Exopolysaccharide production by the marine bacterium Alteromonas macleodii Mo169 using fruit pulp waste as the sole carbon source

Abstract

A sugar-rich apple pulp waste generated from fruit processing for juice production was used as the sole carbon source for the cultivation of Alteromonas macleodii Mo169, a marine bacterium known for its EPS-secreting ability. The strain efficiently utilized the glucose and fructose present in the apple pulp waste, reaching biomass and EPS production of 9.20 ± 0.61 and 3.51 ± 0.08 g L−1, respectively, in 24-hour bioreactor cultivation. Two high molecular weight (Mw) fractions (1.7 ± 0.0 and 0.74 ± 0.0 MDa) were detected in the sample recovered from the cell-free supernatant by dialysis. The compositional analysis revealed the presence of glucose (31.1 ± 0.2 mol%), arabinose (23.9 ± 0.1 mol%), mannose (17.3 ± 0.1 mol%), glucosamine (10.3 ± 0.5 mol%), galactose (8.7 ± 0.0 mol%) and galacturonic acid (8.7 ± 0.0 mol%), as well as a high content in sulphate (6.0 ± 0.5 wt%). Given the presence of a high Mw polysaccharide in the apple pulp waste, probably pectin, a fraction of the detected sugar monomers might be attributed to that polymer, which was recovered together with A. macleodii Mo169 EPS. Concomitant with EPS synthesis, there was a viscosity build-up in the cultivation broth, which developed a shear-thinning fluid behaviour not observed in the initial medium. Therefore, this study demonstrates that apple pulp waste can be efficiently converted into a novel polysaccharide by A. macleodii Mo169 in a sustainable bioprocess. Moreover, the EPS sugar and acyl composition, together with its good thickening capacity, render the biopolymer of interest for use in several applications.