Bacterial cellulose culture medium

Tarr and Hibbert13 published the first detailed study of the formation of bacterial cellulose. A systematic series of experiments, conducted with a view to obtaining a culture medium which did not support visible growth of A. xylinum until a suitable source of carbon was added, indicated that a solution (pH 5.0) containing 0.1% asparagine, 0.5% potassium dihydrogen phosphate, 0.1% sodium chloride and 0.5% ethanol satisfied these requirements. Maximum polysaccharide formation oc-... 

Oince cellulose is insoluble high polymers under physiological condi- tions, cellulase which is destined to attack it has been expected to be an extracellular enzyme. In fact, most of cellulolytic microorganisms secrete some cellulase components into the culture medium, and almost all work on the cellulase have been performed using these extracellular components. In the cultures of cellulolytic bacteria, cellulases are not only found in their culture filtrates, but also are generally obtainable from the cells by treatment with autolytic agents—e.g., toluene (9, 19, 30). These facts indicate that at least certain components are existent within the bacterial cells and that their physiological function may be distinct from that of the extracellular components. 

BC is pure cellulose made by bacterial fabrication via biochemical steps and self-assembling of the secreted cellulose fibrils in the medium. Shaping of BC materials in the culture medium can be controlled by the type of cultivation and kind of bioreactor and then it obtained BC hydrogel or BC in dry state by methods like freeze-drying [1]. 

Seifert, M., Hesse, S., Kabrelian, V., Klemm, D. Controlling the water content of never dried and reswollen bacterial cellulose by the addition of water-soluble polymers to the culture medium. J. Polym. Sci. Part A Polym. Chem. 42(3), 463-470 (2004)... 

The more suitable purification method for the bacterial cellulose calls upon distilled water, sodium hydroxide and sodium hypochlorite solutions, since it guarantees the elimination of bacteria cells and culture medium residues from the membrane. For clinical applications, the suitable sterilization processes are gamma radiation and ethylene oxide treatment, but the latter should be avoided for bacterial cellulose dry or wet membrane, because it can cause allergic reactions, mostly when used internally. 

The structural characteristics of bacterial cellulose are directly related to two factors, namely (1) the origin of the strain, which determines the la/ip ratio and (2) the culture medium composition that influences the chain size. Such characteristics determine the degree of crystallinity of bacterial cellulose and consequently, their physicochemical properties. Structural modifications can be accomplished in a post-production step, since it is possible to functionalize the hydroxyl groups (—OH) by methylation [13], esterification [14], sulphonation [13], nitration [13], deoxyamination [15], etc. 

In addition to plant-derived cellulose, cellulose can also be synthesised by bacteria such as from the Acetobacter species. By culturing cellulose-producing bacteria in the presence of natural fibres in an appropriate culture medium, bacterial cellulose is preferentially deposited in situ onto the surface of natural fibres. The introduction of bacterial cellulose onto natural fibres provides new means of controlling the interaction between natural fibres and polymer matrices. Coating of natural fibres with bacterial cellulose not only facilitates good distribution of bacterial cellulose within the matrix, but also results in an improved interfacial adhesion between the fibres and the matrix. This enhances the interaction between the natural fibres and the polymer matrix through mechanical interlocking. 

Another purpose of adding chemicals to the culture medium is the chemical modification of the structural and physical properties of bacterial cellulose, allowing the preparation of composites directly during biosynthesis and broadening the applications of cellulose [18], as will be discussed latter. 

Figure 2.2 Photographs of a static culture (with a visible BC pellicle in the interface air-culture medium) and a purified bacterial cellulose wet membrane produced in static conditions. Reproduced with permission from [29, 39].

Due to the biological nature of bacterial cellulose, in-situ methods involving the inclusion a polymer in the culture medium for cellulose to combine the materials provides an alternative method for creating composites. It is possible that composites could be made simply by the inclusion of the host polymer in the mediiun, however the development of subsequent treatments, for example the hot pressing of the starch/cellulose films described above, could improve the contact and interactions between the two materials. Identifying materials to be used in composites with bacterial cellulose in this way could provide improvements into the development of these types of composites. 

Cellulose is synthesized by a wide variety of aerobic bacterial genera such as aceto-bacter, acrobacter, rizobium and so on. However, the reasons for the synthesis of cellulose by bacteria, independent of the genera, are not clearly known and a plausible mechanism has been understood. It has been hypothesized that bacteria produces cellulose in order to maintain their spatial position at the interface of air-culture medium so that it can take oxygen from the air and nutrients from the culture medium for... 

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