Current and emerging in vitro and in vivo biofilm models in investigating fungal-bacterial polymicrobial communities

The concept of microbial biofilms revolutionised the scientific approaches towards understanding and manipulating the biology of microorganisms. With the diversity of microbiome and the complexities of ecological niches, biofilms in their natural habitats often consist of a variety of species, genera, and kingdoms. Such polymicrobial biofilms have been modelled, both in vitro and in vivo, not only to establish biofilm-specific microbial paradigms such as communal interactions, quorum sensing and antimicrobial resistance mechanisms, but also to define their relationships with the host and neighbouring environment. While each biofilm model has its own pros and cons, they play a quintessential role in the advancement of current knowledge on microbial communal lifestyle and their applications. Thus far, biofilm models have been predominantly developed, tested, and validated for investigating single species biofilms or those that are formed by polymicrobial communities from a single kingdom. The models specified for interkingdom biofilms are relatively rare. This chapter discusses some of these in vitro and in vivo systems that have been designed and successfully tested for modelling interkingdom biofilms formed by fungi and bacteria, their applications, limitations, and potential for further optimisations.