What organisms are responsible for breaking down compost?

The compostable, living material is broken down in compost bins and piles by the meeting of proper levels of air, moisture, and temperature; and to the regular turning over of the pile. Added to the proper environment is the role of microorganisms, and of macroorganismssuch as ground beetles. And there may be the introduction of composting worms. Any and all of these factors contribute to the decomposition of compostable materials into dark brown, fresh-smelling, organic matter-rich soil.