The quorum sensing system of Novosphingobium sp. ERN07 regulates aggregate formation that promotes cyanobacterial growth

Microbial aggregates play key roles in cyanobacterial blooms. Being a bacterial communication mechanism, quorum sensing (QS) synchronizes gene expression in a density-dependent manner and regulates bacterial physiological be-havior. However, the regulatory role of QS in the formation of cyanobacteria-associated bacterial aggregates remains poorly understood. Here, we present insight into the role of QS in regulating bacterial aggregate formation in a repre-sentative bacterial strain, Novosphingobium sp. ERN07, which was isolated from Microcystis blooms in Lake Taihu. A biosensor assay showed that ERN07 exhibits significant AHL-producing capacity. Biochemical and microscopic anal-ysis revealed that this strain possesses the ability to form aggregated communities. Gene knockout experiments indi-cated that the AHL-mediated QS system positively regulates bacterial aggregation. The aggregated communities possess the ability to enhance the production of extracellular polymeric substances (EPS), alter EPS composition ratios, and affect biofilm formation. The addition of aggregated substances also has a significant growth-promoting effect on M. aeruginosa. Transcriptomic analysis revealed that the aggregated substances positively regulate photosynthetic ef-ficiency and energy metabolism of M. aeruginosa. These findings show that QS can mediate the aggregation phenotype and associated substrate spectrum composition, contributing to a better understanding of microalgal-bacterial interac-tions and mechanisms of Microcystis bloom maintenance in the natural environment.

Automated summary

Microbial aggregates, regulated by quorum sensing (QS), play a significant role in cyanobacterial blooms. This study reveals the role of QS in regulating bacterial aggregate formation and its effects on microalgal-bacterial interactions and maintenance of Microcystis blooms in the natural environment.