Microorganisms are ubiquitous on Earth and contribute significantly to global biogeochemical cycles, human health and biotechnological processes. Microbial population sizes and structures are governed by resource availability and lifestyle strategies of constituent taxa. Therefore, microbial community structures mainly develop in response to environmental conditions (i.e., resource gradient) and respective niche breadths (i.e. range of usable resources) of constituent populations. To date, microbial niche breadths within environments are poorly understood. The current project LEGeLiS (short for Linking Environment – Genome – Lifestyle Strategy) aims at testing two hypotheses derived from ecological theory: (i) an environment characterised by fluctuating conditions selects for organisms with a different lifestyle strategy than a more stable environment and (ii) a generalist population is more constrained in terms of genetic variation than a specialist population. If these two hypotheses hold true when tested in different environments, we would have a clear evidence that environmental conditions are indeed significant in determining population-level genetic variations frequency. We recently developed a methodology for the concomitant extraction of DNA, RNA, proteins and metabolites from a unique sample followed by their multi-omic analyses as well as a suitable bioinformatic workflow. In this project, we will for the first time, apply these methods on time series samples derived from wastewater, anaerobic digesters and human gut environments. These three model systems were chosen based on their distinct frequency of environmental fluctuations. Detailed understanding of the link between microbe lifestyle strategy and environmental conditions will allow to devise ecosystematic community-wide control strategies leading to a range of different biotechnological and biomedical applications in the future.