De-repression and comparison of oil-water separation activity of the dibenzothiophene desulfurizing bacterium, Mycobacterium sp. G3.

Expression of the desulfurization genes (dsz) in Mycobacterium sp. G3 is repressed by sulfate, which is the product of biodesulfurization. An expression clone, pSMTABC, was constructed by placing the dsz genes downstream of the hsp60 promoter and the constructed plasmid was electroporated into G3. The recombinant strain G3-1 desulfurized dibenzothiophene in the presence of 0.5 mM: sulfate while the Dsz phenotype was completely repressed in the wild-type strain. However, there was no significant increase in the amount of desulfurization enzymes in G3-1. In addition, G3 had superior separation of diesel oil-water separation activity compared to E. coli, which is superior to desulfurizing rhodococci.

Analyses of microbial desulfurization reaction of alkylated dibenzothiophenes dissolved in oil phase.

The kinetics of the oil/water two-phase reaction system was analyzed, and the reaction was carried out with the desulfurization of alkylated dibenzothiophenes (Cx-DBTs) using the desulfurizing microorganism Mycobacterium sp. G3. In the water-phase reaction system, the desulfurization activities were constant with respect to species of Cx-DBTs as substrates. However, the desulfurization activities in the oil/water two-phase reaction system against DBT, 4,6-dimethyl DBT, 4,6-diethyl DBT, 4,6-dipropyl DBT, and 4,6-dibutyl DBT were 49.0, 45.9, 11.5, 1.35, and 0.00 micromol g DCW(-1) h(-1), respectively. The kinetic parameters for the degradation of DBT, 4,6-dimethyl DBT, and 4,6-diethyl DBT were also obtained (V(max) values 90.0, 68.7, and 22.7 micromol g DCW(-1) h(-1) and K(m) values 0.21, 0.70, and 3.03 mM, respectively). The reason for the decrease in activity against Cx-DBTs of high molecular weight was a decrease in the V(max) value and an increase in the K(m) value, the latter being a particularly serious problem. Furthermore, the hydrophobicity of the substrate was evaluated as the capacity factor measured by high-performance liquid chromatography (HPLC). The correlation between substrate hydrophobicity and desulfurization activity indicated that the desulfurization reaction in the oil/water two-phase reaction system is greatly influenced by the hydrophobicity of the substrates. In addition, the influence of the solvent on desulfurization activity was examined, and it was found that not only the hydrophobicity of substrates, but also that of solvents, affected the desulfurization reaction.

Functions and potential applications of glycolipid biosurfactants--from energy-saving materials to gene delivery carriers.

Biosurfactants (BS) produced by various microorganisms show unique properties (e.g., mild production conditions, lower toxicity, higher biodegradability and environmental compatibility) compared to their chemical counterparts. The numerous advantages of BS have prompted applications not only in the food, cosmetic, and pharmaceutical industries but in environmental protection and energy-saving technology as well. Glycolipid BS are the most promising, due to high productivity from renewable resources and versatile biochemical properties. Mannosylerythritol lipids (MEL), which are glycolipid BS produced by a yeast Candida antarctrica, exhibit not only excellent interfacial properties but also remarkable differentiation-inducing activities against human leukemia cells. MEL also show a potential anti-agglomeration effect on ice particles in ice slurry used for cold thermal storage. Recently, the cationic liposome bearing MEL has been demonstrated to increase dramatically the efficiency of gene transfection into mammalian cells. These features of BS should broaden its applications in new advanced technologies. The current status of research and development on glycolipid BS, especially their function and potential applications, is discussed.