Lithoautotrophical oxidation of elemental sulfur by fungi including Fusarium solani isolated from sandstone Angkor temples

Previous study about Fusarium solani THIF01, isolated from deteriorated sandstones of Angkor Wat, Cambodia, has suggested that this fungal strain harbored an endobacterium Bradyrhizobium sp. and oxidized elemental sulfur (S-0) in carbon-free media. Here we eliminated the endobacterium in THIF01 and confirmed that the cured THIF01 retained the ability of chemolithoautotrophic growth on S-0. In addition, thirteen out of eighteen identified fungal strains formed clearing zone on the agarose-solidified basal salts medium containing S-0.F. solani f.sp. pisi NBRC9425 grew in carbon-free liquid medium oxidizing S-0 to thiosulfate and sulfate. Furthermore, we proved that various fungi were capable of growth chemolithotrophically on S-0. An addition of up to 15 mg l(-1) of yeast extract to mineral-salts medium containing S-0 enhanced the production of thiosulfate and sulfate, and higher concentration of yeast extract shifted the metabolism from chemolithotroph to chemoorganotroph. Fungal hyphae were observed to attach to the S-0 granules when growing with less than 100 mg l(-1) yeast extract in the medium, but no such association was evident when incubated with 200 mg l(-1) or more yeast extract. Glucose at concentrations of up to 1 mg l(-1) did not show any negative effect on the sulfur oxidation, indicating there was a threshold concentration of organic compounds affecting the chemolithotrophic growth that has been observed before in the chemolithoautotrophic and chemolithomixotrophic sulfur oxidizing bacteria.