Characterization of bacterial cellulose produced by Komagataeibacter xylinus strains grown in styrene/glucose mixtures

This study is focused on the characterization of bacterial cellulose (BC) produced by Komagataeibacter xylinus strains DSM 2325, DSM 2004, and DSM 46604 from styrene/glucose mixtures. Styrene, the aromatic monomer of petrochemical plastics such as polystyrene, served as a co-substrate for bacterial cultivation, being assimilated by all strains, although with differing efficiency for BC biosynthesis. The best performing strain was K. xylinus DSM 2325 with a BC production of 2.70 ± 0.4 g/L. Interestingly, K. xylinus DSM 2004 produced BC from styrene as the sole carbon source, yielding 0.32 ± 0.02 g/L BC. The presence of styrene in the cultivation media had a minor influence on the produced BC chemical structure, thermal degradation temperature (318–337 °C), and morphology, where compact fibers of diameters ranging from 31 to 47 nm were observed. The crystallinity index of the samples was obtained through X-ray diffraction and showed that values varied according to the medium used (41–33%). However, the membranes synthesized in the presence of styrene were thinner (3–22 μm) than those produced from glucose (12–44 μm) and had low gas permeability. K. xylinus DSM 2325 and DSM 2004 membranes had also low permeability for O2 (1.1–2.5 barrer) and CO2 (2.5–5.8 barrer), while those produced by K. xylinus DSM 46604 had a higher permeability to CO2 (42.3 barrer) together with low permeability to O2 (2.5 barrer). Moreover, BC produced by K. xylinus DSM 2325 with styrene as an additive showed the highest crystallinity among all strains and mediums (46%). These results show the feasibility of using styrene as an effective co-substrate in a sustainable approach for its valorisation into a value-added biopolymer, with the advantage of tuning BC properties according to the envisaged application, by selecting the appropriate producing strain and culture medium.