The major facilitator superfamily transporter MdtM contributes to intrinsic resistance of Escherichia coli to quaternary ammonium compounds

OBJECTIVES:
Quaternary ammonium compounds (QACs) are used extensively as biocides and their misuse may be contributing to the development of bacterial resistance. Although the major intrinsic resistance to QACs of Gram-negative bacteria is mediated by the action of tripartite multidrug transporters of the resistance-nodulation-division family, we aimed to test if the promiscuity of the recently characterized major facilitator superfamily multidrug transporter, MdtM, from Escherichia coli enabled it also to function in the efflux of QACs.
METHODS:
The ability of the major facilitator mdtM gene product, when overexpressed from multicopy plasmid, to protect E. coli cells from the toxic effects of a panel of seven QACs was determined using growth inhibition assays in liquid medium. Interaction between QACs and MdtM was studied by a combination of substrate binding assays using purified protein in detergent solution and transport assays using inverted vesicles.
RESULTS:
E. coli cells that overproduced MdtM were less susceptible to the cytotoxic effects of each of the QACs tested compared with cells that did not overproduce the transporter. Purified MdtM bound each QAC with micromolar affinity and the protein utilized the electrochemical proton gradient to transport QACs across the cytoplasmic membrane. Furthermore, the results suggested a functional interaction between MdtM and the tripartite resistance-nodulation-division family AcrAB-TolC efflux system.
CONCLUSIONS:
The results support a hitherto unidentified capacity for a single-component multidrug transporter of the major facilitator superfamily, MdtM, to function in the efflux of a broad range of QACs and thus contribute to the intrinsic resistance of E. coli to these compounds.

Reactivity of ammonium chloride/mercuric chloride mixtures with monel containers. The new compounds (NH4)(2)(NH3)(x)[Ni(NH3)(2)Cl-4] and (NH4)(5)Cl-2[CuCl2][CuCl4]

Ammonium chloride/mercuric chloride mixtures (molar ratio 2: 1) react at 350degreesC with Monel (Cu68Ni32) to yield (NH4)NiCl3 and mercury and copper amalgam, respectively. With larger amounts of (NH4)Cl in the reaction mixture, dark green (NH4)(2)(NH3)(x)[Ni(NH3)(2)Cl-4] (x approximate to 0.77) (1) is also formed as a main product. Light blue crystals of the mixed-valent copper(I,II) chloride (NH4)(5)Cl-5[CuCl2][CuCl4] (2) were obtained as a minor byproduct from a 4:1 reaction mixture. The crystal structures were determined from single crystal X-ray data; (1): tetragonal, I4/mmm, a = 770.9(1), e = 794.2(2) pm, 190 reflections, R-1 = 0.0263; (2): tetragonal, I4/mcm, a = 874.8(1), c = 2329.2(3) pm, 451 reflections, R-1 = 0.0736. In (1) Ni2+ resides in trans-[Ni(NH3)(2)Cl-4](2-) octahedra, and in (2) copper(l) is linearly two-coordinated in ECUC121- and copper(II) resides in a flattened tetrahedron [CuCl4](2-) with a tetrahedricity of 89%. (C) 2001 Elsevier Science.

Fate and transport of volatile organic compounds in glacial till and groundwater at an industrial site in Northern Ireland

Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel Monkstown industrial site, Belfast, Northern Ireland. The objectives of this study were to (1) investigate the characteristics of the geological material and its influences on contaminated groundwater flow across the site using borehole logs and hydrological evaluations, and (2) identify the contaminants and examine their distribution in the subsurface geological material and groundwater using chemical analysis. This report focuses on the eastern car park (ECP) which was a former storage area associated with trichloroethene (TCE) degreasing operations. This is where the greatest amount of volatile organic compounds (VOCs), particularly TCE, were detected. The study site is on a complex deposit of clayey glacial till with discontinuous coarser grained lenses, mainly silts, sands and gravel, which occur at 0.45–7.82 m below ground level (bgl). The lenses overall form an elongated formation that acts as a small unconfined shallow aquifer. There is a continuous low permeable stiff clayey till layer beneath the lenses that performs as an aquitard to the groundwater. Highest concentrations of VOCs, mainly TCE, in the geological material and groundwater are in these coarser lenses at ~4.5–7 m bgl. Highest TCE measurements at 390,000 µg L-1 for groundwater and at 39,000 µg kg-1 at 5.7 m for geological material were in borehole GA19 in the coarse lens zone. It is assumed that TCE gained entrance to the subsurface near this borehole where the clayey till was thin to absent above coarse lenses which provided little retardation to the vertical migration of this dense non-aqueous phase liquid (DNAPL) into the groundwater. However, TCE is present in low concentrations in the geological material overlying the coarse lens zone. Additionally, VOCs appear to be associated with poorly drained layers and in peat

Assembly intermediates in polyketide biosynthesis; enantioselective syntheses of beta-hydroxycarbonyl compounds

A versatile approach for the enantioselective synthesis of functionalised beta-hydroxy N-acetylcysteamine thiol esters has been developed which allows the facile incorporation of isotopic labels. It has been shown that a remarkable reversal of selectivity occurs in the titanium mediated aldol reaction of the acyloxazolidone intermediate using either (S)- or (R)-tert-butyldimethylsilyloxybutanal. The aldol products are valuable intermediates in the synthesis of 4-hydroxy-6-substituted gamma-lactones.