Regulation of high-density cell growth by Rgg transcription factors in Streptococcus thermophilus S-3

Streptococcus thermophilus S-3 is an industrial dairy fermentation species, which can modulate growth and metabolism through quorum sensing (QS). However, the regulatory mechanisms governing high-density bacterial proliferation remain elusive in S. thermophilus S-3. This study focuses on Rgg, a quorum sensing-associated transcription factor, examining its regulatory role in high-density growth dynamics.

Three Rgg putative transcriptional regulators (orf383, orf447, and orf1010) in S. thermophilus S-3 were identified, and their evolutionary conservation and conserved DNA-binding domains were characterized, supporting their predicted role in transcriptional regulation of high-density growth. Phenotypic analysis showed that the S-3Δ447 mutant exhibited 30.9% lower maximum optical density and 68.8% lower viability than wild-type strains. Transcriptomic profiling revealed Rgg-dependent dysregulation: 209 upregulated/272 downregulated genes at 7 h, 82 downregulated/20 upregulated at 12 h, and 25 upregulated/33 downregulated at 20 h. KEGG pathway analysis highlighted enrichment in ABC transporters and amino/nucleotide sugar metabolic. Notably, oppC/oppD downregulation disrupted SHP-Rgg binding, impairing oligopeptide signaling. Furthermore, ganP/ganQ suppression reduced lactose uptake capacity and ultimately suppressed cellular proliferation. Conversely, artP upregulation promoted arginine catabolism preference, effectively compensating for observed growth deficiencies.

This study elucidated the regulatory role of rgg genes in the high-cell-density growth of S. thermophilus S-3. Rgg coordinates high-density cell proliferation through the dual regulation of peptide-mediated QS initiation and carbon-nitrogen metabolic flux reprogramming. © 2026 Society of Chemical Industry.