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

Abstract

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 ¹⁹ F-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.