Stearate Liquid Marbles for Bacterial Cellulose Production: Influence of the Liquid Marble Interface on Bacterial Cellulose Properties

We report aerobic bacteria culture performed in liquid marbles (LMs) for bacterial cellulose (BC) production. LMs are droplets stabilized by coating an aqueous solution with hydrophobic particles, which allow vapor and gas transfer through the liquid core–hydrophobic particle interface. We used safe food-grade stearate microparticles for LM formation. An LM containing an aerobic acetic acid bacterium, Komagataeibacter xylinus (K. xylinus), which produces BC, was successfully prepared by dropping a culture medium solution inoculated with the bacteria onto a calcium stearate powder layer and rolling it to full coverage by calcium stearate microparticles. After the LMs containing the cells were statically cultured, the core solution became a hydrogel due to the production of BC by the cells. The obtained hydrogel (LM–BC gel) had a higher water holding capacity than that prepared by using a conventional test tube or Erlenmeyer flask. Scanning electron microscopy (SEM) observations showed that the BC fibers on the surface of the LM–BC gel were thicker than those prepared in conventional systems and formed a network structure with large holes, which was different from the conventional BC structure. We found that the BC prepared in LMs had the characteristic structure only on the outer surface of the gel. Considering that the bacterium movement is driven by the inverse force of the secretion of cellulose fibers, we found that the cells in the vicinity of the LM interface moved differently compared to that in conventional culture systems. The amount of BC produced per LM was linearly proportional to the core volume of the LM. In addition, changing the core volume significantly affected the surface area to volume ratio (A/V), whereas it did not affect the amount of BC produced per culture medium volume. Thus, the stearate LM system allows the production of BC by aerobic acetic acid bacteria, and the LM interface plays a critical role in the produced BC properties.