Influence of hydrophobicity distribution of particle mixtures on emulsion stabilization.

Whilst emulsions stabilized by uniform particles are well established, the emulsification behavior of heterogeneous mixtures of particles with varying hydrophobicity is rarely examined. Consequently, the influence of the distribution of particle hydrophobicity on oil-water emulsion stabilization is poorly understood. In the present work, the wettability of the bitumen froth fine solids from Alberta oil sands was studied by film flotation and toluene-water emulsification tests, before and after a hydrothermal treatment at 300-420°C. This approach provided a series of populations of particles with different distributions of hydrophobicity. The initial fine particles in the bitumen froth had a critical surface tension ranging from 26 to 56mN/m, with a mean value of 39mN/m. Hydrothermal treatment at 300-420°C progressively shifted the hydrophobicity distribution of the fine particles, resulting in a lower mean critical surface tension and a narrower critical surface tension range. The emulsifying capacity of the fine particle mixtures, as indicated by the volume of the produced toluene-water emulsions, was unrelated to the mean critical surface tension. Instead, emulsification depended on the proportion of a specific sub-fraction of particles with a critical surface tension of 27-30mN/m. This sub-fraction of particles, with intermediate hydrophobicity, dominated the emulsification behavior of the particle mixtures.

Steroid-Derived Naphthoquinoline Asphaltene Model Compounds: Hydriodic Acid Is the Active Catalyst in I2-Promoted Multicomponent Cyclocondensation Reactions.

A multicomponent cyclocondensation reaction between 2-aminoanthracene, aromatic aldehydes, and 5-α-cholestan-3-one has been used to synthesize model asphaltene compounds. The active catalyst for this reaction has been identified as hydriodic acid, which is formed in situ from the reaction of iodine with water, while iodine is not a catalyst under anhydrous conditions. The products, which contain a tetrahydro[4]helicene moiety, are optically active, and the stereochemical characteristics have been examined by VT-NMR and VT-CD spectroscopies, as well as X-ray crystallography.

Scalable, chromatography-free synthesis of alkyl-tethered pyrene-based materials. Application to first-generation "archipelago model" asphaltene compounds.

In this paper, we report a highly efficient, scalable approach to the total synthesis of conformationally unrestricted, electronically isolated arrays of alkyl-tethered polycyclic aromatic chromophores. This new class of modular molecules consists of polycyclic aromatic "islands" comprising significant structural fragments present in unrefined heavy petroleum, tethered together by short saturated alkyl chains, as represented in the "archipelago model" of asphaltene structure. The most highly branched archipelago compounds reported here share an architecture with first-generation dendrimeric constructs, making the convergent, chromatography-free synthesis described herein particularly attractive for further extensions in scope and applications to materials chemistry. The syntheses are efficient, selective, and readily adaptable to a multigram scale, requiring only inexpensive, "earth-abundant" transition-metal catalysts for cross-coupling reactions and extraction and fractional crystallization for purification. This approach avoids typical limitations in cost, scale, and operational practicality. All of the archipelago compounds and synthetic intermediates have been fully characterized spectroscopically and analytically. The solid-state structure of one archipelago model compound has been determined by X-ray crystallography.

New vanadium compounds in Venezuela heavy crude oil detected by positive-ion electrospray ionization fourier transform ion cyclotron resonance mass spectrometry.

