Efficient breaking of water/oil emulsions by a newly isolated de-emulsifying bacterium, Ochrobactrum anthropi strain RIPI5-1.

Water-oil emulsions occur throughout oil production, transportation, and processing. The breaking of the water/oil emulsion improves oil quality and as a consequence chemically synthesized de-emulsifiers are commonly used in the petroleum industries. Microbial de-emulsifiers represent potential alternatives to the chemicals and may become important products for petroleum industries. The main goal of this work was isolation, identification, and characterization of an efficient de-emulsifying bacterium. Following a multi-step enrichment programme a de-emulsifying bacterium, Ochrobactrum anthropi strain RIPI5-1was isolated from the oil-polluted sandy bank of Siri Island, Iran. The presence of an oil phase in growth medium was found to be unnecessary for production of the de-emulsifier. The de-emulsifying activity of both the whole culture and the cells of this strain was examined using a model multiple water-crude oil (w/o/w) emulsion. This w/o/w emulsion was used for the first time in microbial de-emulsification research. Whole cells of strain RIPI5-1 exhibited high de-emulsifying activity during the late-exponential growth and stationary phases; de-emulsifying activity of the whole culture was highest during the early-exponential growth phase. The time course of de-emulsification by whole culture and whole cells of strain RIPI5-1 was investigated; the initial rate (DeI(1)) of breaking of the multiple water-crude oil emulsion by whole culture and whole cells was calculated as 11% and 54%, respectively. However, overall de-emulsification (DeI(8.5)) for whole culture and whole cells was calculated as 63% and 72%, respectively. A clear correlation was observed between cell surface hydrophobicity and the de-emulsifying activity of whole cells. With the water/kerosene emulsion, emulsion half-life (t(1/2)) was found to be <0.5h. The potential activity of this strain was also explained using a complex oilfield emulsion.

Dimethyl sulfoxide (DMSO) as the sulfur source for the production of desulfurizing resting cells of Gordonia alkanivorans RIPI90A.

The sulfate repression of desulfurization (Dsz) phenotype represents a major barrier to the mass production of desulfurizing resting cells. This repression can be avoided by replacing sulfate with dibenzothiophene (DBT) as the main substrate for the 4S pathway. However, mass production of biocatalyst using DBT is impractical because of its high price, low water solubility, and growth inhibition by 2-hydroxybiphenyl (2-HBP), which is the end product of the 4S pathway. In this work, the results showed that readily bioavailable sulfur compounds led to repression of the desulfurization activity of Gordonia alkanivorans RIPI90A. However, the Dsz phenotype was expressed through the 4S pathway in the presence of DMSO as the sulfur source for growth. Resting cells grown on DMSO were more active than the resting cells grown on DBT. The growth rate of strain RIPI90A on DMSO was higher than when DBT was used as the sole sulfur source. DMSO concentration significantly influenced the growth pattern of the strain, and the highest growth rate was observed at a concentration of 200 microg ml(-1). Above this concentration, the growth rate gradually decreased. DBT was found to induce the Dsz phenotype, with no observed lag period, in cells grown on DMSO as the sole sulfur source. Prior to induction, the specific activity was detected as 1.4 micromol 2-HBP (g dry cell weight)(-1) h(-1), and following incubation (5 h) the highest specific activity was observed as 5.11 micromol 2-HBP (g dry cell weight)(-1 )h(-1). This study identified that resting cells can be prepared in a two-step process. First, resting cells can be produced using DMSO as the sulfur source for growth; in the second step, improvements to their desulfurizing activity can be made using DBT as an inducer. DMSO is recommended as an appropriate sulfur source for the mass production of G. alkanivorans RIPI90A.

Stabilization of water/gas oil emulsions by desulfurizing cells of Gordonia alkanivorans RIPI90A.

It has been previously reported that resting-cells, non-proliferating cells, of Gordonia alkanivorans RIPI90A can convert dibenzothiophene (DBT) to 2-hydroxybiphenyl (2-HBP) via the 4S pathway in a biphasic system. The main goal of the current work was to study the behaviour of resting-cells of this strain in biphasic organic media. Resting-cells showed strong affinity for sulfurous organic substrates and were able to stabilize water/gas oil emulsions by attaching to the interface without decreasing the surface tension of their environment. This was consistent with the behaviour of the whole cells but not the surfactants, suggesting that microbial cell-mediated emulsification occurs. It was found that the emulsion-stabilizing activity of the resting-cells was influenced by the growth stage, but was not directly influenced by the metabolic activity of the resting-cells. This activity may be related to cell-surface hydrophobicity, which results from the unique chemical structure of the cell surface. In some biphasic biodesulfurization (BDS) bioreactors, emulsions are created without addition of any surfactant. Cell surface-mediated stabilization helps prolong the emulsions and therefore overcomes mass-transfer limitations in bioreactors. The simultaneous occurrence of emulsion-stabilizing and desulfurization activities of resting-cells was observed for what is believed to be the first time. The results suggest that this strain may have potential for the BDS of diesel oils.