In situ modification of bacterial cellulose by adding diverse substances during the fermentation of Komagataeibacter xylinus

Abstract

Bacterial cellulose (BC) has garnered much interest as a biopolymer to replace synthetic plastics. BC is a biomaterial similar in chemical structure to wood but is composed of pure chains of glucose and contains none of the other carbohydrates that wood is composed of. Sustainable alternatives to synthetic plastics are a necessity but even in the field of BC there are many methods that use ecologically damaging substances to functionalise it. In this thesis we showcase several methods to modify BC in a sustainable and ecological manner. We utilise a one pot methodology where the modification of the BC must occur in as few steps as possible with no post production modification. In the silanation study we investigate the use of in situ bioprocessing for the production and surface modification BC with silicon additives. The surface properties and tensile strength of the BC were studied and compared with plain BC. The effect the modification exhibited on the survivability of the bacteria was assessed by optical density measurements and found that the addition of the modification marginally slowed growth in the case of tetramethyl orthosilicate (TMOS) and did not affect the growth in the case of tetraethyl orthosilicate (TEOS). Characterisation of the modified BC was carried out using FTIR, EDX and confirmed the presence of silicon in the material. The width of fibres in the microstructure of BC was measured using SEM. Two different silicon modifications were used to modify the BC, it was shown that the TMOS modification decreased the tensile strength but that the TEOS increased the tensile strength of the BC fibres compared to plain BC. In addition, we found that the washing conditions of 1% NaOH (w/v), industrial methylated spirit (IMS), and deionised water (DI) showed some impact on the properties of the samples, particularly the IMS produced a reduced contact angle in the modified samples. However, the contact angle increased in the case of TEOS modification with the NaOH wash. In chapter three we showcase a one-pot method for acetylating BC by replacing the glucose traditionally used in media with N-acetyl glucosamine (NAG) with the aim of modifying the tensile properties, increasing hydrophobicity and introducing functional groups for potential chemical modification. We demonstrate that this method can produce a structurally homogenous form of BC with a more homogeneous and consistent tensile strength compared to plain BC. Additionally, the water contact angle (CA) was also improved over plain BC with the NAG resulting in CA exceeding 90 ° and retaining a greater contact angle after 1 minute compared to plain BC controls. Furthermore, we analysed the metabolic profile of Komagataeibacter xylinus during the formation of BC to provide information on the mechanism by which NAG is incorporated into BC. We characterised the material using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), and liquid chromatography mass spectroscopic analysis (LC/MS) to confidently confirm that the BC had been modified by the incorporation of NAG into the chemical structure of BC. Chapter four describes a similar methodology to that in chapter threeutilising azide modified glucose. It was shown that the reaction between an azide and 1-hexyne was successful indicating that the reaction with azide glucose would also be successful. The culturing with azide glucose did not produce an azide modified pellicle during fermentation. To deduce why FTIR analysis was performed on the growth media before and after culturing. It was found that the azide glucose was not taken up by the K. xylinus. With further analysis it was deduced that this was due to the porins present in the bacteria being unable to transport the azide glucose across the cell wall. Chapter five describes a methodology to utilise silicon precipitating proteins to coat BC in silica nanoparticles. The silica precipitating proteins would be produced by BL21 and added to the culture media during formation of the pellicle alongside the silicates that would be converted to the nanoparticles. This would allow full coverage of silica nanoparticles as well as incorporation of the nanoparticles into the cross section of the BC. This study demonstrates that the feasibility of a functional one pot modification of BC by altering the media composition of K. xylinus and suggests potential for further optimisation of these methodologies to enhance the functionality of BC.

Date of Award	30 Apr 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	Yunhong Jiang (Supervisor), Meng Zhang (Supervisor) & Valery Kozhevnikov (Supervisor)