Insights into the Superior Bioavailability of Biogenic Sulfur from the View of Its Unique Properties: The Key Role of Trace Organic Substances

Elemental sulfur (S⁰) is widely utilized in environmental pollution control, while its low bioavailability has become a bottleneck for S⁰-based biotechnologies. Biogenic sulfur (bio-S⁰) has been demonstrated to have superior bioavailability, while little is known about its mechanisms thus far. This study investigated the bioavailability and relevant properties of bio-S⁰ based on the denitrifying activity of Thiobacillus denitrificans with chemical sulfur (chem-S⁰) as the control. It was found that the conversion rate and removal efficiency of nitrate in the bio-S⁰ system were 2.23 and 2.04 times those of the chem-S⁰ system. Bio-S⁰ was not pure orthorhombic sulfur [S: 96.88 ± 0.25% (w/w)]. Trace organic substances detected on the bio-S⁰ surface were revealed to contribute to its hydrophilicity, resulting in better dispersibility in the aqueous liquid. In addition, the adhesion force of T. denitrificans on bio-S⁰ was 1.54 times that of chem-S⁰, endowing a higher bacterial adhesion efficiency on the sulfur particle. The weaker intermolecular binding force due to the low crystallinity of bio-S⁰ led to enhanced cellular uptake by attached bacteria. The mechanisms for the superior bioavailability of bio-S⁰ were further proposed. This study provides a comprehensive view of the superior bioavailability of bio-S⁰ and is beneficial to developing high-quality sulfur resources.