The simultaneous production of microbial polymers levan and poly[3-hydroxybutyrate] (PHB), a type of polyhydroxyalkanoates, was investigated in this work. The study involved the fermentation of sucrose and molasses by H. smyrnensis AAD6T (BAE2 strain) to produce PHB (intracellular) and levan (extracellular). Both polymers were isolated and characterized by FTIR. Levan was also characterized by thin-layer chromatography (TLC) and viscosimetric analysis. The amount of biomass was 25 g until the end of fermentation. The PHB rate was 0.015 g in both media and the average PHB productivity was 6.0 x 10-4 g PHB/g biomass. The highest rate of levan was 9 g/L in the range of 72–80 h, in the molasses-based medium. The FTIR spectra showed specific signals for each of the polymers, such as the peak at 1700 for the carbonyl group of esters for the PHB and signals at 900 and 800, which are typical signals for levan fructose rings. Furthermore, acid hydrolysis of levan revealed that it was formed only by fructose, as confirmed by TLC With this study, H. smyrnensis AAD6T BAE2 co-produced PHB and levan using a low-cost carbon source, showing great potential in reducing biopolymer manufacturing costs.
The sequential production of polyhydroxyalkanoates (PHA) and levan was investigated by microbial fermentation using agro-industrial residues. PHA production was carried out by Cupriavidus necator DSMZ 545 in two steps: a) bacterial growth, using pure (MN) and hydrolyzed (MH) molasses and; b) accumulation of PHA, using standard glycerol (GP) and crude glycerol (GB). The fermented remaining from the C. necator growth stage was separated from the PHA-containing biomass and used in the subsequent production of levan by Bacillus subtilis (natto) Takahashi. The medium containing MH+GP generated a rate of 15 mg of PHA, while the medium based on MH+GB the rate of PHA was almost twice as high (28.4 mg). FTIR spectroscopic analysis of PHA indicated stretching vibrations characteristic for a PHB-like molecule. In turn, the levan produced in this study was precipitated with different volumes of ethanol, generating levans with different molecular weights. The results of the characterization of this fructan by chromatography showed that it was predominantly constituted by fructose units. In addition, the dynamic and kinematic viscosity values for levan were similar in the analyzed concentrations and, therefore, did not provide any clues about the molecular weight of this biopolymer. Finally, the sequential production process of PHA and levan, as a second bioproduct, represents an elegant alternative to reduce the total costs of PHA production.
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