Thiosulfate-related microbial communities from four arid soils in the Southwestern United States

Sulfur-deficiency has been observed in arid and semi-arid soils. To explore sulfur cycling in arid soils, four (4) arid soils collected from the Southwestern United States were tested for 12 chemical constituents and moisture content, and soil microbial communities were assayed for the ability to utilize a set of 31 organic substrates using EcoPlates™. Soils were cultured for the presence of sulfur-utilizing bacteria using thiosulfate as the sulfur source. The densities of thiosulfate-utilizing bacterial populations were determined using viable plate counts and differential media. Results showed that the soils contained high amounts of sulfate, calcium and other minerals. Active soil microbial communities utilized 24–31 organic substrates. The density of thiosulfate-utilizing bacterial populations ranged from 105 colony forming units per gram (cfu g−1) to greater than 106 cfu g−1. Regression analyses showed that there were no statistically significant correlations between the density of thiosulfate-reducing bacteria and other tested variables. However, the high density of sulfur-related bacteria and high organic substrate utilization by the microorganisms suggests that these organisms may be important in sulfur and carbon cycling in these soils.

► Arid soils from the Southwestern USA were examined for sulfate and related bacteria.
► Soils contained 50–2000 ppm sulfate and >105 cfu g−1 thiosulfate-utilizing bacteria.
► Microbial communities used 24–31 organic substrates despite low humus in soil.
► Some soil bacterial communities used many types of organic C but not efficiently.
► Bacterial density not significantly correlated to soil moisture or other factors.