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Applied and Environmental Microbiology, October 2006, p. 6808-6814, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.00255-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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

Hannah S. Shafaat and Adrian Ponce*

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

Received 1 February 2006/ Accepted 22 June 2006

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.

* Corresponding author. Mailing address: Jet Propulsion Laboratory, MS 302-205, 4800 Oak Grove Drive, Pasadena, CA 91109. Phone: (818) 354-8196. Fax: (818) 393-4773. E-mail: Adrian.Ponce{at}jpl.nasa.gov.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, October 2006, p. 6808-6814, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.00255-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Yung, P. T., Ponce, A. (2008). Fast Sterility Assessment by Germinable-Endospore Biodosimetry. Appl. Environ. Microbiol. 74: 7669-7674 [Abstract] [Full Text]  
  • Rohde, R. A., Price, P. B., Bay, R. C., Bramall, N. E. (2008). In situ microbial metabolism as a cause of gas anomalies in ice. Proc. Natl. Acad. Sci. USA 105: 8667-8672 [Abstract] [Full Text]  


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