Marine Microbe Shows Exceptional Ability to Remove Toxic Metals
Heavy metal contamination in oceans and estuaries poses a serious threat to ecosystems and human health. A newly published study introduces Streptomyces sp. K13, a marine actinobacterium isolated from the northeast coast of Tamil Nadu, India, as a highly effective and eco-friendly solution for mercury and cadmium pollution.
Discovery and Identification of Strain K13
Out of 18 actinobacterial strains collected from marine sediment samples, Streptomyces sp. K13 demonstrated the strongest tolerance to both HgCl₂ and CdCl₂ up to concentrations of 150 mg/L. Molecular identification through 16S rRNA sequencing confirmed its affiliation with the Streptomyces genus.
High Bioremediation Efficiency Under Optimized Conditions
Using Response Surface Methodology (RSM), researchers optimized nutrient conditions for maximizing metal removal. Under these optimized conditions:
- Mercury removal reached 73.1% within 15 days using the dithizone assay.
- Cadmium tolerance and removal were confirmed through MIC and turbidometric analysis.
Biofilm Formation and EPS Production Boost Detoxification
Strain K13 produced substantial biofilms and exopolysaccharides (EPS) under metal stress. EPS yields increased proportionally with metal concentration, reaching:
- 34.58 mg/L under mercury stress
- 28.37 mg/L under cadmium stress
These secreted polymers are crucial for binding, immobilizing, and reducing the toxicity of metal ions.
Adsorption Studies Confirm Strong Binding, Especially for Mercury
Isotherm modelling (Langmuir, Freundlich, Temkin) revealed:
- Higher adsorption capacity for mercury (150.73 mg/g)
- Stronger binding affinity to functional groups such as O–H, carbonyl, and sulfoxide, as confirmed by FT-IR
- SEM analysis showed significant surface changes after metal exposure
Bioreactor Trials Achieve Up to 76% Heavy Metal Removal
In a 20-day lab-scale bioreactor experiment:
- 76% of mercury and
- 73% of cadmium
were successfully removed from contaminated water.
The microbe also adapted well to prolonged metal stress, maintaining stable growth after initial inhibition.
Toxicity Tests Show Successful Detoxification
The Allium cepa root tip assay showed heavy metals caused severe chromosomal damage in untreated samples. However, metals treated with K13 showed no chromosomal abnormalities, confirming effective detoxification.
Conclusion: A Promising Candidate for Scalable Marine Bioremediation
This is the first report of a marine actinobacterial strain from Tamil Nadu demonstrating dual removal of mercury and cadmium using biosorption and bioreactor-based processes. The results highlight K13’s potential for:
- Eco-friendly remediation
- Future pilot-scale deployment
- Field-level treatment of metal-contaminated waters
Reference
Elumalai, L., Nagarajan, S., Abass, K.S. et al. Bioremediation of mercury and cadmium using marine Streptomyces sp. K13: biosorption, bioreactor and its toxicity studies. Environ Geochem Health 47, 518 (2025). https://doi.org/10.1007/s10653-025-02820-2
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