Copper Tolerance and Transcriptomic Response After Prolonged Cu2+ Exposure in the Antarctic Psychrophile Rhodoglobus galactosidasius Strain CPHL_1T

Abstract The Antarctic psychrophilic actinomycete Rhodoglobus galactosidasius strain CPHL_1 T was investigated to characterize its physiological and transcriptional responses after prolonged copper exposure. Although copper is an essential trace element for microbial metabolism, it becomes toxic when cellular homeostasis is disrupted. While copper resistance mechanisms have been extensively studied in model bacteria, the responses of poorly characterized microorganisms to sustained copper stress remain comparatively underexplored. Growth experiments revealed concentration-dependent effects of Cu 2+ . Low copper concentrations produced an apparent stimulatory effect consistent with a hormetic-like response, while higher concentrations delayed or inhibited growth. Transcriptomic analysis identified 974 differentially expressed genes between control and copper-exposed cultures, and principal component analysis showed a clear separation between the two conditions. Differential expression and functional enrichment analyses revealed extensive transcriptional reorganization involving metal-responsive regulation, multicopper oxidases, iron-sulfur cluster maintenance, protein quality control, and DNA repair, together with differential modulation of metabolic, transcriptional, and genome maintenance functions. Preliminary ICP-MS analyses further demonstrated measurable biomass-associated copper retention, although the mechanisms underlying copper association could not be resolved. These findings provide an initial transcriptome-wide characterization of the response of R. galactosidasius to prolonged copper exposure. Although several of the responsive pathways involved conserved bacterial stress mechanisms, their coordinated modulation in this bacterium expands current knowledge of the integration of metal homeostasis, cellular maintenance, and stress responses under prolonged copper exposure.