Pseudomonas sp. 14-3, a strain that accumulates large quantities of polyhydroxybutyrate (PHB) when grown on octanoate, was isolated from Antarctic environments. This isolate was characterized on the basis of phenotypic features and partial sequencing of its 16S ribosomal RNA gene. Pseudomonas sp. 14-3 showed increased tolerance to both thermal and oxidative stress compared with three other Pseudomonas species. Stress tolerance of Pseudomonas sp. 14-3 was analyzed in polyhydroxyalkanoate accumulating and non-accumulating conditions, and increased levels of stress resistance were observed when PHB was produced. Pseudomonas sp. 14-3 was isolated from Antarctic regions, a habitat normally exposed to extreme conditions. An association between high PHB accumulation and high stress resistance in bacteria adapted to extreme environments is suggested.
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.
arcA codes for a central regulator in Escherichia coli that responds to redox conditions of growth. Mutations in this gene, originally named dye, confer sensitivity to toluidine blue and other redox dyes. However, the molecular basis for the dye-sensitive phenotype has not been elucidated. In this work, we show that toluidine blue redirects electrons to O2 and causes an increase in the generation of reactive O2 species (ROS). We also demonstrate that synthesis of poly (3-hydroxybutyrate) suppresses the Dye phenotype in E. coli recombinants, as the capacity to synthesize the polymer reduces sensitivity to toluidine blue, O2 consumption and ROS production levels.
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