Taxonomic implications of synthesis of poly-beta-hydroxybutyrate and other poly-beta-hydroxyalkanoates by aerobic pseudomonads

This study examines poly-β-hydroxybutyrate (PHB) and poly-β-hydroxyalkanoates (PHAs) production in Pseudomonas species to clarify their taxonomic implications. While PHB production is rare in most Pseudomonas species, medium-chain-length PHAs (mcl-PHAs) are commonly synthesized by fluorescent and non-fluorescent pseudomonads. The authors re-examined two species previously reported to produce PHB: Pseudomonas corrugata and Pseudomonas ficuserectae. Using gas chromatography analysis, they demonstrated that both species actually accumulate mcl-PHAs containing C6, C8, and C10 monomer units, not PHB. In contrast, Pseudomonas pseudoalcaligenes confirmed PHB synthesis as a control. The findings reveal that contrary to original descriptions, P. corrugata and P. ficuserectae do not synthesize PHB. The authors conclude that the inability to accumulate PHB by the majority of Pseudomonas species remains taxonomically valuable for genus-level differentiation. When polymer granules are observed, identifying constituent monomer units through controlled growth conditions and various carbon sources would enhance taxonomic classification of aerobic pseudomonads.

Key findings

• Pseudomonas corrugata and Pseudomonas ficuserectae synthesize medium-chain-length PHAs (mcl-PHAs) with C6, C8, and C10 monomers, not PHB as originally reported
• Most Pseudomonas species lack PHB synthesis capability, making this a valuable negative characteristic for taxonomic differentiation at the genus level
• mcl-PHA synthesis is a common feature of pseudomonads, particularly when grown on fatty acids, whereas PHB synthesis is rare in this genus
• Biochemical confirmation of polymer monomer composition using gas chromatography is essential for accurate taxonomic classification, as PHB and mcl-PHA granules cannot be visually differentiated by microscopy alone