Microorganisms are the most abundant and diverse organisms on Earth. They live in communities that are capable of degrading complex molecules, and can be harnessed for the treatment of wastewater or the production of biogas. To exploit the full capabilities of microbial communities we must first understand how microbes interact with each other. A particularly important interaction for ecosystem stability is mutualism, which is a positive interaction that benefits all participating members. During my PhD project, we will apply omics approaches to study Moorella thermoacetica strains growing on C-1 compounds, together with a methanogenic partner (Methanothermobacter thermoautotrophicus). The aim is to uncover the molecular mechanisms behind this mutualistic interaction and its evolution.