Isolation and Kinetic Analyses of Bacterial Strains Which Desulfurize Model Compounds Characteristic of Coal

Abstract

Gram positive, aerobic, non-acid fast, non-endospore forming, largely monomorphic rods which convert dibenzothiophene (DBT) or dibenzosulfone (DBTO2) to 2-hydroxybiphenyl (OH-BP) were isolated from soil samples. The identity of the product has been established by fluorometry, colorimetry, UV analysis, HPLC, and mass spectrometry. The desulfurization activity of bacteria (presumptively identified as Rhodococcus erythropolis and having a stable DbtS+ phenotype) has been characterized. With DBTO2 as a sole sulfur source, strain N1-36 has a maximum specific growth rate (μmax) of 0.235 hr−1 (corresponding to a minimum generation time 2.95 hours). The saturation constant (Ks) for DBTO2 was estimated as 0.39 μM; the yield (Yx/s) is 9 mg of biomass / μM of DBTO2. OH-BP is not a carbon source for the isolates nor is the carbon frame of OH-BP altered by the organisms. Batch and fed-batch cultures created with five percent inocula of N1-36 into media having DBT or DBTO2 as sole sulfur source have an exponential growth phase which lasts for approximately 40 hours; DBT (or DBTO2) rapidly disappears, and OH-BP accumulates to concentrations of 40 μM in cultures with DBT and 70 μM with DBTO2. The DbtS+ phenotype is inducible by DBT or DBTO2 and is repressed by SO4=. The desulfurization substrates, DBT and DBTO2, at concentrations up to 200 μM do not inhibit growth whereas the product, OH-BP, inhibits growth at 50 μM. Preliminary data show that the desulfurization activity occur on the surface of N1-36 cells.