Impact of lead (Pb²⁺) on the growth and biological activity of Serratia marcescens selected for wastewater treatment and identification of its zntR gene-a metal efflux regulator

Microorganisms isolated from contaminated areas play an important role in bioremediation processes. They promote heavy metal removal from the environment by adsorbing ions onto the cell wall surface, accumulating them inside the cells, or reducing, complexing, or precipitating these substances in the environment. Microorganism-based bioremediation processes can be highly efficient, low-cost and have low environmental impact. Thus, the present study aimed to select Pb²⁺-resistant bacteria and evaluate the growth rate, biological activity, and the presence of genes associated with metal resistance. Serratia marcescens CCMA 1010, that was previously isolated from coffee processing wastewater, was selected since was able to growth in Pb²⁺ concentrations of up to 4.0 mM. The growth rate and generation time did not differ from those of the control (without Pb²⁺), although biological activity decreased in the first hour of exposure to these ions and stabilized after this period. The presence of the zntR, zntA and pbrA genes was analysed, and only zntR was detected. The zntR gene encodes a protein responsible for regulating the production of ZntA, a transmembrane protein that facilitates Pb²⁺ extrusion out of the cell. S. marcescens CCMA 1010 demonstrated a potential for use as bioindicator that has potential to be used in bioremediation processes due to its resistance to high concentrations of Pb²⁺, ability to grow until 24 h of exposure, and possession of a gene that indicates the existence of mechanisms associated with resistance to lead (Pb²⁺).