10.1.1 Microorganisms and microenvironment In a microbial ecosystem individual cells grow to form populations Metabolically related populations constitute groupings called guilds Sets of guilds conducting complementary physiological processes interact to form microbial communities Microbial communities then interact with communities of macroorganisms to define the entire ecosystem10.1.1 Microorganisms and microenvironment Metabolically related populations constitute groupings called guilds. Sets of guilds conducting complementary physiological processes interact to form microbial communities. In a microbial ecosystem individual cells grow to form populations. Microbial communities then interact with communities of macroorganisms to define the entire ecosystem