The quorum-sensing TraI/TraR system contributes to the release of Fe and Al from biotite by Agrobacterium pusense SX41

Abstract

The quorum-sensing (QS) system in Rhizobiaceae has been studied, however, the mechanisms of QS system-mediated mineral dissolution by bacteria remain poorly understood. Here, the mineral-solubilizing Agrobacterium pusense SX41 harboring the QS system (responsible for N-acyl homoserine lactone (AHL) production) was characterized for QS system-mediated Al and Fe release from biotite. Whole-genome sequence analysis revealed that SX41 contains the QS TraI/TraR system. SX41 and the SX41∆traI, SX41∆traR, and SX41∆traI/R mutants were constructed from SX41 and compared for QS TraI/R system-mediated Fe and Al release from biotite in the solution and the underlying mechanisms. The SX41∆traI, SX41∆traR, and SX41∆traI/R mutants significantly decreased the Al and Fe concentrations in the medium by 24 % to 54 % on day 1 and 25 % to 42 % on day 5, while these mutants significantly reduced exopolysaccharide (EPS) concentrations in the medium by 21 % to 55 % on day 5, compared with those of SX41. Furthermore, these mutants demonstrated decreased cell counts and biofilm formation on biotite surfaces compared with SX41. Notably, the SX41∆traR mutant exhibited more pronounced effects on Al and Fe release from biotite, EPS production, and cell adsorption and biofilm formation on biotite surfaces compared with the SX41∆traI mutant. Moreover, the addition of biotite significantly upregulated the expression of traI and traR in SX41 and the complemented strains SX41∆traIR and SX41∆traRR. These findings underscore the pivotal role of the TraI/R system in the interactions between SX41 and biotite and highlight the distinct influences of traI and traR on Al and Fe release from biotite by SX41.