Sandhu, Armaan KaurFischer, Brady R.Subramanian, SenthilHoppe, Adam D.Brözel, Volker Siegfried2025-05-082025-05-082025-03Sandhu, A.K., Fischer, B.R., Subramanian, S. et al. 2025, 'Self-growth suppression in Bradyrhizobium diazoefficiens is caused by a diffusible antagonist', ISME Communications, vol. 5, no. 1, art. ycaf032, doi : 10.1093/ismeco/ycaf032.2730-6151 (online)10.1093/ismeco/ycaf032http://hdl.handle.net/2263/102332DATA AVAILABILITY : All the data generated for analysis during this study are included in this published article and its supplementary information files.Microbes in soil navigate interactions by recognizing kin, forming social groups, exhibiting antagonistic behavior, and engaging in competitive kin rivalry. Here, we investigated a novel phenomenon of self-growth suppression (sibling rivalry) observed in Bradyrhizobium diazoefficiens USDA 110. Swimming colonies of USDA 110 developed a distinct demarcation line and inter-colony zone when inoculated adjacent to each other. In addition to self, USDA 110 suppressed growth of other Bradyrhizobium strains and several other soil bacteria. We demonstrated that the phenomenon of sibling rivalry is due to growth suppression but not cell death. The cells in the inter-colony zone were culturable but had reduced respiratory activity, ATP levels, and motility. The observed growth suppression was due to the presence of a diffusible effector compound. This effector was labile, preventing extraction, and identification, but it is unlikely a protein or a strong acid or base. This counterintuitive phenomenon of self-growth suppression suggests a strategic adaptation for conserving energy and resources in competitive soil environments. Bradyrhizobium’s utilization of antagonism including self-growth suppression likely provides a competitive advantage for long-term success in soil ecosystems.en© The Author(s) 2025. Published by Oxford University Press on behalf of the International Society for Microbial Ecology. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/).Bradyrhizobium diazoefficiensAntagonismKin rivalrySibling rivalrySelf-growth suppressionArticle