Metalloporphyrins are ubiquitous in nature, particularly iron porphyrins (hemes) and magnesium dihydroporphyrins or chlorophylls. Oxovanadium (IV) complexes of alkyl porphyrins are widely distributed in petroleum, oil shales and maturing sedimentary bitumen. Here we identify new vanadium compounds in Venezuela Orinoco heavy crude oil detected by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). These compounds likely have the main structure of porphyrin, with the addition of more aromatic rings, thiophene and amino functional groups, corresponding to molecular series of C(n)H(2n-40)N(4)V(1)O(1) (36 ≤ n ≤ 58),C(n)H(2n-42)N(4)V(1)O(1) (37 ≤ n ≤ 57),C(n)H(2n-44)N(4)V(1)O(1) (38 ≤ n ≤ 59),C(n)H(2n-46)N(4)V(1)O(1) (43 ≤ n ≤ 54),C(n)H(2n-48)N(4)V(1)O(1) (45 ≤ n ≤ 55),C(n)H(2n-38)N(4)V(1)S(1)O(1) (36 ≤ n ≤ 41),C(n)H(2n-40)N(4)V(1)S(1)O(1) (35 ≤ n ≤ 51),C(n)H(2n-42)N(4)V(1)S(1)O(1) (36 ≤ n ≤ 54),C(n)H(2n-44)N(4)V(1)S(1)O(1) (41 ≤ n ≤ 55),C(n)H(2n-46)N(4)V(1)S(1)O(1) (39 ≤ n ≤ 55),C(n)H(2n-27)N(5)V(1)O(1) (29 ≤ n ≤ 40),C(n)H(2n-29)N(5)V(1)O(1) (34 ≤ n ≤ 42),C(n)H(2n-33)N(5)V(1)O(1) (31 ≤ n ≤ 38),C(n)H(2n-35)N(5)V(1)O(1) (32 ≤ n ≤ 41),C(n)H(2n-27)N(5)V(1)O(2) (32 ≤ n ≤ 41) and C(n)H(2n-29)N(5)V(1)O(2) (33 ≤ n ≤ 42). These findings are significant for the understanding of the existing form of vanadium species in nature, and are helpful for enhancing the amount of information on palaeoenvironments and improving the level of applied basic theory for the processing technologies of heavy oils.

Evaluating steady-state and time-resolved fluorescence as a tool to study the behavior of asphaltene in toluene.

A combination of steady-state fluorescence, fluorescence lifetime measurements and the determination of time-resolved emission spectra were employed to characterize asphaltene toluene solutions. Lifetime measurements were shown to be insensitive to the source of asphaltene or the alkane solvent from which asphaltene was precipitated. This insensitivity suggests that either the composition of Athabasca and Cold Lake asphaltene is very similar or that the fluorescence behavior is dominated by the same sub-set of fluorophores for the different samples. These results highlight the limitations in using fluorescence to characterize asphaltene solutions. Different dependencies were observed for the average lifetimes with the asphaltene concentration when measured at two different emission wavelengths (420 nm and 520 nm). This result suggests that different fluorophores underwent diverse interactions with other asphaltene molecules as the asphaltene concentration was raised, suggesting that models for asphaltene aggregation need to include molecular diversity.

The EmhABC efflux pump decreases the efficiency of phenanthrene biodegradation by Pseudomonas fluorescens strain LP6a.

Pseudomonas fluorescens strain LP6a, designated here as strain WEN (wild-type PAH catabolism, efflux positive), utilizes the polycyclic aromatic hydrocarbon phenanthrene as a carbon source but also extrudes it into the extracellular medium using the efflux pump EmhABC. Because phenanthrene is considered a nontoxic carbon source for P. fluorescens WEP, its energy-dependent efflux seems counter-productive. We hypothesized that the efflux of phenanthrene would decrease the efficiency of its biodegradation. Indeed, an emhB disruptant strain, wild-type PAH catabolism, efflux negative (WEN), biodegraded 44% more phenanthrene than its parent strain WEP during a 6-day incubation. To determine whether efflux affected the degree of oxidation of phenanthrene, we quantified the conversion of ¹4C-phenanthrene to radiolabeled polar metabolites and ¹4CO2. The emhB⁻ WEN strain produced approximately twice as much ¹4CO2 and radiolabeled water-soluble metabolites as the WEP strain. In contrast, the mineralization of ¹4C-glucose, which is not a known EmhB efflux substrate, was equivalent in both strains. An early open-ring metabolite of phenanthrene, trans-4-(1-hydroxynaphth-2-yl)-2-oxo-3-butenoic acid, also was found to be a substrate of the EmhABC pump and accumulated in the supernatant of WEP but not WEN cultures. The analogous open-ring metabolite of dibenzothiophene, a heterocyclic analog of phenanthrene, was extruded by EmhABC plus a putative alternative efflux pump, whereas the end product 3-hydroxy-2-formylbenzothiophene was not actively extruded from either WEP or WEN cells. These results indicate that the active efflux of phenanthrene and its early metabolite(s) decreases the efficiency of phenanthrene degradation by the WEP strain. This activity has implications for the bioremediation and biocatalytic transformation of polycyclic aromatic hydrocarbons and heterocycles.

