Ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, probed by x-ray reflectivity measurements.

The presence of ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide ([TOMA(+)][C(4)C(4)N(-)]), extending into the bulk from the surface to the depth of approximately 60 A has been probed by x-ray reflectivity measurements. The reflectivity versus momentum transfer (Q) plot shows a broad peak at Q approximately 0.4 A(-1), implying the presence of ionic layers at the [TOMA(+)][C(4)C(4)N(-)] surface. The analysis using model fittings revealed that at least four layers are formed with the interlayer distance of 16 A. TOMA(+) and C(4)C(4)N(-) are suggested not to be segregated as alternating cationic and anionic layers at the [TOMA(+)][C(4)C(4)N(-)] surface. It is likely that the detection of the ionic multilayers with x-ray reflectivity has been realized by virtue of the greater size of TOMA(+) and C(4)C(4)N(-) and the high critical temperature of [TOMA(+)][C(4)C(4)N(-)].

Metabolic engineering for solvent productivity by downregulation of the hydrogenase gene cluster hupCBA in Clostridium saccharoperbutylacetonicum strain N1-4.

The selective production of acetone and butanol is highly desirable from the viewpoint of biofuel production. We have manipulated the activity level of a hydrogenase for this purpose because hydrogen and solvent production are closely correlated with each other. First, we cloned the hydrogenase gene cluster from Clostridium saccharoperbutylacetonicum strain N1-4 and downregulated its expression using an antisense RNA strategy. The cloned hydrogenase gene cluster contained three adjacent open reading frames, designated hupC, hupB, and hupA. Sequence analysis revealed that HupA could accommodate an H-cluster, which is the catalytic domain of the Fe-hydrogenase. HupB and HupC contained no H-cluster but could accommodate several Fe-S clusters. The hupCBA genes were co-transcribed, and the level of the transcript was maximized in the solventogenic phase. When the antisense RNA of the hupC upstream region (180 bp) was expressed under the bdh (encoding butanol dehydrogenase) promoter, significant reduction of hupC translation was observed, indicating that this antisense RNA is effective in strain N1-4. Production of hydrogen in the antisense transformant increased 3.1-fold. Hydrogen-evolving activity was comparable in both the control and antisense strains, but hydrogen uptake activity significantly decreased in the antisense strain (13% remaining). These results indicate that the HupCBA proteins are involved in hydrogen uptake. Importantly, the level of acetone in the antisense transformant increased 1.6-fold, and butanol production decreased to 75.6% compared to the control strain. Thus, we successfully altered solvent productivity by controlling electron flow in an acetone/butanol-producing Clostridium species.

Effects of chloromethanes on growth of and deletion of the pce gene cluster in dehalorespiring Desulfitobacterium hafniense strain Y51.

The dehalorespiring Desulfitobacterium hafniense strain Y51 efficiently dechlorinates tetrachloroethene (PCE) to cis-1,2-dichloroethene (cis-DCE) via trichloroethene by PceA reductive dehalogenase encoded by the pceA gene. In a previous study, we found that the significant growth inhibition of strain Y51 occurred in the presence of commercial cis-DCE. In this study, it turned out that the growth inhibition was caused by chloroform (CF) contamination of cis-DCE. Interestingly, CF did not affect the growth of PCE-nondechlorinating SD (small deletion) and LD (large deletion) variants, where the former fails to transcribe the pceABC genes caused by a deletion of the promoter and the latter lost the entire pceABCT gene cluster. Therefore, PCE-nondechlorinating variants, mostly LD variant, became predominant, and dechlorination activity was significantly reduced in the presence of CF. Moreover, such a growth inhibitory effect was also observed in the presence of carbon tetrachloride at 1 microM, but not carbon dichloride even at 1 mM.