Functional insights into the chloroplast rps2 gene from Dunaliella salina: Enhanced cadmium adsorption and resistance in recombinant bacteria

Cadmium (Cd) is a toxic heavy metal that poses significant ecological and health risks. Marine microalgae, such as Dunaliella salina, exhibit remarkable Cd adsorption and tolerance, making them valuable models for studying Cd toxicity and bioremediation. This study identified the chloroplast 30S ribosomal protein gene (rps2) as the most Cd-sensitive gene in D. salina. At 10 μg/L Cd, chloroplast genome-encoded genes related to translation and photosynthesis were upregulated, with rps2 displaying sustained upregulation, whereas at 100 μg/L Cd, these genes were downregulated, with rps2 exhibiting continuous downregulation. rps2 transcription increased at low Cd levels (2.5 and 25 μg/L) but declined at higher concentrations (250 and 2500 μg/L), while protein levels remained stable at low Cd levels (2.5, 25 and 250 μg/L) but dropped significantly at high levels (2500 μg/L). The recombinant strain exhibited enhanced Cd tolerance and adsorption, with higher intracellular Cd levels and reduced Cd in the supernatant compared to controls. The RPS2 protein was detected in both cells and supernatants. Molecular weight discrepancies (63 kDa in D. salina vs. 99 kDa in recombinant strains) suggest post-translational cleavage in D. salina. These findings underscore the critical role of rps2 in Cd biosorption and tolerance, offering a promising approach for aquatic Cd bioremediation. Furthermore, this study provides a theoretical foundation for further exploring of the molecular mechanisms of the rps2 gene in response to heavy metal stress, and highlights potential non-ribosomal functions and post-translational modifications of ribosomal proteins.