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Exopolysaccharide production by different marine bacteria species and Enterobacter A47
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This thesis is focused on the production of bacterial exopolysaccharides (EPS) using a Schatz medium, supplemented with yeast extract and peptone, and glucose as carbon source.
Production assays were carried out in shake flasks with different marine bacteria, of the genera Pseudoalteromonas and Psychrobacter, and with the bacterium Enterobacter A47. In order to optimize EPS production, the strains were chosen to proceed with bioreactor assays. The marine bacteria were able to produce 1.33-1.91 g.L-1 of EPS, corresponding to volumetric productivities of 0.67-0.96 gEPS.L-1.d-1. On the other hand, Enterobacter A47 was able to synthesize 1.81 g.L-1 of EPS, corresponding to a volumetric productivity of 0.91 gEPS.L-1.d-1. The exopolysaccharides produced by marine bacteria were mainly composed of glucose, while the one produced by Enterobacter A47 was similar to the fucose rich exopolysaccharide – FucoPol – typically produced by this culture.
In order to optimize EPS production by Enterobacter A47 in salt conditions, the impact of NaCl (0-40 g.L-1), yeast extract (0-4 g.L-1) and peptone (0-2 g.L-1) concentrations on cellular growth and EPS production was studied. Statistical tools, such as response surface methodology and central composite rotatable design, were used. The results showed that Enterobacter A47 has the ability to grow and synthesize EPS under most of the experimental conditions tested. The optimal NaCl, yeast extract and peptone concentrations were determined to be 8.1 g.L-1, 0.8 g.L-1 and 0.4 g.L-1, respectively.
Afterwards, the impact of pH on EPS production, as well as on the polymer´s composition, by Enterobacter A47 was also evaluated. It was found that the use of the modified Schatz medium and pH control at 7.0 led to an increase in EPS production (3.49 g.L-1), corresponding to a volumetric productivity of 1.75 gEPS.L-1.d-1. It was also observed that the decrease from pH 7.0 to pH 6.0 had little effect on EPS production (3.33 g.L-1), whereas at pH 8.0 a significant reduction in EPS synthesis (0.79 g.L-1) was observed. The exopolysaccharides produced were rich in fucose.
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Exopolysaccharides Schatz medium Marine bacteria Enterobacter A47 Response surface methodology Impact of pH