Reducing the environmental impact of biogenic PHAs production using an enzymatic recovery strategy
Bioplastics, in particular polyhydroxyalcanoates (PHAs), are widely studied as biodegradable materials for substitution of oil derived polymers. However, their production at an industrial scale is still limited due to high production costs. In addition, industrial PHAs recovery needs the use of large volumes of organic solvent like chloroform, which is not convenient for environmental safety (Byrom, 1994). Bosco and Chiampo (2010) reported four ways to reduce these costs including new cheap substrates, new fermentative strategies, new recovery and purification steps, and new microorganisms for accumulation of high PHA concentrations.
Further Authors:
C. Rondel
C.E. Mercato-Romain
V. Dossat-Létisse
D. Lefebvre
In this context, sewage sludge can be considered as a source of renewable organic carbon and of diversified microorganisms for biogenic PHA production. In addition, sewage sludge may also provide lytic microorganisms that are of a great interest for PHAs recovery using new and safe extraction procedure..According to this objective, a new strategy for the recovery of intracellular PHAs using multiple hydrolytic activities secreted by thermophilic strains isolated from composting sludge is presented in this study. Sewage sludge was sampled in a municipal composting plant (Muret, France), during the thermophilic stage of the process. Bacterial strains were isolated by cultivating these samples at 65°C on plate count agar and 7 different strains could be isolated. Two of them, named a and B, were selected for their ability to grow on anaerobic digested sludge. Further characterization using API ZYM® (Biomérieux; France) of the a and B exocellular activities showed the presence of phosphatase, lipase and osidase activities, but no protease activity was detected. The lytic potential of the a and B exocellular enzymes was then tested on pure cultures of Cupriavidus necator (Aragao et al., 1996). After PHA accumulation due to nutrients limitation, these producers were submitted to an osmotic shock (successive incubation in a hypertonic and hypotonic solution) and incubated with the hydrolytic supernatants of strains A and B selected from compost (37 and 65°C, 30 min, 10 ml of supernatant/g of dry matter). The released PHAs were quantified by GC method after their mild extraction with chloroform. When using a and B supernatants, 81±2% and 99±2% of PHAs were recovered at 37°C, respectively. Increasing either the temperature or the supernatant/ culture medium ratio did not significantly improve the percentage of PHA recovery. Similar extraction conditions were applied to a multi-species culture incubated with B supernatant, but only 65±3% of PHAs could be extracted because of the presence of flocs which limit the access of the hydrolytic enzymes to the cells. A physical pre-treatment has thus to be considered to dissociate flocs and improve the cellular lysis. In conclusion, this study demonstrates that enzymatic recovery of biogenic PHAs from various producers can be performed using lytic bacteria selected from sewage sludge, providing thus interesting reduction of the environmental impacts of PHAs bioproduction. In addition, the selected lytic strains are also of great interest for general improvement of carbon bio-availability in various organic wastes and their valorisation as renewable carbon source.
| Copyright: | © European Compost Network ECN e.V. | |
| Quelle: | Orbit 2012 (Juni 2012) | |
| Seiten: | 9 | |
| Preis inkl. MwSt.: | € 0,00 | |
| Autor: | Pr Elisabeth Girbal-Neuhauser  | |
| Artikel weiterleiten | Artikel kostenfrei anzeigen | Artikel kommentieren |
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