Adhesion to the hydrocarbon phase increases phenanthrene degradation by Pseudomonas fluorescens LP6a.

Microbial adhesion is an important factor that can influence biodegradation of poorly water soluble hydrocarbons such as phenanthrene. This study examined how adhesion to an oil-water interface, as mediated by 1-dodecanol, enhanced phenanthrene biodegradation by Pseudomonas fluorescens LP6a. Phenanthrene was dissolved in heptamethylnonane and added to the aerobic aqueous growth medium to form a two phase mixture. 1-Dodecanol was non-toxic and furthermore could be biodegraded slowly by this strain. The alcohol promoted adhesion of the bacterial cells to the oil-water interface without significantly changing the interfacial or surface tension. Introducing 1-dodecanol at concentrations from 217 to 4,100 mg l(-1) increased phenanthrene biodegradation by about 30% after 120 h incubation. After 100 h incubation, cultures initially containing 120 or 160 mg l(-1) 1-dodecanol had mineralized >10% of the phenanthrene whereas those incubated without 1-dodecanol had mineralized only 4.5%. The production and accumulation of putative phenanthrene metabolites in the aqueous phase of cultures likewise increased in response to the addition of 1-dodecanol. The results suggest that enhanced adhesion of bacterial cells to the oil-water interface was the main factor responsible for enhanced biodegradation of phenanthrene to presumed polar metabolites and to CO(2).

Selective sorting of cargo proteins into bacterial membrane vesicles.

In contrast to the well established multiple cellular roles of membrane vesicles in eukaryotic cell biology, outer membrane vesicles (OMV) produced via blebbing of prokaryotic membranes have frequently been regarded as cell debris or microscopy artifacts. Increasingly, however, bacterial membrane vesicles are thought to play a role in microbial virulence, although it remains to be determined whether OMV result from a directed process or from passive disintegration of the outer membrane. Here we establish that the human oral pathogen Porphyromonas gingivalis has a mechanism to selectively sort proteins into OMV, resulting in the preferential packaging of virulence factors into OMV and the exclusion of abundant outer membrane proteins from the protein cargo. Furthermore, we show a critical role for lipopolysaccharide in directing this sorting mechanism. The existence of a process to package specific virulence factors into OMV may significantly alter our current understanding of host-pathogen interactions.

Molecular- and cultivation-based analyses of microbial communities in oil field water and in microcosms amended with nitrate to control H2S production.

Nitrate injection into oil fields is an alternative to biocide addition for controlling sulfide production ('souring') caused by sulfate-reducing bacteria (SRB). This study examined the suitability of several cultivation-dependent and cultivation-independent methods to assess potential microbial activities (sulfidogenesis and nitrate reduction) and the impact of nitrate amendment on oil field microbiota. Microcosms containing produced waters from two Western Canadian oil fields exhibited sulfidogenesis that was inhibited by nitrate amendment. Most probable number (MPN) and fluorescent in situ hybridization (FISH) analyses of uncultivated produced waters showed low cell numbers (≤10(3) MPN/ml) dominated by SRB (>95% relative abundance). MPN analysis also detected nitrate-reducing sulfide-oxidizing bacteria (NRSOB) and heterotrophic nitrate-reducing bacteria (HNRB) at numbers too low to be detected by FISH or denaturing gradient gel electrophoresis (DGGE). In microcosms containing produced water fortified with sulfate, near-stoichiometric concentrations of sulfide were produced. FISH analyses of the microcosms after 55 days of incubation revealed that Gammaproteobacteria increased from undetectable levels to 5-20% abundance, resulting in a decreased proportion of Deltaproteobacteria (50-60% abundance). DGGE analysis confirmed the presence of Delta- and Gammaproteobacteria and also detected Bacteroidetes. When sulfate-fortified produced waters were amended with nitrate, sulfidogenesis was inhibited and Deltaproteobacteria decreased to levels undetectable by FISH, with a concomitant increase in Gammaproteobacteria from below detection to 50-60% abundance. DGGE analysis of these microcosms yielded sequences of Gamma- and Epsilonproteobacteria related to presumptive HNRB and NRSOB (Halomonas, Marinobacterium, Marinobacter, Pseudomonas and Arcobacter), thus supporting chemical data indicating that nitrate-reducing bacteria out-compete SRB when nitrate is added.

