Energy allocation trade-offs among conjugative transfer, biofilm formation, and heavy metal resistance: a dynamic energy budget theory perspective

Plasmid-mediated bacterial conjugation is a significant driver of antimicrobial resistance (AMR) dissemination in the environment, particularly within surface-attached biofilms, where spatial proximity facilitates gene exchange. Environmental stressors, such as heavy metals, can influence both the structural development of biofilms and the frequency of conjugation, imposing metabolic burdens that force bacteria to reprioritize their energy use. In this study, we used a simplified Dynamic Energy Budget (DEB)-based modeling framework to evaluate energy allocation in a single-strain bacterial population exposed to varying concentrations of zinc oxide (ZnO; 0-0.1 g/L). The model incorporates substrate assimilation, reserve dynamics, and energy partitioning toward growth, maintenance, metal resistance, biofilm formation, and conjugation. Experimental data were collected every 12 h for 48 h, including total organic carbon (TOC, mg/L), biomass (CFU/mL), intracellular adenosine triphosphate (ATP, mol/mL), conjugation frequency (transconjugants/donor), and biofilm density (OD₅₅₀). Ordinary Differential Equation (ODE)-based simulations over 60 h showed that at 0.1 g/L ZnO, reserve energy and substrate declined approximately 3.1- and 1.9-fold, respectively (vs around 5- and 2.9-fold in control), indicating reduced depletion. Discrete-time-point flux models revealed conjugation demanded 17% of total energy at 36 h under 0.01 g/L ZnO, and 10% under 0.1 g/L at 60 h, while energy allocated to biofilm formation remained ≤ 3% under the highest ZnO concentration. Overall, the model reveals key trade-offs in bacterial energy allocation and provides mechanistic insight into how metal stress may shape biofilm formation and conjugation dynamics. Its modular and data-driven structure offers a basis for understanding microbial adaptation and AMR propagation in metal-contaminated environments.