Integrative metabolomics and proteomics allow the global intracellular characterization of Bacillus subtilis cells and spores.

Reliable and comprehensive multi-omics analysis is essential for researchers to understand and explore complex biological systems more completely. Bacillus subtilis is a model organism for Gram-positive spore-forming bacteria, and in-depth insight into the physiology and molecular basis of spore formation and germination in this organism requires advanced multilayer molecular datasets generated from the same sample. In this study, we evaluated two monophasic methods for polar and nonpolar compound extraction (acetonitrile/methanol/water; isopropanol/water, and 60% ethanol), and two biphasic methods (chloroform/methanol/water, and methyl tert-butyl ether/methanol/water) on coefficients of variation of analytes, identified metabolite composition and the quality of proteomics profiles. The analytical workflow comprises (1) parallel metabolite and protein extraction, (2) monophasic or biphasic sample extraction, (3) proteomics comparison and (4) multi-omics-based data visualization. The 60% EtOH protocol proved to be the easiest in sample processing and more amenable to automation. Collectively, we annotated 505 and 484 metabolites and identified 1665 and 1562 proteins in B. subtilis vegetative cells and spores, respectively. We also show differences between vegetative cells and spores from a multi-omics perspective and demonstrated that an integrative multi-omics analysis can be implemented from one sample using the 60% EtOH protocol. Correlation analysis further demonstrated that the metabolome and proteome datasets were highly correlated in content for components annotated to be part of the pyrimidine metabolism pathway. The results obtained by the 60% EtOH protocol provide a comprehensive insight into differences in the metabolic and protein makeup of B. subtilis vegetative cells and spores.