Fecha de publicación: 2007.
Polyhydroxyalkanoates (PHAs) are accumulated as intracellular granules by many bacteria under unfavorable conditions, enhancing their fitness and stress resistance. Poly(3-hydroxybutyrate) (PHB) is the most widespread and best-known PHA. Apart from the genes that catalyze polymer biosynthesis, natural PHA producers have several genes for proteins involved in granule formation and/or with regulatory functions, such as phasins, that have been shown to affect polymer synthesis. This study evaluates the effect of PhaP, a phasin, on bacterial growth and PHB accumulation from glycerol in bioreactor cultures of recombinant Escherichia coli carrying phaBAC from Azotobacter sp. strain FA8. Cells expressing phaP grew more, and accumulated more PHB, both using glucose and using glycerol as carbon sources. When cultures were grown in a bioreactor using glycerol, PhaP-bearing cells produced more polymer (2.6 times) and more biomass (1.9 times) than did those without the phasin. The effect of this protein on growth promotion and polymer accumulation is expected to be even greater in high-density cultures, such as those used in the industrial production of the polymer. The recombinant strain presented in this work has been successfully used for the production of PHB from glycerol in bioreactor studies, allowing the production of 7.9 g/liter of the polymer in a semisynthetic medium in 48-h batch cultures. The development of bacterial strains that can efficiently use this substrate can help to make the industrial production of PHAs economically feasible. Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Afiliación de los autores: De Almeida, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Afiliación de los autores: Pettinari, M.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Palabras claves: Bacteria; Biomass; Bioreactors; Biosynthesis; Escherichia coli; Glycerol; Intracellular granules; Polyhydroxyalkanoates (PHAs); Semisynthetic medium; Stress resistance; Proteins; bacterial protein; carbon; glucose; glycerol; poly(3 hydroxybutyric acid); polyhydroxyalkanoic acid; polymer; regulator protein; bacterium; fitness; gene; growth; polymer; protein; stress resistance; article; Azotobacter; bacterial growth; bacterial strain; bacterium culture; bioreactor; biosynthesis; catalysis; cell granule; controlled study; Escherichia coli; nonhuman; protein expression; protein function; stress; Azotobacter; Bacterial Proteins; Biomass; Bioreactors; DNA-Binding Proteins; Escherichia coli; Fermentation; Glucose; Glycerol; Hydroxybutyrates; Polyesters; Azotobacter; Bacteria (microorganisms); Escherichia coli.
Repositorio: Biblioteca Digital (UBA-FCEN). Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales
Fecha de publicación: 2001.
Pseudomonas oleovorans GPo1 and its polyhydroxyalkanoic acid (PHA) depolymerization-minus mutant, GPo500 phaZ, residing in natural water microcosms, were utilized to asses the effect of PHA availability on survival and resistance to stress agents. The wild-type strain showed increased survival compared to the PHA depolymerase-minus strain. The appearance of a round cellular shape, characteristic of bacteria growing under starvation conditions, was delayed in the wild type in comparison to the mutant strain. Percent survival at the end of ethanol and heat challenges was always higher in GPo1 than in GPo500. Based on these results and on early experiments (H. Hippe, Arch. Mikrobiol. 56:248-277, 1967) that suggested an association of PHA utilization with respiration and oxidative phosphorylation, we investigated the association between PHA degradation and nucleotide accumulation. ATP and guanosine tetraphosphate (ppGpp) production was analyzed under culture conditions leading to PHA depolymerization. A rise in the ATP and ppGpp levels appeared concomitant with PHA degradation, while this phenomenon was not observed in the mutant strain unable to degrade the polymer. Complementation of the phaZ mutation restored the wild-type phenotype.
Afiliación de los autores: Ruiz, J.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Afiliación de los autores: Méndez, B.S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Palabras claves: adenosine triphosphate; guanosine 3' diphosphate 5' diphosphate; nucleotide; polyhydroxyalkanoic acid; article; bacterial growth; degradation; depolymerization; gene mutation; genetic complementation; nonhuman; oxidative phosphorylation; phenotype; Pseudomonas oleovorans; stress; survival; Biodegradation, Environmental; Carboxylic Ester Hydrolases; Culture Media; Ecosystem; Ethanol; Fresh Water; Heat; Mutation; Nucleotides; Polymers; Pseudomonas; Bacteria (microorganisms); Equidae; Negibacteria; Pseudomonas; Pseudomonas oleovorans.