraders, and the emergence of cooperative, multicellular cell structures within which polymer-degrading organisms divide metabolic labor. Throughout my talk, I will highlight how studying these natural, polymer-degrading ecosystems can inform emerging efforts in microbiome engineering.