Structures of water molecules at solvent/silica interfaces.

The adsorption of water at solvent/silica interfaces was studied using IR-visible sum frequency generation (SFG) vibrational spectroscopy. We discovered a water layer between toluene and silica with no detectable free OHs. The water layer without free OHs showed resistance against further adsorption of water molecules. This "water-resistant" water surface was very stable at room temperature and did not become a regular water layer with free OH over a period of 12 h in water-saturated toluene. However, this special structure of water was not observed at heptane/silica interfaces, at which free OHs were observed. The study indicates that interactions between solvents and water molecules can significantly change the interfacial water properties.

Application of atomic force microscopy in bacterial research.

The atomic force microscope (AFM) has evolved from an imaging device into a multifunctional and powerful toolkit for probing the nanostructures and surface components on the exterior of bacterial cells. Currently, the area of application spans a broad range of interesting fields from materials sciences, in which AFM has been used to deposit patterns of thiol-functionalized molecules onto gold substrates, to biological sciences, in which AFM has been employed to study the undesirable bacterial adhesion to implants and catheters or the essential bacterial adhesion to contaminated soil or aquifers. The unique attribute of AFM is the ability to image bacterial surface features, to measure interaction forces of functionalized probes with these features, and to manipulate these features, for example, by measuring elongation forces under physiological conditions and at high lateral resolution (<1 A). The first imaging studies showed the morphology of various biomolecules followed by rapid progress in visualizing whole bacterial cells. The AFM technique gradually developed into a lab-on-a-tip allowing more quantitative analysis of bacterial samples in aqueous liquids and non-contact modes. Recently, force spectroscopy modes, such as chemical force microscopy, single-cell force spectroscopy, and single-molecule force spectroscopy, have been used to map the spatial arrangement of chemical groups and electrical charges on bacterial surfaces, to measure cell-cell interactions, and to stretch biomolecules. In this review, we present the fascinating options offered by the rapid advances in AFM with emphasizes on bacterial research and provide a background for the exciting research articles to follow.

Computational and experimental study of the structure, binding preferences, and spectroscopy of nickel(II) and vanadyl porphyrins in petroleum.

We present a computational exploration of five- and six-coordinate Ni(II) and vanadyl porphyrins, including prediction of UV-vis spectroscopic behavior and metalloporphyrin structure as well as determination of a binding energy threshold between strongly bound complexes that have been isolated as single crystals and weakly bound ones that we detect by visible absorption spectroscopy. The excited states are calculated using the tandem of the time-dependent density functional theory (TD-DFT) and the conductor-like polarizable continuum model (CPCM). The excited-state energies in chloroform solvent obtained by using two density functionals are found to correlate linearly with the experimental Soret and alpha-band energies for a known series of five-coordinate vanadyl porphyrins. The established linear correction allows simulation of the excited states for labile octahedral vanadyl porphyrins that have not been isolated and yields Soret and alpha-band bathochromic shifts that are in agreement with our UV-vis spectroscopic results. The PBE0 and PW91 functionals in combination with DNP basis set perform best for both structure and binding energy prediction. The reactivity preferences of Ni(II) and vanadyl porphyrins toward aromatic fragments of large petroleum molecules are explored by using the density functional theory (DFT). Analysis of electrostatic potentials and Fukui functions matching shows that axial coordination and hydrogen bonding are the preferred aggregation modes between vanadyl porphyrins and nitrogen-containing heterocycle fragments. This investigation improves our understanding on the cause for broadening of the Ni and V porphyrin Soret band in heavy oils. Our findings can be useful for the development of metals removal methods for heavy oil upgrading.

