Two microbial strains (Brevibacterium sp. DO, Pseudomonas aeruginosa O
S1) were isolated for their ability to desulfurize dibenzothiophene (D
BT) and benzyl methyl sulfide (BMS). Enrichment was achieved by a sulf
ur-selective screening system using the model compounds as the sole so
urce of sulfur for bacterial growth. Brevibacterium sp. DO utilizes DB
T as a sole source of sulfur, carbon and energy for growth, whereas Ps
eudomonas aeruginosa OS1 metabolizes BMS to only a small extent under
sulfur-selective conditions. Investigations of the regulation of enzym
es involved in the desulfurization of coal-relevant sulfur compounds i
ndicate that in nature at least two mechanisms exist: 'carbon regulati
on' and 'sulfur regulation'. The biochemical mechanisms leading to the
desulfurization of BMS and DBT are similar. The sulfur atom of both c
ompounds is initially oxidized to the corresponding sulfone, and cleav
age of the C-S bond proceeds via the formation of a chemically unstabl
e hemimercaptal (S-oxidized form) by oxidation of the carbon atom adja
cent to the sulfur atom. These results indicate that oxidation of sulf
ur to its highest oxidation state may be the precondition for the oxid
ative cleavage of the covalent C-S bonds. By isotope-labelling experim
ents using O-18(2), the initial enzymes were identified as sulfoxygena
ses that use molecular oxygen. Cleavage of the C-S bond of DBT and BMS
leads to the formation of organic sulfinic acids as intermediates. Wi
th DBT the sulfinic acid is desulfurized probably by hydrolysis; this
results in the formation of sulfite and benzoate. The desulfurization
of BMS proceeds by sulfonic acid-oxidation. The applicability of these
biochemical mechanisms to the microbial desulfurization of coal is di
scussed.