The microbiome as engineering tool: Manufacturing and trading between microorganisms.

The integration of microbial technologies within the framework of the water-energy nexus has been taking place for over a century, but these mixed microbial communities are considered hard to deal with 'black boxes'. Process steering is mainly based on avoiding process failure by monitoring conventional parameters, e.g., pH and temperature, which often leads to operation far below the intrinsic potential. Mixed microbial communities do not reflect a randomised individual mix, but an interacting microbiological entity. Advance monitoring to obtain effective engineering of the microbiome is achievable, and even crucial to obtain the desired performance and products. This can be achieved via a top-down or bottom-up approach. The top-down strategy is reflected in the microbial resource management concept that considers the microbial community as a well-structured network. This network can be monitored by means of molecular techniques that will allow the development of accurate and quick decision tools. In contrast, the bottom-up approach makes use of synthetic cultures that can be composed starting from defined axenic cultures, based on the requirements of the process under consideration. The success of both approaches depends on real-time monitoring and control. Of particular importance is the necessity to identify and characterise the key players in the process. These key players not only relate with the establishment of functional conversions, but also with the interaction between partner bacteria. This emphasises the importance of molecular (screening) techniques to obtain structural and functional insights, minimise energy input, and maximise product output by means of integrated microbiome processes.