PHAproducing

PHA-producing describes organisms or systems that synthesize polyhydroxyalkanoates (PHAs), a family of intracellular polyester storage polymers produced by many bacteria and some archaea. PHAs accumulate as granules in the cytoplasm when cells experience excess carbon and simultaneous limitation of essential nutrients such as nitrogen, phosphorus, or sulfur. The most common polymer is polyhydroxybutyrate (PHB); copolymers such as polyhydroxybutyrate-co-valerate (PHBV) broaden material properties and applications.

Biochemically, PHAs are produced from acetyl-CoA or related intermediates by a sequence of enzymes—PhaA, PhaB, and PhaC. PhaA (β-ketothiolase) condenses substrates, PhaB reduces them, and PhaC (PHA synthase) polymerizes hydroxyalkanoate monomers into intracellular granules. The granules are stabilized by proteins such as phasins (PhaP). PHA mobilization occurs through depolymerases (PhaZ) when carbon becomes limiting or cells need energy. Synthesis is tightly regulated by carbon flux and nutrient availability.

Common PHA producers include Cupriavidus necator (formerly Ralstonia eutropha), Alcaligenes spp., various Bacillus and Pseudomonas species. Production can utilize diverse feedstocks, including sugars, fatty acids, plant oils, and waste streams. Industrial processes often employ a two-stage strategy: an initial growth phase followed by a carbon-rich accumulation phase to maximize polymer yield.

PHAs are biocompatible and biodegradable, with material properties similar to some petrochemical plastics, making them attractive for packaging, disposable items, and certain medical devices. Challenges include production cost and downstream recovery from cells; research continues in metabolic engineering and non-solvent extraction methods to improve viability.