A non-hypothesis-driven practical laboratory activity on functional metagenomics: "fishing" protein-coding DNA sequences from microbiomes.

Practical laboratory of the most functional metagenomics courses focuses on activities aimed at providing specific skills in bioinformatics through the analysis of genomic datasets. However, sequence-based analyses of metagenomes should be complemented by function-based analyses, to provide evidential knowledge of gene function. A "true" functional metagenomic approach relies on the construction and screening of metagenomic libraries - physical libraries that contain DNA cloned from metagenomes of various origin. The information obtained from functional metagenomics will help in future annotations of gene function and serve as a complement to sequence-based metagenomics. Here, we describe a simple protocol for the construction of a metagenomic DNA library, optimized and tested by a team of undergraduate biotechnology students. This protocol is based on a technique developed in our laboratory and currently used for research. Using this protocol, libraries of protein domains can be quickly generated, from the DNA of any intron-less genome, such as those of bacteria or phages. Therefore, these libraries provide a valuable platform for training students in various validation tools, including computational methods - for example, metagenome assembly, functional annotation - and proteomics techniques, including protein expression and analysis. By varying the biological source and validation pipeline, this approach offers virtually limitless opportunities for innovative thesis research projects.