The iModulon framework: how x-AI reveals microbial regulatory logic

The accelerating deposition of RNAseq data over the past decade has motivated the development of advanced transcriptomic data analytics that can operate on a large number of samples. One successful approach is to apply independent component analysis (ICA) to large prokaryotic transcriptomic compendia to decompose them into independently modulated gene sets, called iModulons. Here, we review the data science principles underlying ICA-based transcriptome decomposition, computational workflows that support its routine application, and iModulonDB infrastructure that hosts and disseminates the resulting decompositions. We present iModulonDB 3.0 that contains 53 species and 71 ICA decompositions across 33,062 RNA-seq samples, with several well-sampled species (e.g., Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa) represented by more than one compendium. With 71 standardized decompositions, we demonstrate systematic cross-species comparison of species-specific iModulon structures. This comparison identifies a shared "regulatory toolkit" of 13 modules conserved across distantly related bacteria, alongside a long tail of lineage-specific programs. We assess the design principles and limitations governing iModulon reconstruction and computation. Together, these advances position the iModulon framework as an accessible, community-driven approach for reading accumulating public transcriptomes as reusable regulatory programs, enabling biological discovery and module-level design in synthetic biology.