Presence and potential role of thermophilic bacteria in temperate terrestrial environments

Abstract

Organic-sulfur and nitrogen are major reservoirs of these elements in terrestrial systems although their cycling remains to be fully understood. Both sulfur and nitrogen mineralization are directly related to microbial metabolism. Mesophiles and thermophiles were isolated from temperate environments. Thermophilic isolates were classified within the Firmicutes, belonging to the Geobacillus, Brevibacillus and Ureibacillus genera, and showed optimum growth temperatures between 50ºC and 60ºC. Sulfate and ammonium produced was higher during growth of thermophiles both for isolated strains and natural bacterial assemblages. Sulfate and ammonium produced were positively related to organic nutrient load. Temperature also affected the release of sulfate and ammonium by thermophiles. Quantitative, real-time RT-PCR on environmental samples indicated that the examined thermophilic Firmicutes represented up to 3.4% of total bacterial community RNA. Temperature measurements during summer days showed values above 40ºC for over 10 h a day in soils from Southern Spain. These results support a potential role of thermophilic bacteria in temperate terrestrial environments by mineralizing organic sulfur and nitrogen ruled by the existence and length of warm periods.