Microstructure of Gel Films of Bacterial Cellulose Synthesized under Static Conditions of Cultivation of the Gluconacetobacter hansenii GH-1/2008 Strain on Nutrient Media with Different Carbon Sources

The study presents a comparative analysis of the structures of dried films of bacterial cellulose (BC) produced by bacteria of the Gluconacetobacter hansenii GH-1/2008 strain under static conditions of cultivation on nutrient media with different carbon sources, such as glucose, sucrose, maltose, fructose, and lactose. It was found that the supramolecular structure of the films is a three-dimensional network composed of orientationally ordered microfibrils with an average diameter from 30 to 60 nm, which consist of crystalline and amorphous regions. An analysis of the powder X-ray diffraction patterns demonstrated that the crystalline regions of microfibrils are formed by cellulose I. Depending on the composition of the nutrient medium, the degree of crystallinity of the films varies in the range from similar to 20 to 90%. It was found that, regardless of the carbon source, the top and bottom surfaces of BC films have different microstructures defined by static conditions of cultivation. Thus, the top surface of gel films contains pores with a diameter of up to 500 nm, whereas a wider pore size distribution (up to 600 nm) is observed on the bottom surface. The difference between the average pore sizes on the top and bottom surfaces varies from 95 to 180 nm and from 100 to 200 nm, respectively. The measurements of the mechanical properties of the films showed that the films produced by the cultivation on media containing fructose and sucrose have the maximum strength, whereas the films produced using lactose and maltose have the minimum strength. The data on the BC productivity of the GH-1/2008 strain were obtained.