Poly(3-hydroxybutyrate) hyperproduction by a global nitrogen regulator NtrB mutant strain of Paracoccus denitrificans PD1222

Abstract

Paracoccus denitrificans PD1222 accumulates short-length polyhydroxyalkanoates, poly(3-hydroxybutyrate), under nitrogen-deficient conditions. Polyhydroxybutyrate metabolism requires the 3-ketoacyl-CoA thiolase PhaA, the acetoacetyl-CoA dehydrogenase/reductase PhaB and the synthase PhaC for polymerization. Additionally, P. denitrificans PD1222 grows aerobically with nitrate as sole nitrogen source. Nitrate assimilation is controlled negatively by ammonium through the two-component NtrBC system. NtrB is a sensor kinase that autophosphorylates a histidine residue under low-nitrogen concentrations and, in turn, transfers a phosphoryl group to an aspartate residue of the response regulator NtrC protein, which acts as a transcriptional activator of the P. denitrificans PD1222 nasABGHC genes. The P. denitrificans PD1222 NtrB mutant was unable to use nitrate efficiently as nitrogen source when compared to the wild-type strain, and it also overproduced poly(3-hydroxybutyrate). Acetyl-CoA concentration in the P. denitrificans PD1222 NtrB mutant strain was higher than in the wild-type strain. The expression of the phaC gene was also increased in the NtrB mutant when compared to the wild-type strain. These results suggest that accumulation of poly(3-hydroxybutyrate) in the NtrB mutant strain of PD1222 responds to the high levels of acetyl-CoA that accumulate in the cytoplasm as consequence of its inability to efficiently use nitrate as nitrogen source.

Sea-Ice Bacteria Halomonas sp. Strain 363 and Paracoccus sp. Strain 392 Produce Multiple Types of Poly-3-Hydroxyalkaonoic Acid (PHA) Storage Polymers at Low Temperature

“…392 two gene clusters ( phaRPCZ and phaAB ) were identified ( Fig. 1 ), in accordance with a previous study ( 37 ).…”

“…PHBV production in Paracoccus spp. has also been observed in previous studies ( 53 , 54 ), although they are better known as a PHB producers ( 6 , 37 ).…”

Imaging and modelling of poly(3-hydroxybutyrate) synthesis in Paracoccus denitrificans

“…This results in the depletion of the cellular pool of acetyl-CoA, which in turn causes a strong decrease in the rate of acetoacetyl-CoA synthesis by beta-ketothiolase ( phaA ). The same correlation between PHB accumulation and acetyl-CoA concentration was also observed by Olaya-Abril et al ( 2018 ) in a mutant strain with increased PHB accumulation. The stoichiometry of beta-ketothiolase involving 2 acetyl-CoA molecules is likely to make its rate more sensitive to decreased acetyl-CoA concentrations (if the concentrations are below the enzyme saturation levels).…”

Imaging and modelling of poly(3-hydroxybutyrate) synthesis in Paracoccus denitrificans

“…This results in the depletion of the cellular pool of acetyl-CoA, which in turn causes a strong decrease in the rate of acetoacetyl-CoA synthesis by beta-ketothiolase (phaA). The same correlation between PHB accumulation and acetyl-CoA concentration was also observed by Olaya-Abril et al (2018) in a mutant strain with increased PHB accumulation. The stoichiometry of beta-ketothiolase involving 2 acetyl-CoA molecules is likely to make its rate more sensitive to decreased acetyl-CoA concentrations (if the concentrations are below the enzyme saturation levels).…”