Exoproteome Remodeling by the BraI/R Quorum Sensing Circuit and Interspecies Competition in Paraburkholderia

Quorum sensing (QS) is a cell-to-cell communication mechanism that enables bacteria to coordinate collective behaviors in response to population density. The BraI/R QS system is conserved among Burkholderia and Paraburkholderia species, and its regulatory role is still unknown. In this study, the BraI/R QS of P. kururiensis was investigated for biological control of another bacterial species. The results demonstrate that the functional BraI/R system influences interbacterial competition, as braI and braR mutant strains failed to inhibit the growth of Escherichia coli, in contrast to the wild-type strain. These findings suggest that the BraI/R QS system plays a regulatory role in modulating interspecies antagonism. Comparative exoproteome analyses were performed for the wild-type and the BraI/R QS-mutant P. kururiensis strains, revealing distinct protein populations, including structural and effector proteins of the Type VI secretion system (T6SS). Genomic mapping revealed that two of those T6SS-proteins were encoded within a specific T6SS gene cluster (T6SS-3), while others originate outside any major T6SS gene cluster. The identification of exoproteome targets regulated by the BraI/R QS system represents a significant advance toward the understanding of the molecular mechanisms underpinning P. kururiensis interactions with competing bacteria, further supporting its potential as a biological control agent against phytopathogenic and/or free-living species.