Multi-locus real-time PCR for quantitation of bacteria in the environment reveals Exiguobacterium to be prevalent in permafrost


  • Editor: Rosa Margesin

Correspondence: Debora Frigi Rodrigues, Michigan State University, NASA Astrobiology Institute and Center for Microbial Ecology, 540 Plant & Soil Science Bldg., East Lansing, MI 48824-1325, USA. Tel.: +517 355 0271 ext. 1284; fax: +517 353 2917; e-mail:


We developed a multi-locus quantitative PCR approach to minimize problems of precision, sensitivity and primer specificity for quantifying a targeted microbial group in nature. This approach also avoids a systematic error in population quantitation when 16S rRNA genes are used because of copy number heterogeneity. Specific primers were designed to assess the abundance of psychrotrophic and mesophilic Exiguobacterium spp. that excluded the thermophilic members of the genus. The chosen primers targeted genes for DNA gyrase B (gyrB), the beta subunit of the RNA polymerase gene (rpoB) and a hypothetical gene so far found only in this group. The results demonstrate that the multiple primer approach provides a more reliable estimate of population density; that the targeted Exiguobacterium group is found at a median density of 50 000 gene copies per μg of total community DNA in 27 of 29 permafrost soils but was found in only one of the four temperate and tropical soils tested.