Quantification of viable endospores from a Greenland ice core

Authors


  • Editor: Rosa Margesin

Correspondence: Adrian Ponce California Institute of Technology, Pasadena, CA 91125, USA. Tel.: 818 354 8196; fax: 818 393 4773; e-mail: ponce@caltech.edu

Abstract

Endospores (i.e., bacterial spores) embedded in polar ices present an opportunity to investigate the most durable form of life in an ideal medium for maintaining long-term viability. However, little is known about the endospore distribution and viability in polar ices. We have determined germinable endospore concentrations of bacterial spores capable of germination in a Greenland ice core (GISP2 94 m, ID# G2-271) using two complementary endospore viability assays (EVA), recently developed in our laboratory. These assays are based on bulk spectroscopic analysis (i.e., spectroEVA), and direct microscopic enumeration (i.e., microEVA) of ice core concentrates. Both assays detect dipicolinic acid (DPA) release during l-alanine induced germination via terbium ion (Tb3+)-DPA luminescence. Using spectroEVA, the germinable and total bacterial spore concentrations were found to be 295±19 spores mL−1 and 369±36 spores mL−1, respectively, (i.e., 80% of the endospores were capable of germination). Using microEVA, the germinating endospore concentration was found to be 27±2 spores mL−1. The total cell concentration, as determined by DAPI stain fluorescence microscopy, was 7.0 × 103±6.7 × 102 cells mL−1. Culturing attempts yielded 2 CFU mL−1 (4°C). We conclude that endospores capable of germination in the GISP2 ice cores are readily determined using novel endospore viability assays.

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