Sulfide persistence in oil field waters amended with nitrate and acetate.

Nitrate amendment is normally an effective method for sulfide control in oil field-produced waters. However, this approach has occasionally failed to prevent sulfide accumulation, despite the presence of active nitrate-reducing bacterial populations. Here, we report our study of bulk chemical transformations in microcosms of oil field waters containing nitrate-reducing, sulfide-oxidizing bacteria, but lacking denitrifying heterotrophs. Amendment with combinations of nitrate, acetate, and phosphate altered the microbial sulfur and nitrogen transformations. Elemental sulfur produced by chemotrophic nitrate-reducing bacteria was re-reduced heterotrophically to sulfide. Ammonification, rather than denitrification, was the predominant pathway for nitrate reduction. The application of nitrite led to transient sulfide depletion, possibly due to higher rates of nitrite reduction. The addition of molybdate suppressed both the accumulation of sulfide and the heterotrophic reduction of nitrate. Therefore, sulfidogenesis was likely due to elemental sulfur-reducing heterotrophic bacteria, and the nitrate-reducing microbial community consisted mainly of facultatively chemotrophic microbes. This study describes one set of conditions for continued sulfidogenesis during nitrate reduction, with important implications for nitrate control of sulfide production in oil fields.

Analysis of force interactions between AFM tips and hydrophobic bacteria using DLVO theory.

Microbial adhesion to surfaces and interfaces is strongly influenced by their structure and physicochemical properties. We used atomic force microscopy (AFM) to measure the forces between chemically functionalized AFM tips and two bacterial species exhibiting different cell surface hydrophobicities, measured as the oil/water contact angle (theta): Acinetobacter venetianus RAG-1 (theta = 56.4 degrees ) and Rhodococcus erythropolis 20S-E1-c (theta = 152.9 degrees ). The forces were measured as the AFM tips, coated with either hydrophobic (octadecane) or hydrophilic (undecanol) groups, approached the bacterial cells in aqueous buffer. The experimental force curves between the two microbial cells and functionalized AFM probes were not successfully described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloid stability. To reconcile the discrepancy between theory and experiments, two types of extended DLVO models were proposed. The first modification considers an additional acid-base component that accounts for attractive hydrophobic interactions and repulsive hydration effects. The second model considers an additional exponentially decaying steric interaction between polymeric brushes in addition to the acid-base interactions. These extended DLVO predictions agreed well with AFM experimental data for both A. venetianus RAG-1, whose surface consists of an exopolymeric capsule and pili, and R. erythropolis 20S-E1-c, whose surface is covered by an exopolymeric capsule. The extended models for the bacteria-AFM tip force-distance curves were consistent with the effects of steric interactions.

Hydrophobic bacteria at the hexadecane-water interface: examination of micrometre-scale interfacial properties.

