Tight coupling of polymerization and depolymerization of polyhydroxyalkanoates ensures efficient management of carbon resources in Pseudomonas putida

Authors

  • Sagrario Arias,

    Corresponding author
    • Environmental Microbiology Laboratory, Helmholtz Centre for Infection Research, Braunschweig, Germany
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    • These authors have equally contributed to this work.
  • Monica Bassas-Galia,

    1. Environmental Microbiology Laboratory, Helmholtz Centre for Infection Research, Braunschweig, Germany
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    • These authors have equally contributed to this work.
  • Gabriella Molinari,

    1. Environmental Microbiology Laboratory, Helmholtz Centre for Infection Research, Braunschweig, Germany
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  • Kenneth N. Timmis

    1. Environmental Microbiology Laboratory, Helmholtz Centre for Infection Research, Braunschweig, Germany
    2. Institute for Microbiology, Technical University Braunschweig, Braunschweig, Germany
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  • Funding Information The presented study arose from a larger project within the scope of a patent value fund. In this context we acknowledge the financial support by the Dritte Patentportfolio Beteiligungsgesellschaft mbH & Co. KG (Germany) and the overall project coordination provided by Clou Partners (Germany).

For correspondence. E-mail sagrario.arias-rivas@helmholtz-hzi.de; Tel. (+49) 531 6181 4030; Fax (+49) 531 6181 4199.

Summary

Environmental microbes oscillate between feast and famine and need to carefully manage utilization, storage and conversion of reserve products to exploitable sources of carbon and energy. Polyhydroxyalkanoates (PHAs) are storage polymers that serve bacteria as sources of food materials under physiological conditions of carbon demand. In order to obtain insights into the role of PHA depolymerase (PhaZ) and its relationship to a PHA polymerase (PhaC2) in the carbon management activity of Pseudomonas putida strain U, we created a polymerase hyperexpression strain and a depolymerase knockout mutant of this strain, and examined their synthesis of PHA and expression of their PHA genes. This study revealed that hyperexpression of PhaC2 led to the accumulation of higher amounts of PHA (44%wt) than in the wild-type strain (24%wt) after 24 h of cultivation, which then returned to wild-type levels by 48 h, as a result of elevated depolymerization. The phaZ mutant, however, accumulated higher levels of PHA than the parental strain (62%wt), which were maintained for at least 96 h. Transcriptional analysis of the pha cluster by RT-PCR revealed that PHA operon proteins, including depolymerase, are expressed from the beginning of the growth phase. Hyperexpression of the PhaC2 polymerase was accompanied by an increase in the expression of the PhaZ depolymerase and a decrease in expression of another PHA polymerase, PhaC1. This suggests tight regulatory coupling of PHA polymerase and depolymerase activities that act in synergy, and in concert with other PHA proteins, to provide dynamic PHA granule synthesis and remodelling that rapidly and sensitively respond to changes in availability of carbon and the physiological-metabolic needs of the cell, to ensure optimal carbon resource management.

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