SdiA Improves the Acid Tolerance of E. coli by Regulating GadW and GadY Expression.

The acid tolerance mechanism is important forEscherichia colito resist acidic conditions encountered in mammalian host digestive tract environment. Here, we explored how the LuxR protein SdiA influencedE. coliacid tolerance ability in the context of the glutamate- and glutamine-dependent acid resistance system (AR2). First, using a growth and acid shock assay under different acid stresses, we demonstrated that the deletion ofsdiAinSM10 lambda pirorBW25113led to impaired growth under the acidic environment of pH 3-6, which was restored by complementary expression of SdiA. Next, transcriptome sequencing and qPCR disclosed that the expression of glutamate decarboxylase W (GadW) and GadY, the key members of the AR2 system, were regulated by SdiA. Further, beta-galactosidase reporter assays showed that the promoter activity ofgadWandgadYwas positively regulated by SdiA. Moreover, qPCR and beta-galactosidase reporter assays confirmed that the regulation of SdiA on GadW, but not GadY, could be enhanced by quorum sensing (QS) signal molecules AHLs. Collectively, these data suggest that SdiA plays a crucial role in acid tolerance regulation ofE. coli. Our findings provide new insights into the important contribution of quorum sensing system AHLs-SdiA to the networks that regulate acid tolerance.