Formation of Isoprenoids

Isoprenoids, also known as terpenoids, are a diverse group of metabolites produced in all free-living organisms. They play an indispensable role in a wide variety of essential processes but also contribute to a better adaptation to the environment in the form of specialized secondary metabolites. In spite of their notable structural and functional diversity, all isoprenoids are synthesized from the same metabolic precursors, which are then converted into prenyl diphosphates of increasing length. Such basic prenyl diphosphate intermediates represent the starting point of downstream pathways leading to the formation of the vast diversity of end products. Here we present an overview of isoprenoid biosynthesis in microbes from the three kingdoms of life, namely, bacteria, archaea, and eukaryotic microorganisms (mainly microalgae and yeast), with a special emphasis on the research conducted during the last decade. We also discuss the main functional classes of isoprenoids occurring in these microorganisms by focusing in the representative model organisms of each kingdom. Finally, we examine key research needs in this field. This includes expanding our understanding of secondary isoprenoid metabolism in microbes, examining the evolutionary relationships between the two core biosynthetic pathways and improving our ability to engineer production of industrially useful isoprenoids in microbes.