PHAaccumulating

PHA-accumulating organisms are microorganisms that store polyhydroxyalkanoates (PHAs) as intracellular granules, typically under conditions of carbon surplus with limitation of other nutrients such as nitrogen or phosphorus. This strategy provides a reversible carbon and energy reserve that supports survival during periods of stress. The term is used to describe diverse bacteria and some archaea capable of producing and maintaining PHA inclusions.

PHAs are biodegradable polyesters composed of hydroxyalkanoate monomers. The most common homopolymer is polyhydroxybutyrate (PHB), while copolymers such as polyhydroxybutyrate-co-valerate (PHBV) offer varied material properties. In cells, PHAs accumulate as granules surrounded by surface-associated proteins, including phasins, which help regulate granule size and stability. The core biosynthetic pathway involves three key enzymes: PhaA (β-ketothiolase) condenses acetyl-CoA, PhaB (acetoacetyl-CoA reductase) reduces the intermediate, and PhaC (PHA synthase) polymerizes the hydroxyalkanoate units into PHAs. When carbon becomes limited or energy is needed, PHA depolymerases such as PhaZ mobilize stored polymer back into usable substrates.

Industry and ecology: PHA-accumulating bacteria are central to bioplastic research and production. PHAs are biodegradable and biocompatible, making them attractive as sustainable alternatives to conventional plastics. Industrial processes seek to optimize yields, tailor monomer composition, and utilize waste streams as carbon sources. Ecologically, PHA accumulation occurs in soils, sediments, wastewater systems, and various aquatic environments, reflecting a widespread strategy for carbon storage and stress resilience in microbial communities.