Characterization and Transcriptomic Analysis of Antarctic <i>Planococcus</i> sp. Mutant with Enhanced Carotenoid Content

Carotenoids are industrially important antioxidants, and microbial production represents a sustainable and scalable alternative to plant extraction and chemical synthesis. The recently reported complete genome sequence of the Antarctic bacterium <i>Planococcus</i> sp. PAMC21323 indicates its promise as a robust microbial chassis for carotenoid biosynthesis. In this study, we systematically investigated the genetic architecture underlying carotenoid biosynthesis in PAMC21323. Random mutagenesis using ethyl methanesulfonate generated pigment-variant strains, from which a carotenoid-overproducing mutant, R07, was selected through colony pigmentation screening and HPLC analysis. Integrated genome mining, homology-based annotation, and comparative RNA-seq analysis of the wild type and R07 were employed to reconstruct the carotenoid biosynthetic pathway and to characterize global transcriptional changes linked to overproduction. Genome-scale annotation newly defined a CrtM-CrtN-CrtP-CrtNc gene cluster, demonstrating that PAMC21323 synthesizes C₃₀ rather than C₄₀ carotenoids. Comparative transcriptomic profiling further revealed upregulation of upstream MEP pathway genes and concomitant downregulation of competing non-carotenoid terpenoid branches in R07, indicating effective redirection of metabolic flux toward carotenoid biosynthesis. Collectively, these findings establish the molecular framework for C₃₀ carotenoid production in PAMC21323 and highlight a carotenoid-enriched mutant strain as a valuable platform for future metabolic engineering and biotechnological applications in extreme environments.