Hydrophobic bacteria, like colloidal solids, can spontaneously adsorb onto fluid-fluid interfaces and modify their mechanical properties. In this study, two strains of bacteria--Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c--were prepared in their stationary (i.e. non-dividing) phase in the absence of biosurfactants; the cells were then used as emulsifiers to stabilize n-hexadecane droplets in aqueous environments. Using the micropipette technique, colloidal stability of the bacteria-coated droplets was examined through direct-contact experiments. Both types of bacteria were seen to function as effective stabilizers, although the Acinetobacter venetianus RAG-1 film provided stronger resistance to droplet-droplet coalescence. In addition to creating steric barriers, the adsorbed bacteria also interacted with one another at the interface, giving rise to higher order rheological properties. A technique of directly probing the mechanical properties of the emulsion drop surfaces (i.e. the adsorbed films) on the micrometre-scale revealed that (a) the films behaved as purely elastic sheets, and (b) with a reduction in cell concentration in the aqueous phase, less oil was emulsified, but the elastic moduli of the adsorbed films remained unchanged (suggesting an "all or none" adsorption process). These results are in contrast to a previous macroscopic (i.e. millimetre-scale) study, which showed that the absorbed films were viscoelastic, with the apparent elastic moduli depending strongly on cell concentration. The rheological properties of these bacteria-adsorbed interfaces appeared therefore to be length scale-dependent.

Atomic force microscopy measurement of heterogeneity in bacterial surface hydrophobicity.

The structure and physicochemical properties of microbial surfaces at the molecular level determine their adhesion to surfaces and interfaces. Here, we report the use of atomic force microscopy (AFM) to explore the morphology of soft, living cells in aqueous buffer, to map bacterial surface heterogeneities, and to directly correlate the results in the AFM force-distance curves to the macroscopic properties of the microbial surfaces. The surfaces of two bacterial species, Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c, showing different macroscopic surface hydrophobicity were probed with chemically functionalized AFM tips, terminating in hydrophobic and hydrophilic groups. All force measurements were obtained in contact mode and made on a location of the bacterium selected from the alternating current mode image. AFM imaging revealed morphological details of the microbial-surface ultrastructures with about 20 nm resolution. The heterogeneous surface morphology was directly correlated with differences in adhesion forces as revealed by retraction force curves and also with the presence of external structures, either pili or capsules, as confirmed by transmission electron microscopy. The AFM force curves for both bacterial species showed differences in the interactions of extracellular structures with hydrophilic and hydrophobic tips. A. venetianus RAG-1 showed an irregular pattern with multiple adhesion peaks suggesting the presence of biopolymers with different lengths on its surface. R. erythropolis 20S-E1-c exhibited long-range attraction forces and single rupture events suggesting a more hydrophobic and smoother surface. The adhesion force measurements indicated a patchy surface distribution of interaction forces for both bacterial species, with the highest forces grouped at one pole of the cell for R. erythropolis 20S-E1-c and a random distribution of adhesion forces in the case of A. venetianus RAG-1. The magnitude of the adhesion forces was proportional to the three-phase contact angle between hexadecane and water on the bacterial surfaces.

Aerobic biotransformation of decalin (decahydronaphthalene) by Rhodococcus spp.

Mixed bacterial cultures aerobically transformed decalin (decahydronaphthalene) dissolved in an immiscible carrier phase (heptamethylnonane; HMN) in liquid medium. Conversion was enhanced in the presence of decane, a readily degraded n-alkane, and/or HMN. Four Rhodococcus spp. isolates purified from one of the mixed cultures were active against decalin in the presence of n-decane, but their ability to use decalin as a sole carbon source for growth could not be sustained. Isolate Iso 1a oxidized decalin under co-metabolic conditions with decane vapours as the primary carbon source. Mass spectrometry and comparison to authentic standards showed that the oxidized products of decalin biotransformation were 2-decahydronaphthol and 2-decalone. Some evidence of ring-opening was obtained, but the possible ring-opened product was not definitively identified. These results are consistent with co-metabolic oxidation of decalin by enzymes active toward n-alkanes.

Mechanical properties of hexadecane-water interfaces with adsorbed hydrophobic bacteria.

