Bacterial medium-chain-length PHA synthesis and mobilization

A reusable bacterial module for production and intracellular turnover of medium-chain-length poly(3-hydroxyalkanoate) storage polyester. The required core begins with an externally supplied (R)-3-hydroxyacyl-CoA pool: class II PhaC enzymes polymerize these monomers at PHA granules, and intracellular PhaZ depolymerases remobilize stored polymer. PhaG-dependent routing from de novo fatty-acid synthesis is an optional upstream submodule whose physiological chemistry is not fixed here. Beta-oxidation-derived monomer supply and phasin-mediated granule organization are adjacent processes outside the core reaction boundary.

PhaC1 and PhaC2 are represented as members of one class II synthase family, not as sequential steps. The core module is complete from an (R)-3-hydroxyacyl-CoA input boundary through polymerization and mobilization. PhaG is optional upstream context because beta-oxidation and other routes can independently provide PhaC substrates; its in vivo chemistry is deliberately not asserted as a single direct ACP:CoA reaction. The PhaG annoton therefore records a routing role without assigning substrates, products, or a module-level catalytic function. A thioesterase-plus-ligase model implicating PP_0763 remains plausible but is not promoted to a required step without direct native-context resolution. PhaC1 and PhaC2 are co-exemplars of one class II synthase role; neither is labeled primary, redundant, or substrate-specialized. PhaF, PhaI, and PhaD affect granule architecture or regulation but do not define additional reaction steps in this module.