This article deals with the articulation between different professional cultures, required for the implementation of extreme citizen science projects, and the necessary role of digital and open infrastructures in this respect. It draws on a project carried out between 2018 and 2020, called PLACES, which enabled the implementation, observation, and analysis of three participatory research projects involving journalists and social scientists. In the first part of the article, we will start by presenting the experimental framework set up within the PLACES project, and its results. We will present the strengths and obstacles of the researcher-journalist collaborations we observed; then we will highlight the importance of helping participants of a collaborative project to develop close links in their daily professional activities. In the second part, we will discuss the role of open digital infrastructures, with a particular focus on two research-society services. We will stress their value in supporting these collaborations, not only for letting participants produce common outputs (written or not), but also in understanding the challenges they face in sharing knowledge among their respective professional worlds.