| Vast amounts of sulfur oxides released into the atmosphere by combustion of fossil fuels are the principal sources of acid rain. High sulfur contents of the crude oil reserves, the need for fuels ultra-low in sulfur and continued stringent regulations call for deep desulfurization technologies. Biodesulfurization (BDS) offers an attractive alternative or may be used complementary to hydrodesulfurization (HDS) due to the mild operating conditions, low costs and great reaction specificity afforded by the nature of biocatalysis. In the present work, BDS was studied with a newly isolated bacterial strain Microbacterium sp. ZD-M2.Seven bacterial strains capable of converting dibenzothiophene into 2-hydroxybiphenyl by cleaving the carbon-sulfur bonds were isolated from sludge and soil samples. Among them two strains, numbered 2# and 7# , were chosen for further characterization because of their relatively high desulfurization activities. Their growth curves were investigated under the condition of 30 ℃, PH 7.0, 0.5 mmol·L-1DBT as the sole sulfur-source, glycerol as carbon nutrient in shaking flask. Other organic sulfur compounds such as thiophene, benzothiophene, diphenylsulfid and 4,6-dimenthylDBT, can also be used as sulfur sources to growth by the two strains, showing a broad substrate range. Strain 2# is chosen for further study since the desulfurization activity of strain 2 was better than that of strain 7# . This organism, designated ZD-M2, clustered most closely with members of the genus Microbacterium, as determined by 16S rRNA gene sequence analysis, and was firstly found to our knowledge.In aqueous the strain grew well in the pH range of 6.59.5, the optimal temperature for growth was 30 ℃. Though organic nitrogen was better than inorganic nitrogen for strain growth, it inhibited the desulfurization activity, and the appropriate concentration of ammonium chloride as the source of nitrogen was 1.0 g·L-1. Glycerol and DBT were selected as the best carbon and sulfur sources for its growth, and the optimal concentration and amount were 2.0 g·L-1 and 0.5 mmol·L-1, respectively. Desulfurization ability was studied in the presence of hexadecane as model oil with an optimal volume ratio of oil-to-aqueous of 1:1. In the aqueous and model oil-aqueous system, the desulfurization activities of strain ZD-M2 and 7# were compared. It showed that the presence of hexadecane enhanced the activity of desulfurization, however the stability of the desulfurizing activity was worse than that in aqueous.Metabolites produced by DBT desulfurization were identified by GC-MS, and two sulfur-free products, 2-methoxybiphenyl (2-MBP) and biphenyl, were detected in addition to 2-hydroxybiphenyl (2-HBP), the end product of the previously reported sulfur-specific pathway (also called 4S pathway). The results suggest that the production of 2-MBP and biphenyl has the advantage of partially eliminating the inhibitory effect of 2-HBP and the pollution from diesel oil combustion. Not only the growth of ZD-M2, but the production and the activity of desulfurization enzyme were inhibited by 2-HBP. In aqueous phase, the degradation of DBT was stopped with a degradated amount of 25% once the concentration of 2-HBP was above 0.1 mM,however, when the concentration of 2-HBP was above 0.2 mM, the amount of degradated DBT was 50%. It showed the presence of hexadecane effectively eliminated the inhibitory of 2-HBP. Kinetic model of product (2-HBP) formation have firstly been attempted to develop. The model was found to meet Garden's growth-associated scheme, i.e. 2-HBP is reffered to as growth-associated product, its rate of production parallels the growth of the cell population.Biodesulfurization of DBT by strain ZD-M2 in an oil-aqueous system was carried out in a self-designed airlift bioreactor. The optimal gas volume was 180 L·h-1. The desulfurization of resting cells of ZD-M2 could be proceeded in the non-growth media (saline and phosphate buffer) as efficiently as in the growth medium (BSM). In aqueous system, the concentration of...
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