Researchers at the University of Tartu have discovered a mechanism in bacteria that helps them adapt to fluoride, which is toxic to most organisms above relatively low threshold concentrations. Their discovery may represent a significant milestone in bioindustry, as it could help reduce the use of petrochemical products.
Fluoride is found as a mineral primarily in water, soil, and plants, but it is also an important raw material in several industries. For example, nearly a quarter of all pharma drugs contain fluorine, as it helps keeping the drugs active in the body longer and allow them to penetrate cell membranes more effectively. In addition, many hygiene, cosmetics, and electronic products contain fluorinated molecules. However, the synthesis of fluorine compounds is currently expensive and pollutes the environment.
To begin with, high temperatures are required to extract fluorine. This, in turn, requires special infrastructure, a great deal of energy, and a significant amount of petroleum-derived chemicals. The entire process releases fluorinated greenhouse gases into the environment. Their global warming potential (GWP) is up to 23,000 times greater than that of carbon dioxide (CO2).
Researchers view the soil-dwelling bacterium Pseudomonas putida as a promising alternative because it helps biodegrade pollutants and synthesize valuable chemicals, including fluorinated compounds. The bacterium is well-suited for this purpose because it can withstand a variety of physical and chemical stress conditions. In addition, P. putida grows rapidly, has a diverse metabolism, and scientists have effective tools at their disposal to modify its genes.
Microbes usually protect themselves from toxic levels of fluoride with special proteins. In the bacterium P. putida, the membrane protein CrcB pumps harmful fluoride ions out of the cells. Researchers from the Microbial Genetics Group at the Institute of Molecular and Cell Biology at the University of Tartu, led by Maia Kivisaar, investigated how P. putida adapts to a fluoride-containing environment, when it is deprived of the ability to produce the CrcB protein.
Genes with a New Function
The analysis showed that when the bacteria no longer had this primary defense system, spontaneous mutations occurred in some bacterial cells, making them more resistant to fluoride. The bacteria that survived in a fluoride-containing environment shared a specific characteristic: their regulatory gene PP_3125 had ceased to function.
It was found that PP_3125 inhibits the activity of the BenE-I gene. As far as it is currently known, the function of this gene is to transport benzoate out of cells, as benzoate is also toxic to cells at higher concentrations.
In bacterial strains engineered for the bioindustry, the biosynthesis of fluorine compounds must occur more efficiently. To achieve this, the bacteria must be able to tolerate higher intracellular concentrations of fluoride. As a result of their experiments, the researchers discovered a possible new mechanism for this: BenE-I helped the bacteria tolerate fluoride better, but did not reduce the amount of the toxic substance in the cells.
Researchers hope that identifying the exact molecular mechanism of BenE-I will help increase the biosynthesis of organofluoride compounds in new producer strains and make the use of bacteria in the bioindustry significantly more efficient.
The results of the study were published in the Journal of Bacteriology.
