Table 1.

Overview of microbial macronutrient storage compounds with key references and characteristics.

Storage compound	Occurrence	Structure	Comments
Triacylglycerides (TAG) [139, 140] Hydrophobic lipids; as intracellular inclusions	Widespread in bacteria and fungi, not in archaea		High energy density, but can only be mobilized for energy under aerobic conditions
Polyhydroxyalkanoates (PHA) [141, 142] High molecular-weight, hydrophobic lipid; as intracellular inclusions	Bacteria and archaea, not in eukaryotes		Intracellular PHA can comprise >80% of cell dry weight; can only be mobilized for energy under aerobic conditions
Glycogen [143, 144] Hydrophilic, high molecular-weight polymer of glucose; as intracellular granules	Bacteria, fungi, animals, possibly archaea, not plants		Polymer enables glucose storage without increasing osmotic pressure
Trehalose [103, 145] Nonreducing water-soluble glucose dimer	Bacteria, archaea, fungi, plants, and invertebrates		Plays roles in osmotic regulation and protection against desiccation
Wax esters [140, 146] Hydrophobic lipid; as intracellular inclusions	Bacteria		Also in eukaryotes, e.g., in hydrophobic leaf cuticles, but not as storage
Polyphosphate [92, 147, 148] Storage of P and energy, as intracellular granules or in acidocalcisomes	Ubiquitous, but extent of accumulation differs		Multifunctional molecule also involved in pH buffering, heavy metal chelation, cell signaling, motility, and virulence
Cyanophycin [149, 150] Storage of N; as intracellular granules	Cyanobacteria, some other bacteria		Up to 18% of cell dry mass of cyanobacteria and >40% in Acinetobacter calcoaceticus

More details are provided in Supplementary Information 1.