In situ magnetic separation and immobilization of dibenzothiophene-desulfurizing bacteria

In situ cell separation and immobilization of bacterial cells for biodesulfurization were developed by using superparamagnetic Fe₃O₄ nanoparticles (NPs). The Fe₃O₄ NPs were synthesized by coprecipitation followed by modification with ammonium oleate. The surface-modified NPs were monodispersed and the particle size was about 13 nm with 50.8 emu/g saturation magnetization. After adding the magnetic fluids to the culture broth, Rhodococcus erythropolis LSSE8-1 cells were immobilized by adsorption and then separated with an externally magnetic field. The maximum amount of cell mass adsorbed was about 530 g dry cell weight/g particles to LSSE8-1 cells. Analysis showed that the nanoparticles were strongly absorbed to the surface and coated the cells. Compared to free cells, the coated cells not only had the same desulfurizing activity but could also be easily separated from fermentation broth by magnetic force. Based on the adsorption isotherms and Zeta potential analysis, it was believed that oleate-modified Fe₃O₄ NPs adsorbed bacterial cells mainly because of the nano-size effect and hydrophobic interaction.     

Evidence for the role of zinc on the performance of dibenzothiophene desulfurization by <Emphasis Type="Italic">Gordonia alkanivorans</Emphasis> strain 1B

Gordonia alkanivorans strain 1B is able to desulfurize dibenzothiophene (DBT) to 2-hydroxybiphenyl (2-HBP), the final product of the 4S pathway. However, both the cell growth and the rate of desulfurization can be largely affected by the nutrient composition of the growth medium due to cofactor requirements of many enzymes involved in the biochemical pathways. In this work, the effect of several metal ions on the growth and DBT desulfurization by G. alkanivorans was studied. From all the metal ions tested, only the absence of zinc significantly affected the cell growth and the desulfurization rate. By increasing the concentration of Zn from 1 to 10 mg L⁻¹, 2-HBP productivity was improved by 26%. The absence of Zn²⁺, when sulfate was also used as the only sulfur source, did not cause any difference in the bacterial growth. Resting cells grown in the presence of Zn²⁺ exhibited a 2-HBP specific productivity of 2.29 μmol g⁻¹ (DCW) h⁻¹, 7.6-fold higher than the specific productivity obtained by resting cells grown in the absence of Zn²⁺ (0.30 μmol g⁻¹ (DCW) h⁻¹). These data suggests that zinc might have a key physiological role in the metabolism of DBT desulfurization.     

微生物脱有机硫研究前沿

环境问题日益成为人们关注的焦点,现代工业的发展使人类对化石燃料的依赖性越来越大。化石燃料的大量使用也造成了环境的严重污染,常规的加氢法处理燃油能耗高,处理效果不理想等方面的缺陷促进了生物脱硫的研究。简述了国外过去三年来在生物脱硫工作中取得的进展,包括菌株的改造;单加氧酶活力必需的黄素还原酶DszD;途径的最后一个酶HPBS脱硫酶以及国外公司的一些工作。     

Biodegradation of carbazole in oil/water biphasic system by a newly isolated bacterium Klebsiella sp. LSSE-H2

A novel Klebsiella sp. strain LSSE-H2 (CGMCC No. 1624) was isolated from dye-contaminated soil based on its ability to metabolize carbazole as a sole source of carbon and nitrogen. This strain efficiently degraded carbazole from either aqueous and biphasic aqueous–organic media, displaying a high denitrogenation activity and a high level of solvent tolerance. LSSE-H2 could completely degrade 12 mmol/L carbazole after 56 h of cultivation. The co-culture of LSSE-H2 and Pseudomonas delafieldii R-8 strains can degrade approximately 92% of carbazole (10 mmol/L) and 94% of dibenzothiophene (3 mmol/L) from model diesel in 12 h.     

Biodesulfurization of dibenzothiophene by a newly isolated Rhodococcus erythropolis strain

A new dibenzothiophene (DBT) desulfurizing bacterium was isolated from oil-contaminated soils in Iran. HPLC analysis and PCR-based detection of the presence of the DBT desulfurization genes (dszA, dszB and dszC) indicate that this strain converts DBT to 2-hydroxybiphenyl (2-HBP) via the 4S pathway. The strain, identified as Rhodococcus erythropolis SHT87, can utilize DBT, dibenzothiophene sulfone, thiophene, 2-methylthiophene and dimethylsulfoxide as a sole sulfur source for growth at 30 °C.The maximum specific desulfurization activity of strain SHT87 resting cells in aqueous and biphasic organic–aqueous systems at 30 °C was determined to be 0.36 and 0.47 μmol 2-HBP min⁻¹ (g dry cell)⁻¹, respectively. Three mM DBT was completely metabolized by SHT87 resting cells in the aqueous and biphasic systems within 10 h. The rate and the extent of the desulfurization reaction by strain SHT87 suggest that this strain can be used for the biodesulfurization of diesel oils.     

