Molecular Insight into The Oxidative Stress Response Mechanisms of Marine Bacteria Against the Priority Heavy Metals

Abstract

Marine bacteria thriving in the mangrove ecosystem are major drivers of elemental cycles. Anthropogenic activities such as industrial effluents, agricultural runoffs, etc., elevate the heavy metals concentration of the mangrove ecosystem. The heavy metals concentration in the environment above the permissible limit, particularly lead (>0.05 mg/l) and cadmium (>0.005 mg/l), have system-level effects on the structural and functional attributes of bacteria thriving in the ecosystem. Present study reports the genotoxic effect of heavy metals on marine bacteria and their adaptation strategies. Comparative analysis between two bacterial strains, Bacillus stercoris GST-03 and Pseudomonas balearica DST-02 isolated from the Bhitarkanika mangrove ecosystem, Odisha, India, showed cellular injuries in response to heavy metal stressors as evident by declined growth, elevated levels of reactive oxygen species (ROS) disrupting the equilibrium in between the formation of free radicals and antioxidant synthesis, leading to production of DNA damage product (8-hydroxydeoxyguanosine). The bacterium P. balearica DST-02 showed higher tolerance towards heavy metals (Lead and Cadmium) compared to B. stercoris GST-03. The adaptation strategies of the strains revealed a significant role of GST in ROS scavenging activity and the involvement of Nucleotide excision repair (NER) and SOS response pathways. However, irreparable DNA damage was observed at 1000 ppm of Pb in P. balearica DST-02 and at 200 ppm Cd in both B. stercoris GST-03 and P. balearica DST-02. The current findings depict the impact of priority heavy metals on the mangrove bacteria at the genetic level in terms of their survival, DNA damage, and repair efficiency providing insight into the instantaneous response of haploid organisms, their adaptability towards heavy metals, and overall consequences on the ecosystem functioning