Priority research questions in microbiome-integrated urban design.

Urbanization is accelerating at an unprecedented pace, with 70% of the global population projected to live in cities by 2050. This shift presents significant challenges and opportunities for fostering sustainable urban ecosystems aligned with the United Nations Sustainable Development Goals. Microbiomes-the diverse communities of microorganisms that underpin ecosystem function-are increasingly recognized for their vital role in nutrient cycling, climate regulation, biodiversity support, and human well-being. However, their consideration and integration in urban design remain underexplored, often limited to disease mitigation. The emerging field of microbiome-integrated urban design seeks to leverage microbial activity to enhance urban health and resilience through a multispecies framework. To address critical gaps, the Probiotic Cities Working Group convened a global interdisciplinary workshop, engaging experts from ecology, architecture, urban planning, immunology, and social sciences. Using reverse brainstorming and thematic analysis, participants identified eight core themes and 40 priority research questions (via a modified Delphi technique). These themes span communication and policy, pollution prevention, interdisciplinary collaboration, experimental design, ethics, and public perception of microbiomes. A binomial concordance analysis revealed strong consensus on the top-ranked questions, which address urgent needs such as improving science communication, defining success metrics, and promoting evidence-based microbiome interventions. This paper discusses the top-ranked priority research questions and their broader implications for microbiome science, urban health, and sustainable development. By focusing on these priorities, researchers, policymakers, and practitioners can foster a transformative agenda to integrate microbiomes into urban design, advancing resilient and equitable cities for the future.