Improved production of bacterial cellulose and its application potential

Abstract

Bacterial cellulose, produced by Acetobacter species, displays unique properties, including high mechanical strength, high water absorption capacity, high crystallinity, and an ultra-fine and highly pure fibre network structure. It is expected to be a new commodity biochemical with diverse applications, if its mass production process could be improved, especially via submerged fermentation technology. It has already found application as a food matrix (nata de coco) and as dietary fibre, as a temporary dressing to heal skin burns, as an acoustic or filter membrane, as ultra-strength paper and as a reticulated fine fibre network with coating, binding, thickening and suspending characteristics. A wet spinning process for producing textile fibres from bacterial cellulose has also been developed, and applications as a superconducting and optical fibre matrix are under study. We have been able to improve bacterial cellulose production in surface culture (up to 28 g/l), as well as in submerged culture (up to 9 g/l) via strain selection, mutation, medium composition optimization and physico-chemical fermentation parameter control. Glucose and fructose as the carbon source and acetic acid as the energy source, combined with a precise control of pH and dissolved oxygen levels, results in highly improved cellulose yields. An internal pH control in stationary surface cultures was achieved by an appropriate choice of the ratio of fructose/glucose/acetic acid. It was also demonstrated that cellulose formation could be enhanced by adding insoluble microparticles such as diatomaceous earth, silica, small glass beads and loam particles to submerged, agitated/aerated Acetobacter cultures. This microcarrier-enhanced cellulose synthesis could be the result of the formation of microenvironments with locally lowered dissolved oxygen levels because of the attachment of Acetobacter cells as a biofilm on the particles. As such, less glucose is lost as gluconate, saving it for cellulose formation and maintaining the pH profile within the desirable range. We have also developed a UV-mutation and proton enrichment strategy, which allows the selection of A. xylinum mutants, which are highly restricted in (keto)gluconate synthesis and produce cellulose more efficiently, even under oxidative culture conditions. Combining these nutritional, genetic and bioprocess-technological improvements, very high levels of bacterial cellulose have been attained. Further improvements are needed to arrive at an economical fermentation process for mass production of bacterial cellulose.