Photoheterotrophic Assimilation of Valerate and Associated Polyhydroxyalkanoate Production by Rhodospirillum rubrum

Abstract

<jats:p>Purple non-sulfur bacteria are increasingly regarded for industrial applications in bioplastics, pigment and biomass production. In order to optimize the yield of future biotechnological processes, the assimilation of different carbon sources by <jats:italic>Rhodospirillum rubrum</jats:italic> (<jats:italic>Rs. rubrum</jats:italic>) has to be understood. As they are released from several fermentation processes, volatile fatty acids (VFAs) represent a promising carbon source in the development of circular industrial applications. To obtain an exhaustive characterization of the photoheterotrophic metabolism of <jats:italic>Rs. rubrum</jats:italic> in the presence of valerate, we combined phenotypic, proteomic and genomic approaches. We obtained evidence that valerate is cleaved into acetyl-CoA and propionyl-CoA and depends on the presence of bicarbonate ions. Genomic and enzyme inhibition data showed that a functional methylmalonyl-CoA pathway is essential. Our proteomic data showed that the photoheterotrophic assimilation of valerate induces an intracellular redox stress which is accompanied by an increased abundance of phasins (the main proteins present in PHA granules). Finally, we observed a significant increase in the production of the copolymer P(HB-co-HV) presenting an outstanding (more than 80%) percentage of HV monomer. Moreover, an increase in the PHA content was obtained when bicarbonate ions were progressively added to the medium. The experimental conditions used in this study suggest that the redox imbalance is responsible for PHA production. These findings also reinforce the idea that PNSB are suitable for PHA production through another strategy than the well-known feast and famine process.</jats:p> <jats:p><jats:bold>Importance</jats:bold> The use and the littering of plastics represent major issues that humanity has to face. Polyhydroxyalkanoates (PHAs) are good candidates for the replacement of oil-based plastics as they exhibit comparable physicochemical properties but are biobased and biodegradable. However, the current industrial production of PHAs is curbed by the production costs, which are mainly linked to the carbon source. Volatile fatty acids issued from the fermentation processes constitute interesting carbon sources as they are cheap and easily available. Among them, valerate is gaining interest regarding the ability of many bacteria to produce a copolymer of PHAs. Here, we describe the photoheterotrophic assimilation of valerate by <jats:italic>Rhodospirillum rubrum,</jats:italic> a purple non-sulfur bacterium mainly known for its metabolic versatility. Using a knowledge based optimization process, we display a new strategy for the improvement of PHA production, paving the way for the use of <jats:italic>Rhodospirillum rubrum</jats:italic> in industrial processes.</jats:p>

Integrated sustainable process for polyhydroxyalkanoates production from lignocellulosic waste by purple phototrophic bacteria

“…Lower Y PHA on the control tests was obtained (10%), which responds to the excess of nutrients in the synthetic medium, as PHA production is enhanced when growth is limited (Brandl et al, 1991). On the measurement taken at the end of the experiment, on the stationary phase, a slightly reduced Y PHA was noticed: 16%, 16%, and 14%, which may be related to the consumption of PHA for maintaining the redox balance, as has been recently suggested (Bayon‐Vicente, Zarbo, et al, 2020). Therefore, the analysis of the mechanisms of PHA accumulation is critical to elucidate the process performance.…”

“…Thereby, it is associated with growth. A maximum of PHA accumulation is therefore expected before reaching the stationary stage (Bayon‐Vicente, Wattiez, et al, 2020; Bayon‐Vicente, Zarbo, et al, 2020; Fradinho et al, 2013). A more extensive and comprehensive description of the process can be found in the supplementary material.…”

High‐Yield Production, Characterization, and Functionalization of Recombinant Magnetosomes in the Synthetic Bacterium Rhodospirillum rubrum “magneticum”

“…15-1, [35] the phototrophic alphaproteobacterium Rhodospirillum rubrum has been efficiently endowed with the ability of magnetite biomineralization. [36] R. rubrum is relatively closely related to M. gryphiswaldense [37][38][39] with a 16S rRNA similarity of 90%, [36] and has gained increasing relevance in the field of biotechnology, for example, as production host for polyhydroxyalkanoates [40,41] or for hydrogen production. [42,43] The step-wise transfer of the five major magnetosome operons mamAB op , mamGFDC op , mms6 op , mamXY op , and feoAB1 of M. gryphiswaldense enabled the biosynthesis of magnetosome-like magnetite particles within the resulting transgenic strain R. rubrum ABG6X_feoAB1 (in the following, referred to as R. rubrum "magneticum").…”

Effects of Mixing Volatile Fatty Acids as Carbon Sources on Rhodospirillum rubrum Carbon Metabolism and Redox Balance Mechanisms

“…The production of hydroxybutyrate or hydroxyvalerate from propionate results in consumption of the redox equivalent; however, when production occurs from butyrate, PHA synthesis cannot play the role of an electron sink. It was hypothesized that under butyrate conditions, the PHA production can be used as a buffer zone to regulate the production of the reduced equivalent, making PHA synthesis a possible redox balance mechanism [ 19 , 40 ]. We recently linked the presence of propionate to a low level of PHA accumulation [ 20 ].…”