PMC

Percentage of spores in the total population that can be determined by EVA, phase-contrast microscopy, and CFU enumeration. Error bars represent 1 standard deviation.

Excitation spectrum of ice core concentrate with 1 μM Tb³⁺, monitoring emission intensity at 543 nm (solid line). The dotted line shows the excitation spectrum for 1 μM DPA with 10 μM Tb³⁺. The dashed line shows the negative control for an ice core with 1 μM Tb³⁺.

Percentage of spore inactivation as a function of UV dosage. •, CFU inactivated by exposure; ▴, inactivation measured by EVA; ▪, inactivation measured by phase-contrast microscopy. Error bars represent 1 standard deviation but are hidden because they are smaller than the data point symbols.

(A) Correlation between phase-contrast enumeration and Tb³⁺-DPA luminescence assay for quantification of total spore concentration over 2 orders of magnitude. (B) Correlation between phase-contrast enumeration and Tb³⁺-DPA luminescence assay for quantification of germinable spores over 2 orders of magnitude. The lines shown indicate a 1:1 correspondence. Error bars represent 1 standard deviation.

(A) Germination time course of B. atrophaeus spores, which shows Tb-DPA luminescence intensity as a function of time. l-Alanine addition at time zero triggers the germination process, during which DPA is released. The luminescence intensity after autoclaving was normalized. (B to D) Phase-contrast images of spores, which appear as phase-bright bodies when intact, after autoclaving (B), after germination is complete (C), and prior to l-alanine addition (D). The image contrast has been enhanced for clarity.

(A) Absorption-energy transfer-emission mechanism for the Tb³⁺-DPA luminescence assay. (B) Cuvettes containing solutions of 1 mM Tb³⁺, 1 mM Tb³⁺ plus 1 μM DPA, and 1 mM DPA under UV (254 nm) light. (C) Tb-DPA luminescence intensity calibration curve. Error bars represent 1 standard deviation.