Improved bacterial nanocellulose production by co-cultivation

Abstract

Bacterial cellulose has high degree of crystallinity, high purity, excellent water-binding properties and good shape retention advantages, compared to plant cellulose, and it has many potential applications in various industries. The gluconic acid, a by-product produced during BC production, can decrease the pH of cultivation that leads to low BC yield by Komagataeibacter xylinus. Thus, maintaining the pH of cultivation for BC production was important and urgent task. In this study, the Acinetobacter baylyi ADP1gcd was employed to co-cultivate with K. xylinus, which aimed to well control the pH suitable for BC production by consuming the gluconic acid accumulation during static cultivation. The K. xylinus engineered type (pABCD) and wild type (WT) was proved to be able to produce BC in MA/9 medium. And the pABCD produced 2-fold more BC production than that of WT in MA/9 medium after 5 days. pABCD and WT obtained lower BC productivity in MA/9 medium than that in HS medium. The effect of different concentration glucose addition for growth of pABCD and BC production was also investigated in this study. The highest BC production on 2% glucose addition was around 0.267 g/L produced by pABCD after 5 days cultivation in MA/9 medium, and followed by 5% glucose (0.266 g/L), 1% glucose (0.2 g/L), 3.5% glucose (0.167 g/L) and 0.5% glucose (0.133 g/L). So, the BC productivity of pABCD increased with the increasing of glucose concentration until 2% in MA/9 medium. Moreover, the effect of arabinose (1%) and initial inoculate volume for BC production was studied. The presence of arabinose (1%) was proved to be able to achieve an in-crease of BC biosynthesis in MA/9 medium by inducing overexpression of bcs operon in pABCD strains. It yielded 0.267 g/L BC, which was 2-fold higher than that of arabi-nose absence. And the initial inoculate volume (OD600=0.02 or 0.04) of pABCD has no significant effect on the final BC productivity in MA/9 medium. The maximum concentration of gluconic acid consumed by A. baylyi ADP1gcd was about 80 mM in MA/9 medium. It was demonstrated that A. baylyi ADP1gcd was able to utilize all gluconic acid accumulated in MA/9 medium supplemented with glucose (2%) after 5 days cultivation. Finally, the pH of co-cultivation was maintained at optimized range (5.0-7.0), compared to that of pABCD pure cultivation group (below 4.0). However, the co-cultivation with and without 50 ug/ml chloramphenicol addition, yield approximately 0.267 g/L and 0.1667 g/L BC after 5 days cultivation, respectively, which was much less than that of pABCD pure cultivation group. The A. baylyi ADP1gcd helped in eliminating the gluconic acid and maintaining pH, but the glucose consumption was lower in co-cultivation than in pABCD pure cultivation. This phenomenon is interesting and will be a subject of future study.