Slow leakage of Ca-dipicolinic acid from individual Bacillus spores during initiation of spore germination

Shiwei Wang, Peter Setlow and Yong-qing Li

When exposed to nutrient or non-nutrient germinants, individual Bacillus spores can return to life through germination followed by outgrowth. Laser tweezers Raman spectroscopy, and either differential interference contrast or phase contrast microscopy were used to analyze the slow dipicolinic acid (DPA) leakage (normally ∼20% of spore DPA) from individual spores that takes place prior to the lag time, Tlag, when spores begin rapid release of remaining DPA. Major conclusions from this work with Bacillus subtilis spores were: 1) slow DPA leakage from wild-type spores germinating with nutrients did not begin immediately after nutrient exposure, but only at a later heterogeneous time T1; 2) the period of slow DPA leakage (ΔTleakage = Tlag - T1) was heterogeneous among individual spores, although the amount of DPA released in this period was relatively constant; 3) increases in germination temperature significantly decreased T1 times, but increased values of ΔTleakage; 4) upon germination with L-valine for 10 min followed by addition of D-alanine to block further germination, all germinated spores had T1 times less than 10 min, suggesting that T1 is the time when spores become committed to germinate; 5) elevated levels of SpoVA proteins involved in DPA movement in spore germination decreased T1 and Tlag times, but not the amount of DPA released in ΔTleakage; 6) lack of the cortex-lytic enzyme CwlJ increased DPA leakage during germination due to longer ΔTleakage times in which more DPA was released; and 6) there was slow DPA leakage early in germination of B. subtilis spores by the non-nutrients CaDPA and dodecylamine and in nutrient germination of Bacillus cereus and Bacillus megaterium spores. Overall, these findings have identified and characterized a new early event in Bacillus spore germination.

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