This study focuses on how intact, hydrophobic bacteria in their stationary (i.e., non-dividing) phase could adsorb onto the hexadecane-water interface and alter its mechanical properties. The two strains of bacteria used in forming the interfacial films were Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c. Using the dynamic pendant drop technique, the film interfacial tension was monitored as the surface area was made to undergo transient changes. Under static conditions, both types of bacteria had no effect on the interfacial tension. When subjected to transient excitations, however, the two bacterial films exhibited clear and qualitatively similar rheological properties: they responded as two-dimensional Maxwellian materials when the interfacial areas were dilated suddenly, but appeared to be purely elastic upon rapid area compression. Such rheological behaviours are "non-linear" in that the responses of the tension to area dilation and contraction are not mirror images of one another. Despite their qualitative similarities, the two types of film had very distinct film elasticities and relaxation times. The most striking difference between the two bacterial films was revealed under continuous reduction of area, when the A. venetianus RAG-1 system displayed a "paper-like" interface, whereas the interface of the R. erythropolis 20S-E1-c system was "soap film-like". These macroscopic observations could be explained by the surface ultrastructures of the two cell strains determined using transmission electron microscopy.

Two different mechanisms for adhesion of Gram-negative bacterium, Pseudomonas fluorescens LP6a, to an oil-water interface.

Microbial adhesion to the oil-water interface is an important parameter in biodegradation of hydrocarbons to enhance uptake and metabolism of compounds with very low aqueous solubility, but the mechanisms of adhesion are not well understood. Our approach was to study a range of compounds and mechanisms to promote the adhesion of a hydrophilic bacterium, Pseudomonas fluorescens strain LP6a, to an oil-water interface. The cationic surfactants cetylpyridinium chloride (CPC), poly-l-lysine and chlorhexidine gluconate (CHX) and the long chain alcohols 1-dodecanol and farnesol increased the adhesion of P. fluorescens LP6a to n-hexadecane from ca. 30 to 90% of suspended cells adhering. In contrast, adjusting the ionic strength of the suspending medium only increased the adhesion from about 8 to 30%. The alcohols, 1-dodecanol and farnesol, also caused a dramatic change in the oil-water contact angle of the cell surface, increasing it from 24 degrees to 104 degrees , whereas the cationic compounds had little effect. In contrast, cationic compounds changed the electrophoretic mobility of the bacteria, reducing the mean zeta potential from -23 to -7 mV in 0.01 M potassium phosphate buffer, but the alcohols, 1-dodecanol and farnesol, had no effect on zeta potential. Even though both types of compounds promoted cell adhesion to the n-hexadecane interface, the mechanisms were different. Alcohols acted through altering the cell surface hydrophobicity, whereas cationic surfactants changed the surface charge density.

Sulfur from benzothiophene and alkylbenzothiophenes supports growth of Rhodococcus sp. strain JVH1.

Rhodococcus sp. strain JVH1 was previously reported to use a number of compounds with aliphatic sulfide bridges as sulfur sources for growth. We have shown that although JVH1 does not use the three-ring thiophenic sulfur compound dibenzothiophene, this strain can use the two-ring compound benzothiophene as its sole sulfur source, resulting in growth of the culture and loss of benzothiophene. Addition of inorganic sulfate to the medium reduced the conversion of benzothiophene, indicating that benzothiophene metabolism is repressed by sulfate and that benzothiophene is therefore used specifically as a sulfur source. JVH1 also used all six isomers of methylbenzothiophene and two dimethylbenzothiophene isomers as sulfur sources for growth. Metabolites identified from benzothiophene and some methylbenzothiophenes were consistent with published pathways for benzothiophene biodesulfurization. Products retaining the sulfur atom were sulfones and sultines, the sultines being formed from phenolic sulfinates under acidic extraction conditions. With 2-methylbenzothiophene, the final desulfurized product was 2-methylbenzofuran, formed by dehydration of 3-(o-hydroxyphenyl) propanone under acidic extraction conditions and indicating an oxygenative desulfination reaction. With 3-methylbenzothiophene, the final desulfurized product was 2-isopropenylphenol, indicating a hydrolytic desulfination reaction. JVH1 is the first microorganism reported to use all six isomers of methylbenzothiophene, as well as some dimethylbenzothiophene isomers, as sole sulfur sources. JVH1 therefore possesses broader sulfur extraction abilities than previously reported, including not only sulfidic compounds but also some thiophenic species.