Unprecedented climate change, pollutants and habitat alterations are causing abiotic stress across all plants and animals. Global increases in temperature, as well as decreases in pH in the ocean, have already caused microbiome dysbiosis in a range of species, and previously commensal microbes have turned pathogenic in response to extreme environmental conditions. This will have far-reaching consequences for host survival and associated ecosystem functions. However, host microbiomes may actually be the key to buffering these unprecedented environmental changes. The host microbiome contains massive genetic potential, and their vast numbers, high turnover, wide metabolic scope and short generation times may afford opportunities for faster acclimatisation and adaptation. Examples of this already exist, although responses are likely to be highly context-dependent. It is becoming increasingly clear that preservation of the microbiome is likely to be the key to maintaining healthy ecosystems in an uncertain future. However, there are still large knowledge gaps in almost every area, which need to be urgently addressed so we can apply conservation efforts in a judicious manner.

A classic example of microbiome function is its role in nutrient assimilation in both plants and animals, but other less obvious roles are becoming more apparent, particularly in terms of driving infectious and non-infectious disease outcomes and influencing host behaviour. However, numerous biotic and abiotic factors influence the composition of these communities, and host microbiomes can be susceptible to environmental change. How microbial communities will be altered by, and mitigate, the rapid environmental change we can expect in the next few decades remain to be seen. That said, given the enormous range of functional diversity conferred by microbes, there is currently something of a revolution in microbial bioengineering and biotechnology in order to address real-world problems including human and wildlife disease and crop and biofuel production. All of these concepts are explored in further detail throughout the book.