UC Davis

Microbial cells and the derivative structures have the potential to efficiently encapsulate, protect and controlled release a diversity of bioactive and liable compounds. The cell carriers with unique structural and compositional properties could potentially possess functional properties such as binding with target sites and transforming the compounds in situ. Whilst extensive studies have been carried out to develop synthetic and chemical encapsulation carriers, the natural microbial structures have had limited applications as microcarriers. The primary goal of this study is to evaluate the encapsulation and delivery functionalities of cell carriers. Yeast cells, yeast cell wall particles (YCWPs) and bacterial cells were selected as model microcarriers. Encapsulation of model phenolic compounds was carried out using an established pressure-assisted technology. Overall, we hypothesize that the cell-based carriers are able to encapsulate and effectively protect diverse profiles of bioactive chemicals and bind to target delivery sites. In addition, live cells will transform the encapsulated compounds with the intrinsic metabolic activities and deliver the functional metabolites in situ. In order to characterize the encapsulation and delivery of model bioactive compounds using cell carriers and explore their ex-vivo binding properties with target biological sites, yeast cells and YCWPs were applied as model microcarriers, and pathogenic biofilms and dermal tissue were used as model delivery sites. Scanning electron microscopy was employed to study the cell structural integrity after encapsulation. Confocal laser scanning microscopy and in-vivo fluorescence macro-imaging were applied to visualize the cellular localization of encapsulated substances and the binding affinity between the microcarrier and the target sites respectively. Quantitative understandings of the encapsulation efficiency, antimicrobial performance and transdermal delivery were furthered with spectrophotometry coupled with microbiological protocols and HPLC analysis. To understand the cell carriers’ encapsulation of complex mixtures of compounds from crude materials, bacterial cells were selected as the model cell carrier to encapsulate phytochemicals from plant juices. Oxidative stability of encapsulated compounds under thermal treatment has also been monitored over time and measured using spectrophotometry. In addition, this study also evaluated a novel delivery mechanism using live cell carriers. The viability and metabolomic response of cell carriers after encapsulation, transformation of the target compound and delivery of produced metabolites were elucidated using liquid chromatography coupled with tandem mass spectrometry. The results of this study demonstrated that the cell carriers can bind to target cells and tissues such as pathogenic biofilms and skin surfaces, which facilitated the antimicrobial treatment and transdermal delivery of bioactive compounds. The microcarriers were able to encapsulate complex profiles of phenolic compounds and protect the compounds against degradation from heat and oxidation for an extended period of time. Moreover, live cell carriers were able to maintain viability after the encapsulation process and produce target metabolites from encapsulated compounds with deranged metabolic activities. In summary, the results of this research demonstrated that cell-based carriers are a promising class of new emerging microencapsulation systems with a wide range of applications. Furthermore, the project was the first to investigate live cell carriers as an active encapsulation and delivery system that can transform target substances in situ. Future studies could further the development of novel cell-based encapsulation carriers with enhanced functionalities and target modifications leveraging the unique and intrinsic properties of microorganism.