Recently, new biotechnological processes have been developed to enable the sustainable removal of organic and inorganic sulfur compounds from liquid and gaseous hydrocarbon streams. In comparison to existing technologies (e.g., caustic scrubbing or iron based redox technologies) far less chemicals are consumed, while reusable elemental sulfur is formed as the main end-product. This research shows that in these processes a number of consecutive reactions occur between methanethiol (MT) from the hydrocarbon stream and the formed biosulfur particles, leading to the formation of (dimethyl) polysulfides. This is an important feature of this family of new bioprocesses as it improves the MT removal efficiency. The reaction kinetics depend on the MT and biosulfur concentration, temperature, and the nature of the biosulfur particles. The first reaction step involves a S8 ring-opening by nucleophilic attack of MT molecules to form CH3S9(-). This work shows that CH3S9(-) reacts to polysulfides (S3(2-), S4(2-), S5(2-)), dimethyl polysulfides [(CH3)2S2, (CH3)2S3], and dissociated H2S, while also some longer-chain dimethyl polysulfides [(CH3)2S4-7] are formed at μM levels. Control experiments using orthorhombic sulfur flower (S8) did not reveal these reactions.