INBALANCE investigated how interactions between bacteria and benthic invertebrates regulate nitrogen (N) cycling in shallow estuarine sediments. While bacteria are traditionally considered the main drivers of the N cycle, the project demonstrated that ecological interactions with meio- and macrofauna play a crucial role in shaping nitrogen transformations. INBALANCE quantified the importance of these interactions, focusing on the identity and activity of bacteria associated with benthic invertebrate hosts, the most abundant functional group in estuarine systems. The project explored a spectrum of associations—from strict symbioses to casual interactions—to reveal their contribution to nitrogen cycling and overall ecosystem functioning.