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2020-11-04 - Colloque/Présentation - communication orale - Anglais - page(s)

Bayon-Vicente Guillaume , Cabecas-Segura Paloma , Wattiez Ruddy , Leroy Baptiste , "Impact of carbon source and light intensity on the production of PHA by Rs. rubrum" in MELiSSA conference 2020, online, 2020

  • Codes CREF : Biochimie (DI3112), Biologie (DI3100), Microbiologie et protistologie [bacteriol.,virolog.,mycolog.] (DI3130)
  • Unités de recherche UMONS : Protéomie et Microbiologie (S828)
  • Instituts UMONS : Institut des Biosciences (Biosciences)
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Abstract(s) :

(Anglais) 1. Introduction Rhodospirillum rubrum is a purple non-sulphur bacterium (PNSB) belonging to the α-proteobacteria group well-known for its metabolic versatility. This metabolic versatility leads Rs. rubrum to the forefront of the stage in the biotechnological field and as a reference organism for the study of photosynthesis and assimilation of different carbon sources [1]. Among those carbon sources, volatile fatty acids (VFAs) are extensively studied in the biotechnology field due to their cheapness. PHAs are a family of polyesters seen as potential future plastic material synthesised by a wide variety of bacteria through the fermentation of sugars, lipids, alkanes, alkenes and alkanoic acids. These compounds are encapsulated in intracellular granules. Once extracted, PHAs exhibit thermoplastic and elastomeric properties close from petroleum based plastics and could be excellent replacements for them (i. e. good processability, physical characteristic and biodegradability). Whereas polyhydroxybutyrate (PHB) are stiff, brittle and shows high degree of crystallinity, polyhydroxybutyrate-co-hydroxyvalerate (P(HB-co-HV)) are flexible and possess low crystallinity, tensile strength and high melting point [2], [3]. Physiologically, PHAs are used as carbon or energy storage inclusions when lack of a nutrient (N, S, P) impairs bacteria growth. However, in our case, PHA production by Rhodospirillum rubrum is not induced by the lack of nutrient but more by a unbalanced redox state as it has been observed in Synechocystis PCC6803 [4] (Fig. 1 and 2). 2. Aim of the study The aim of this study is to understand the PHA production observed in Rhodospirillum rubrum S1H. The understanding of the parameters inducing the PHA production could allow the increase of PHA content and industrial yield. 3. Material and methods Bacteria were cultivated in presence of valeric acid or in presence of acetic acid supplemented with either 3 or 50 mM NaHCO3-. Growth of bacteria submitted to 50 µmol photons/m² s was followed through optical density at a wavelength of 680 nm (OD680nm). Rhodospirillum rubrum was cultivated under anaerobic phototrophic conditions. PHA were extracted following the protocol of Snell et al., 2002 [5] with some modifications. Briefly, pellets resulting from 500µl of culture were suspended in 500 µl of chloroform and 2 mL of a solution of methanol:concentrated HCl (90:10; v:v) were added. The solution was incubated during 2 hours at 100°C. After cooling, 2mL of distilled water were added and the chloroform phase was submitted to GC-MS. 4. Results The investigation of the PHA content in presence of valeric acid revealed the production of the high added value compound poly(hydroxybutyrate-co-hydroxyvalerate) with a high monomeric percentage of 3-hydroxyvalerate. Indeed, in all valeric acid conditions tested, 3-hydrovaleric monomer reached at least 80%. Moreover, the total PHA content was higher in the condition where the bicarbonate ions were added progressively than in the condition where bicarbonate ions were supplemented in excess (Fig. 3). The cultivation of Rhodospirillum rubrum in presence of acetic acid revealed the accumulation of copolymers containing only a few percentage of hydroxyvalerate monomer. The culture of the acetate competent strain (a strain exhibiting outstanding ability to assimilate acetic acid) in the same condition, revealed higher percentage of hydroxyvalerate in PHA produced. It is interesting to notice than the increase of light intensity from 50 to 150 µmol photons is linked to the increase of PHA content (Fig. 4). 5. Conclusion Our hypothesis concerning the link between the PHA production and the intracellular redox imbalance seems to be right indicating that destabilising the redox ratio by removing NaHCO3 from the environment or increase the light intensity can increase PHA production by Rhodospirillum rubrum.