Adaptation and Heavy Metal Degradation by Bacillus sp.: Insights Into Biofilm Formation, Exopolysaccharide (EPS) Production, and Antibiotic Resistance Under Copper (Cu) and Lead (Pb) Stress

An extensive concentration of heavy metals in our environment creates a harmful impact on living organisms, including microorganisms. Regardless of exploring the remediation potential of bacteria, their corresponding changes have not been extensively examined, which might be crucial before promoting bioremediation technology. The present study aimed to determine the effects of both essential (Cu) and nonessential (Pb) heavy metals on the bioactivity of a ubiquitous bacterium Bacillus sp., to gain knowledge about the adaptive mechanisms the strain has developed to withstand exposure to these metals. Bacterial adaptation is related to the formation of biofilm and the production of exopolysaccharides (EPSs) along with other tactics that assist in the survival of bacteria. When Bacillus sp. was cultured with Cu and Pb, changes in its bioactive characteristics were observed, such as a significant reduction in biofilm formation by 30.13% compared to the initial value. Moreover, the output of EPS by the bacterial strain in the presence of Pb increased to 0.782 mg/mL compared to the control condition, where no EPS was formed. In the presence of Cu, a low concentration of EPS (0.103 mg/mL) was detected. Moreover, the bacterial strain demonstrated adapted resistance to 6 out of 11 tested antibiotics, where the strain transformed from intermediate sensitivity to being susceptible to doxycycline, chloramphenicol, and gentamycin. Finally, the Cu- and Pb-degrading capacity of the bacterium was scrutinized using a flame atomic absorption spectrophotometer, where the bacterium exhibited significant degradation rates, breaking down 14.49% of Cu and 37.30% of Pb within 7 days. This research revealed the adaptability of the bacterial strain to survive in the presence of Cu and Pb while degrading them, by changing its bioactive properties, through the downregulation of biofilm formation, the productivity of EPS, and the heavy metal degradation process.