Bacterial Communities Associated with the Oxidation of Elemental Sulfur in Calcareous Soils of Oman

Purpose. Sulfur amendment plays an important role in the rehabilitation of saline and alkaline soils. Notably, the oxidation of elemental sulfur (S0) is primarily controlled by microbial activity. The influence of S0 amendments on its microbially-mediated oxidation in calcareous agricultural soils was investigated. Methods. Five different soils were incubated with increasing concentrations of S0 (0 to 1000 mg kg-1 in increments of 200) for eight weeks. Bacterial diversity was assessed by 16S V4 rRNA sequencing and compared with physicochemical and microbial parameters. Results. Amendment with S0 caused significant soil acidification with the maximum increase in sulfate and reduction in pH occurring in the fifth week of incubation. From the sixth week, the pH levels began to rise again as the soil buffering mechanisms overcame the production of SO42- resulting from the oxidation of S0. The 16S rRNA gene sequence analysis indicated that Proteobacteria, Firmicutes, and Actinobacteria were the most dominant phyla. The 16S rRNA diversity approach showed a considerable increase in the relative abundance of sulfur-oxidizing chemolithotrophs and autotrophic denitrifying sulfur-oxidizing bacteria after the addition of S0. Conclusion. The oxidation rate of S0 was significantly influenced by the interplay between soil physicochemical and biological properties. All five tested soils contained abundant sulfur-oxidizing bacterial communities with different S0 oxidation efficiencies; bioaugmentation practices are therefore not needed.