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Fluoride movement into and out of Bacillus spores and growing cells and effects of fluoride accumulation on spore properties

Dong, W., Setlow, P.
Journal of applied microbiology 2019 v.126 no.2 pp. 503-515
Bacillus cereus, Bacillus subtilis, cell growth, heat tolerance, pH, sodium fluoride, spore germination, spores
AIMS: To investigate effects of fluoride ion (F⁻) on, and kinetics of its movement into and out of, spores and growing cells of Bacillus species. METHODS AND RESULTS: Effects of F⁻ on Bacillus cell growth, spore germination and outgrowth and heat resistance were investigated, as well as F⁻ movement into and out of spores using ¹⁹F‐NMR. F⁻ inhibited Bacillus subtilis spore germination and outgrowth, and YhdU, now named FluC, was crucial to prevent F⁻ accumulation in growing cells and to minimize F⁻ inhibition of spore germination. Dormant wild‐type, yhdU and coat defective B. subtilis spores, and Bacillus cereus spores incubated in 40 mmol l⁻¹ NaF for 48 h accumulated 2–2·6 mol l⁻¹ F⁻ and its movement into Bacillus spores was highest at low pH. Bacillus subtilis spores lacking Ca‐dipicolinic acid accumulated higher F⁻ levels than wild‐type spores. CONCLUSIONS: These results are consistent with F⁻ incorporation into the dormant spore core, and as HF and/or NaF, but not CaF₂. YhdU played no significant role in F⁻ uptake or efflux in dormant spores, but assisted in F⁻ export early in spore germination. SIGNIFICANCE AND IMPACT OF STUDY: This knowledge provides new insight into effects of F⁻ on Bacillus cells and spores and how this anion moves into, and out of spores.