PrintMicroorganisms are everywhere in the Earth surface environment. Their presence has significant influence in the natural and engineered environments. They play a key role in the biogeochemical cycling of elements such as carbon (C), oxygen (O) and nitrogen (N). For example, primary production involves photosynthetic microorganisms that transform CO2 in the atmosphere into organic (cellular) materials of vegetation in terrestrial systems. Planktonic algae and cyanobacteria on the other hand, are the “grass of the sea”. They account for ~ 50% of the primary production on the planet and are the primary carbon source for marine life. The fixation of N from the N2 gas also occurs through N-fixing microorganisms. Microorganisms are believed to be critical in the origin of life and in the transformation of rocks to soils that create life-accommodating environments on Earth. In the modern time when humans generated large quantities of waste and contaminants, microorganisms have overtaken the daunting tasks of cleaning up and recycling wastes in engineered systems such as wastewater treatment plants. They have also been indispensable in remediating contaminated water, soils, and aquifers.