All organisms interact with their environments, whether acquiring the resources needed for survival, sensing other organisms or physical surfaces, protecting themselves from various threats, or disposing of their waste products. With their high biomass and large populations worldwide, microorganisms interact with their nonliving and living environments to have effects that extend far beyond their individual cells, even at the global scale. These interactions also shape the microbes themselves, physically and physiologically, through genetic and epigenetic processes. (Epigenetic processes, in contrast to genetic processes, involve changes in gene expression that are not due to changes in DNA sequence.)