Heavy metals bioremediation: Cd2+, Pb2+ and Zn2+ bioremoval by Serratia marcescens CCMA1010 in aqueous solution

Microorganisms offer cost-effective and sustainable solutions for the bioremediation of toxic metals. S. marcescens CCMA1010 was investigated for its growth and metal removal potential in aqueous solution with Cd²⁺, Pb²⁺, and Zn²⁺. The bacterium tolerated all three metals, with a minimum inhibitory concentration (MIC) ranking of Zn²⁺ > Pb²⁺ > Cd²⁺. Remarkably, Pb²⁺ had minimal impact on growth compared to the control. A brown coloration in Pb²⁺ treatments suggested the bioprecipitation. FTIR analysis confirmed spectral changes linked to sulphate and phosphate groups, supporting the probability of this mechanism. No similar evidence was found for Cd²⁺ or Zn²⁺. The bioremoval experiment was designed to construct a predictive model and identify the optimal conditions for maximum metal uptake ( q ), using a Rotatable Central Composite Design (RCCD) with 27 experimental runs, including factorial points, axial points, and three central points. The statistical modeling (P-value) showed that quadratic models for Cd²⁺ and Pb²⁺ uptake were significant (p < 0.05), with initial metal concentration as the main influencing factor. The p-value for Zn²⁺ ( q ) was not significant (p > 0.05). The F-values indicate that both models (Cd²⁺ and Pb²⁺) were statistically significant, with only a 0.01% and 0.46% probability, respectively, that such high F-values could have occurred due to random noise. Variables such as pH and interactions between multiple metals were not statistically significant under the tested conditions. These results highlight S. marcescens CCMA1010 as a promising candidate for heavy metal bioremediation, particularly for lead removal through bioprecipitation pathways.