Bacteria can sneakily evade our best efforts at eradication by developing resistance to various pressures in their environment. For example, you may be familiar with antibiotic-resistant bacteria that stubbornly survive the usual deadly effects of antibiotics. However, the trade-off for developing a better defense is that it consumes a precious resource: energy. Bacteria must decide how to allocate limited energy resources to develop these resistances and spread them to neighbouring bacteria (through a process called conjugative transfer). There is a certain tipping point where it is worth the energy expenditure, but the details about these thresholds in aquatic environments are poorly understood.

A research team led by Assistant Professor Katayoun Amirfard of the Graduate School of Environmental Studies and Professor Daisuke Sano of the Graduate School of Engineering at Tohoku University analyzed how bacteria in aquatic environments distribute energy across diverse functions such as growth, biofilm formation (a protective barrier), conjugative transfer of antimicrobial resistance genes, and heavy‑metal tolerance. By clarifying bacterial energy investment strategies, this study is expected to contribute to improved water‑environment management.

"These findings offer vital clues to help us stop antibiotic resistant bacteria from spreading in water environment," says Sano.

The findings were published in Water Research on December 18, 2025.

The team employed a mathematical framework based on the Dynamic Energy Budget (DEB) theory. In particular, the researchers focused on how bacterial energy allocation changes over time when exposed to zinc oxide (ZnO), a widely used material commonly found in water environments. Using experimentally measured values, including substrate concentration, biofilm biomass, bacterial density, and conjugation efficiency, they estimated the parameters of the DEB‑based model.

This study reveals, for the first time, how bacteria in aquatic environments strategically allocate their limited energy among multiple physiological functions under environmental stress. This mechanistic understanding provides a new scientific foundation for assessing how pollutants influence the spread of antimicrobial resistance in the environment, which could inform more effective water‑quality management, pollution control, and public‑health strategies.

"Antimicrobial resistance is a growing global health concern, and its environmental dimensions are less understood than those in clinical settings," remarks Amirfard. "We hope this study helps to fill in that knowledge gap."