红球菌SDUZAWQ对有机硫和无机硫的耐受性研究及脱硫基因的克隆

以筛选得到的红球菌SDUZAWQ为对象,研究其在不同浓度的有机硫化合物二苯并噻吩(DBT)存在下的脱硫能力,以及在0.2mmolLDBT和不同浓度Na2SO4同时存在下的脱硫情况。当DBT浓度高达6mmolL时,菌株仍能生长,而且检测出产物2-羟基联苯(2-HBP)的存在,说明该菌株具有耐受较高浓度DBT的能力。当DBT和Na2SO4同时存在时,DBT为菌株SDUZAWQ所利用,并且也检测出2-HBP,并非如文献所报道的红球菌在无机硫存在下不代谢DBT,表明该菌株能够耐受一定浓度的无机硫酸盐。对相关脱硫基因的克隆和测序结果显示,完整脱硫基因dszABC、其上游调控序列和dszD的序列与模式菌株RhodococcuserythropolisIGTS8的同源性分别是99%、100%和100%。     

脱硫菌Fds-1的分离鉴定及其对柴油脱硫特性的研究

从含硫土壤中分离筛选出一株专一性脱硫菌Fds-1,经生理生化指标和16S rRNA序列分析鉴定其属于枯草芽孢杆菌(Bacillus subtilis)。用Gibb’s试剂显色和气相色谱-质谱联用分析表明,该菌株通过“4S”途径脱除有机硫。实验发现Fds-1的最佳脱硫活性在30℃,在此温度下72h内能脱除约0.5mmol/L DBT中的有机硫。Fds-1菌株对有机硫化合物的利用情况和柴油脱硫前后烃组分比较都进一步证明该菌株适合于柴油生物脱硫。利用休止细胞对不同组分柴油的脱硫研究表明,脱硫菌株Fds-1对精制柴油中的DBT类化合物的降解能力强。因此,该菌株对精制低硫柴油的深度脱硫具有应用意义。     

Enhanced dibenzothiophene biodesulfurization in a microchannel reactor

A microchannel reactor system was used in a biodesulfurization process in which the rate of biodesulfurization in the oil/water phase of the microchannel reaction was more than nine-fold that in a batch (control) reaction. In addition, the microchannel reaction system using a bacterial cell suspension degraded alkylated dibenzothiophene that was not degraded by the batch reaction system. This work provides a foundation for the application of a microchannel reactor system consisting of biological catalysts using an oil/water phase reaction.     

Improvement of biodesulfurization activity of alginate immobilized cells in biphasic systems

The immobilization of Pseudomonas delafieldii R-8 in calcium alginate beads has been studied in order to improve biodesulfurization activity in oil/water (O/W) biphasic systems. A gas jet extrusion technique was performed to produce immobilized beads. The specific desulfurization rate of 1.5 mm diameter beads was 1.4-fold higher than that of 4.0 mm. Some nonionic surfactants can significantly increase the activity of immobilized cells. The desulfurization rate with the addition of 0.5% Span 80 increased 1.8-fold compared with that of the untreated beads. The rate of biodesulfurization was markedly enhanced by decreasing the size of alginate beads and adding the surfactant Span 80, most likely resulting from the increasing mass transfer of substrate to gel matrix.     

In vivo evolution of the Rhodococcus sp. strain DS7: selection of recombinants able to desulfurize both dibenzothiophene and benzothiophene

Rhodococcus sp. DS7, isolated from a polluted soil, has shown good desulfurizing activity towards dibenzothiophene (DBT) and its derivatives, but is not able to desulfurize benzothiophene (BT), the other thiophenic molecule recalcitrant to the chemical hydrodesulfurization (HDS) process, and most abundant in gasoline. To select a Rhodococcus DS7 derivative strain able to desulfurize both DBT and BT, we took advantage of the verified capacity of this strain to integrate exogenous DNA randomly, with a good efficiency. Heterologous chromosomal DNA, digested with restriction enzymes, from two BT but not DBT desulfurizing strains, Rhodococcus sp. ATCC 27778 and Gordonia sp. ATCC 19067, was electroporated into Rhodococcus DS7. Selection on minimal medium with BT as sole sulfur source allowed us to isolate several DS7 derivatives with the capacity to desulfurize both thiophenic molecules. Two strains, one derived from the integration and recombination of DNA from ATCC 27778, and the other from ATCC 19067, have been partially characterized. These recombinant microorganisms are an interesting starting point to develop new biodesulfurization processes.