Validation of a Clostridium Endospore Viability Assay and Analysis of Greenland Ices and Atacama Desert Soils▿ †

• Published in: Applied and Environmental Microbiology
• Main Authors: Yang, Wan-Wan, Ponce, Adrian
• Format: Text
• Language: English
• Published: American Society for Microbiology (ASM) 2011
• Subjects: Methods; Greenland; Greenland ice cores
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3067429; http://www.ncbi.nlm.nih.gov/pubmed/21296951; https://doi.org/10.1128/AEM.01966-10

A microscopy-based endospore viability assay (micro-EVA) capable of enumerating germinable Clostridium endospores (GCEs) in less than 30 min has been validated and employed to determine GCE concentrations in Greenland ices and Atacama Desert soils. Inoculation onto agarose doped with Tb3+ and d-alanine triggers Clostridium spore germination and the concomitant release of ∼108 molecules of dipicolinic acid (DPA) per endospore, which, under pulsed UV excitation, enables enumeration of resultant green Tb3+-DPA luminescent spots as GCEs with time-gated luminescence microscopy. The intensity time courses of the luminescent spots were characteristic of stage I Clostridium spore germination dynamics. Micro-EVA was validated against traditional CFU cultivation from 0 to 1,000 total endospores/ml (i.e., phase-bright bodies/ml), yielding 56.4% ± 1.5% GCEs and 43.0% ± 1.0% CFU. We also show that d-alanine serves as a Clostridium-specific germinant (three species tested) that inhibits Bacillus germination of spores (five species tested) in that endospore concentration regime. Finally, GCE concentrations in Greenland ice cores and Atacama Desert soils were determined with micro-EVA, yielding 1 to 2 GCEs/ml of Greenland ice (versus <1 CFU/ml after 6 months of incubation) and 66 to 157 GCEs/g of Atacama Desert soil (versus 40 CFU/g soil).