All living organisms depend on the supply of necessary elements
from the Earth. Since the Earth is a closed system with a finite
supply of essential elements such as hydrogen (H), oxygen (O),
carbon (C), nitrogen (N), sulfur (S) and phosphorus (P), recycling
of these elements is fundamental to avoid exhaustion. Microbes
are critical in the process of breaking down and transforming dead
organic material into forms that can be reused by other organisms.
This is why the microbial enzyme systems involved are viewed as
key ‘engines’ that drive the Earth’s biogeochemical cycles.1