Importance of environmental factors on the growth of Thermoactinomyces thalpophilus

Abstract

The germination and growth of endospores from Thermoactinomyces thalpophilus in two soils, a sand silt loam and a silt clay loam was investigated under a range of environmental conditions. A 50-fold increase in the recovery of T. thalpophilus was observed after 28 d growth in silt clay loam soil, when compared to the original inoculum (8.85×10 4 cfu g −1 dry soil), with similar results obtained for this soil over a range of soil moisture contents (5–50% w/w) and at temperatures of 30 and 45°C. In contrast, no increase in the recovery of T. thalpophilus was detected when endospores (2.53×10 5 cfu g −1 dry soil) were inoculated into sand silt loam soil. However, when sterile farmyard manure (2% w/w) was added to sand silt loam soil, a 50-fold increase in the numbers of T. thalpophilus isolated was observed over 28 d incubation. Analysis of the sand silt loam soil showed that organic C and N content, pH, and the C-to-N ratio of the soil had all increased significantly upon addition of farmyard manure, resulting in the growth of T. thalpophilus endospores in a soil which previously could not sustain growth. Addition of manure to the silt clay loam led to a 70% increase in recovery of T. thalpophilus. Growth and respiratory measurements of T. thalpophilus released into sterile manure confirmed the ability of these endospores to show rapid germination, with respiratory activity detected after 7 h, reaching a maximum value (700 μmol CO 2 h −1 g −1 dry manure) 11 h after inoculation, resulting in a 600-fold increase (final recovery, 2.38×10 9 cfu g −1 dry manure) in the recovery of T. thalpophilus. We conclude that T. thalpophilus is capable of growth in soils at temperatures as low as 30°C and under a range of soil moisture conditions. Further, enhanced growth in soils with additions of manure could be observed. These results support the idea that Thermoactinomyces endospores isolated from ancient soils containing agricultural debris may have remained dormant in soil following a brief period of rapid growth immediately following deposition.