Genome-wide transcriptomic insights into temperature-driven suppression of violacein biosynthesis in Massilia atriviolacea SODT

Massilia atriviolacea SODᵀ, a novel bacterial species isolated from Hefei soil, produces violacein as its predominant purple pigment, confirmed by high-performance liquid chromatography, nuclear magnetic resonance, and mass spectrometry analyses. Notably, high temperature (33 °C) significantly inhibited violacein production, while cultivation at 28 °C fully restored pigment synthesis—a reversible regulatory pattern distinct from other violacein-producing strains. Transcriptomic analysis revealed 1997 differentially expressed genes (DEGs) at 33 °C, with strong downregulation of the vioABCDE operon. Genes involved in tryptophan biosynthesis (e.g., trpE, trpG) were only slightly repressed, and tryptophan supplementation experiments confirmed that this did not limit violacein production. qRT-PCR validated the strong downregulation of the vioABCDE operon at high temperatures, consistent with RNA-seq data. The genome of M. atriviolacea SODᵀ comprises a 7.43-Mb circular chromosome (65.29 mol% G+C) encoding 6596 CDSs, including those for carbon metabolism and amino acid transport. KEGG-based metabolic pathway analysis revealed that strain SODᵀ harbors all functional gene clusters required for violacein biosynthesis, forming a complete biosynthetic pathway. The purified violacein exhibited potent anticancer activity against HeLa cells (IC₅₀ = 1.92 µg/mL), primarily via inducing mitochondrial membrane potential dysfunction. This study demonstrates that high temperature suppresses violacein biosynthesis by transcriptionally repressing the vioABCDE operon, not by limiting tryptophan supply. These findings provide insights for optimizing industrial violacein production and advancing its utility as a natural food colorant and biomedical agent.