THIOBACILLUS POPULATIONS IN SOME AGRICULTURAL SOILS

A survey was made of the occurrence of autotrophic thiobacilli in 43 Scottish agricultural soils. Acidophilic thiobacilli, typically Thiobacillus thiooxidans, were not detected but neutrophilic thiobacilli, typically T. thioparus, were found in 84% of the soils with MPN counts ranging from l to 105 g-1 soil. There was a significant but poor negative correlation between log numbers of thiobacilli and sample latitude but with no other soil feature measured. Where determined, higher counts of S-oxidizing heterotrophs (> 105 g-1 soil) were found in all soils. Addition of elemental sulphur to two soils caused a rapid increase in the numbers of neutrophilic thiobacilli and, in one soil, the appearance of acidophilic thiobacilli. © 1990.