Applications of a Rapid Endospore Viability Assay for Monitoring UV Inactivation and Characterizing Arctic Ice Cores†

• Published in: Applied and Environmental Microbiology
• Main Authors: Shafaat, Hannah S., Ponce, Adrian
• Format: Text
• Language: English
• Published: American Society for Microbiology 2006
• Subjects: Methods; Arctic; Greenland; Greenland Ice Sheet Project; ice core; Ice Sheet
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1610317; http://www.ncbi.nlm.nih.gov/pubmed/17021233; https://doi.org/10.1128/AEM.00255-06

We have developed a rapid endospore viability assay (EVA) in which endospore germination serves as an indicator for viability and applied it to (i) monitor UV inactivation of endospores as a function of dose and (ii) determine the proportion of viable endospores in arctic ice cores (Greenland Ice Sheet Project 2 [GISP2] cores; 94 m). EVA is based on the detection of dipicolinic acid (DPA), which is released from endospores during germination. DPA concentrations were determined using the terbium ion (Tb3+)-DPA luminescence assay, and germination was induced by l-alanine addition. The concentrations of germinable endospores were determined by comparison to a standard curve. Parallel EVA and phase-contrast microscopy experiments to determine the percentage of germinable spores yielded comparable results (54.3% ± 3.8% and 48.9% ± 4.5%, respectively), while only 27.8% ± 7.6% of spores produced CFU. EVA was applied to monitor the inactivation of spore suspensions as a function of UV dose, yielding reproducible correlations between EVA and CFU inactivation data. The 90% inactivation doses were 2,773 J/m2, 3,947 J/m2, and 1,322 J/m2 for EVA, phase-contrast microscopy, and CFU reduction, respectively. Finally, EVA was applied to quantify germinable and total endospore concentrations in two GISP2 ice cores. The first ice core contained 295 ± 19 germinable spores/ml and 369 ± 36 total spores/ml (i.e., the percentage of germinable endospores was 79.9% ± 9.3%), and the second core contained 131 ± 4 germinable spores/ml and 162 ± 17 total spores/ml (i.e., the percentage of germinable endospores was 80.9% ± 8.8%), whereas only 2 CFU/ml were detected by culturing.