New insights into the antagonistic effect of AMF and SOB: A preliminary study on the ability of Funneliformis mosseae to inhibit sulfur oxidation by Acidithiobacillus thiooxidans

Soybean (Glycine max) is a sulfur-loving crop. Continuous cropping leads to sulfur deficiency and soil acidification. In this study, we used soybean as a host plant to investigate the interaction between Funneliformis mosseae (F. mosseae) and Acidithiobacillus thiooxidans (A. thiooxidans), as well as their impact on sulfur transformation. The experiment employed pot cultivation, a dual-chamber system, and shake-flask culture methods, using F. mosseae and A. thiooxidans as experimental inoculants. It measured the transformation and cycling of sulfur compounds in the soil, the expression of functional genes related to sulfur cycling, and the phenotypic and physiological indicators of soybeans and A. thiooxidans. The results show that single inoculation with F. mosseae effectively increased soil available sulfur content. In contrast, single or combined inoculation with A. thiooxidans caused a decline in soil available sulfur content, inhibited soybean growth, and reduced the abundance of sulfur cycling genes (dsrA, soxY, yedZ, and apsA). This indicates a clear antagonistic effect between F. mosseae and A. thiooxidans. These results indicate that F. mosseae, in collaboration with A. thiooxidans, did not promote an increase in effective sulfur content in acidified soil and soybean growth, due to the additive effect of the autotrophic nature of A. thiooxidans, soil pH properties, and the inhibition of the growth of A. thiooxidans by the high concentration of monosaccharides secreted by the mycelium of F. mosseae (Fig. 1). This study offers theoretical support for using arbuscular myrhcorizal fungi (AMF) and sulfur-oxidizing bacteria (SOB) as microbial fertilizers in agriculture.