Polyhydroxyalkanoates are essential for maintenance of redox state in the Antarctic bacterium Pseudomonas sp. 14-3 during low temperature adaptation

Abstract

Polyhydroxyalkanoates (PHAs) are highly reduced bacterial storage compounds that increase fitness in changing environments. We have previously shown that phaRBAC genes from the Antarctic bacterium Pseudomonas sp. 14-3 are located in a genomic island containing other genes probably related with its adaptability to cold environments. In this paper, Pseudomonas sp. 14-3 and its PHA synthase-minus mutant (phaC) were used to asses the effect of PHA accumulation on the adaptability to cold conditions. The phaC mutant was unable to grow at 10 degrees C and was more susceptible to freezing than its parent strain. PHA was necessary for the development of the oxidative stress response induced by cold treatment. Addition of reduced compounds cystine and gluthathione suppressed the cold sensitive phenotype of the phaC mutant. Cold shock produced very rapid degradation of PHA in the wild type strain. The NADH/NAD ratio and NADPH content, estimated by diamide sensitivity, decreased strongly in the mutant after cold shock while only minor changes were observed in the wild type. Accordingly, the level of lipid peroxidation in the mutant strain was 25-fold higher after temperature downshift. We propose that PHA metabolism modulates the availability of reducing equivalents, contributing to alleviate the oxidative stress produced by low temperature.

Life in the Cold: Proteomics of the Antarctic Bacterium Pseudoalteromonas haloplanktis

“…The genome of P. haloplanktis also reveals several insights into ROS protection such as deletion of ROS producing pathways, several occurrences of dioxygenases and the repair mechanisms of oxidized compounds (Medigue et al, 2005). Similar observations have been made in the genome and proteome of other psychrophilic microorganisms (Rabus et al, 2004;Medigue et al, 2005;Methe et al, 2005;Duchaud et al, 2007;Bakermans et al, 2007;Ayub et al, 2009;Piette et al, 2010), revealing a general constraint on these bacteria. However, we found that at 18 °C, another type of oxidative stress is induced by stimulation of metabolic activity.…”

“…On the other hand, the second group of proteins that displays the highest repression factors at 4 °C is represented by the oxidative stress-related proteins catalase (-6.5x), glutathione reductase (-8.1x) and peroxiredoxin (-15.7x). At first sight, this may be regarded as a conflicting result because conclusive evidences have indicated that psychrophiles are exposed to a permanent oxidative stress at low temperatures, which originates from improved dioxygen solubility and increased ROS stability (Rabus et al, 2004;Medigue et al, 2005;Methe et al, 2005;Duchaud et al, 2007;Bakermans et al, 2007;Ayub et al, 2009;Piette et al, 2010). In order to reconcile these apparent contradictions, it should be recalled that the general aerobic metabolism of the Antarctic bacterium is stimulated at 18 °C, also resulting in ROS production.…”

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

“…Consequently, lipid peroxidation in the mutant strain was 25-fold higher after decrease of temperature. Hence, PHA metabolism controls the availability of the reducing equivalents NADH and NADPH, thus alleviating the oxidative stress caused by cold temperature, by supplying the reductive power necessary to subdue the oxidative stress induced by cold conditions via PHB degradation [89].…”

Anr, the anaerobic global regulator, modulates the redox state and oxidative stress resistance in Pseudomonas extremaustralis

“…This species shows high stress resistance and is able to synthesize large amounts of poly(3-hydroxybutyrate), the best-known member of a bacterial reserve polymers family known as polyhydroxyalkanoates (PHAs) (Ayub et al, 2004(Ayub et al, , 2009. PHAs are involved in bacterial survival under different stressful conditions (Ló pez et al, 1995;Kadouri et al, 2005).…”