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Microbial Bioplastics Production and Degradation

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Front. Bioeng. Biotechnol. | doi: 10.3389/fbioe.2019.00059

Multiple nutrient-limited growth and polyhydroxybutyrate (PHB) production of Rhodospirillum rubrum on syngas is restricted by the availability of CO as energy source

Stephanie Karmann1, 2, Sven Panke2 and  Manfred Zinn1*
  • 1Institute of Life Technologies, HES-SO Valais-Wallis, Switzerland
  • 2Department of Biosystems Science and Engineering, ETH Zürich, Switzerland

Syngas from gasified organic waste materials is a promising feedstock for the biotechnological synthesis of the bioplastic poly([R]-3-hydroxybutyrate) (PHB) with Rhodospirillum rubrum.
In a first approach, growth studies were carried out with this strain in gas-tight serum vials. When syngas (40% CO, 40% H2, 10% CO2, 10% N2 v/v) was diluted with N2 to 60%, a 4 times higher biomass production was detected than for samples grown on 100% syngas, thus indicating a growth inhibitory effect. The best performing syngas-mixture was then used for C-, C,N- and C,P-limited fed-batch fermentations in a bioreactor with continuous syngas and acetate supply. It was found that C,P-limited PHB productivity was 5 times higher than for only C-limited growth and reached a maximal PHB content of 30% w/w. Surprisingly, growth and PHB production stopped when N, as a second nutrient, became growth-limiting. Finally, it was concluded that a minimal supply of 0.2 g CO g-1 biomass h-1 has to be guaranteed in order to cover the cellular maintenance energy.

Keywords: Rhodospirillum rubrum, syngas, Fed-batch, Poly(3-hydroxybutyrate) (PHB), multiple nutrient-limited growth

Received: 13 Sep 2018; Accepted: 05 Mar 2019.

Edited by:

Subba Rao Chaganti, University of Windsor, Canada

Reviewed by:

Christopher Nomura, SUNY College of Environmental Science and Forestry, United States
Antonio Marzocchella, Department of Chemical Engineering , Materials and Industrial Production, Polytechnic and Basic Sciences School, University of Naples Federico II, Italy  

Copyright: © 2019 Karmann, Panke and Zinn. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Manfred Zinn, HES-SO Valais-Wallis, Institute of Life Technologies, Sion, CH-9014, Switzerland, manfred.zinn@hevs.ch