Fluoride is usually discussed in the context of toothpaste, drinking water, or industrial pollution. At the cellular level, however, it is a potent toxin. The ion can interfere with essential metabolic reactions, disrupt enzyme activity, and damage the finely balanced chemistry that allows microbes to grow. Now, researchers at the University of Tartu have uncovered an unexpected bacterial strategy for surviving fluoride exposure—one that could eventually help turn microorganisms into more efficient factories for producing fluorinated chemicals.
The study focused on Pseudomonas putida, a soil-dwelling bacterium already known for its ability to break down pollutants and manufacture commercially valuable compounds. Unlike many industrial microbes, P. putida can tolerate substantial physical and chemical stress, grows rapidly, possesses a highly flexible metabolism, and can be genetically engineered using well-established laboratory tools. These characteristics have made it an attractive candidate for biotechnology, particularly for replacing some petroleum-based chemical processes with biological production.
Fluorinated molecules are essential in a wide range of modern products. Nearly one-quarter of pharmaceutical drugs contain fluorine because the element can improve a compound’s stability, prolong its activity in the body, and influence how effectively it crosses cell membranes. Fluorinated chemicals are also used in hygiene products, cosmetics, electronics, and advanced materials. Yet conventional fluorine chemistry is costly and environmentally demanding. Industrial production often requires high temperatures, specialized infrastructure, large amounts of energy, and petroleum-derived reagents. It can also release fluorinated greenhouse gases whose global warming potential is thousands of times greater than that of carbon dioxide.
Bacteria have evolved several ways to defend themselves against fluoride. In P. putida, one important line of protection is provided by CrcB, a membrane protein that exports fluoride ions from the cell. By lowering the internal concentration of fluoride, CrcB helps prevent the ion from interfering with vulnerable biochemical processes. The University of Tartu team, led by Maia Kivisaar at the Institute of Molecular and Cell Biology’s Microbial Genetics Group, asked what would happen if this primary defense system were removed.
The researchers examined bacterial populations that could no longer produce CrcB and exposed them to a fluoride-containing environment. Most cells were expected to become highly vulnerable, but some survived. Genetic analysis revealed that these survivors had independently acquired mutations in the same regulatory gene, PP_3125. The repeated appearance of mutations in this gene suggested that the bacteria were not simply escaping damage by chance. Instead, the loss of PP_3125 appeared to activate a previously unrecognized route to fluoride resistance.
Further experiments showed that PP_3125 normally suppresses the activity of BenE-I. The gene was previously associated with the transport of benzoate, an organic compound that can also become toxic to bacterial cells at elevated concentrations. When PP_3125 stopped functioning, BenE-I became more active. This result connected a regulatory pathway apparently linked to benzoate resistance with the bacterium’s ability to survive fluoride stress, revealing a surprising example of how bacterial systems can acquire or expose new biological functions.
The most striking finding was that BenE-I did not appear to protect the cells by simply pumping fluoride out. Instead, bacteria carrying the altered regulatory system tolerated higher intracellular fluoride concentrations. This distinction is important. A conventional resistance mechanism reduces the amount of a toxic compound inside the cell, while the BenE-I-associated response seems to make the cell more resilient to the damage caused by the compound. The precise molecular explanation remains unknown, but the transporter may influence membrane physiology, ion balance, cellular signaling, or the activity of other stress-response systems.
That distinction could be especially valuable for synthetic biology. Bacterial strains designed to manufacture organofluorine compounds must not only produce the desired molecules; they must also endure the chemical conditions created during production. If fluoride accumulates inside engineered cells, it can slow growth or shut down biosynthetic pathways. A mechanism that increases tolerance without removing fluoride could therefore allow cells to continue operating in environments where conventional defenses are insufficient. In principle, this could improve yields and reduce the need for harsh chemical processing.
The researchers now hope to determine exactly how BenE-I produces this protective effect and how PP_3125 controls it at the molecular level. Understanding the transporter’s structure, cellular location, and interactions with other proteins may allow scientists to optimize P. putida for the biological production of fluorinated compounds. The work does not yet provide an industrial replacement for conventional fluorine synthesis, but it identifies a potentially powerful genetic switch for engineering more robust microbial factories. Published in the Journal of Bacteriology, the study demonstrates how adaptive evolution can reveal hidden functions in bacterial genes—and how a microbe’s struggle to survive a toxin can point toward cleaner chemical manufacturing.
Subject of Research: Cells
Article Title: Adaptive evolution of Pseudomonas putida in the presence of fluoride exposes novel functions of a benzoate transporter
Web References: https://doi.org/10.1128/jb.00479-25
References: Journal of Bacteriology, DOI: 10.1128/jb.00479-25
Keywords: Fluoride resistance, Pseudomonas putida, BenE-I, PP_3125, CrcB, bacterial adaptation, synthetic biology, organofluorine compounds, microbial biotechnology, green chemistry
