丙烯酸对十六碳二元酸发酵的影响和16L罐扩试

本文报道丙烯酸对发酵生产十六碳二元酸(DC_(16))的影响,加入0.1%丙烯酸,DC_(16)产量提高20—30%.在16L自动控制罐上,在最佳条件下,加入20%(v/v)正十六烷(nC_(16)),发酵5天,DC_(16)高达120g/L,nC_(16)的转化率高达79%.     

The Effects of a Bacillus Biosurfactant on Methanogenic Hexadecane Degradation

The effects of microbially produced biosurfactants on hydrocarbon degradation have been examined previously by other researchers. However, almost all of these studies were conducted using rhamnolipid biosurfactants produced by various Pseudomonas species under aerobic conditions. The purpose of this study was to elucidate the effects of various levels of the Bacillus sp. JF2 lipopeptide biosurfactant on the degradation of hexadecane under methanogenic conditions. Hexadecane degradation did increase significantly when levels below critical micelle concentration of the pre-purified biosurfactant were added. However, at levels above this amount of biosurfactant, degradation of hexadecane appeared to be inhibited. The terminal electron accepting process, methanogenesis, was stimulated by surfactant addition. A review of the published literature revealed a wide variety of results, some which are similar to, but many that differ from those reported here. However, the results from this study were reproducible. Although there is no clear explanation for these results, more research on the effect of biosurfactants produced by Gram positive bacteria on the biodegradation of hydrocarbons is needed, as well as further studies under anaerobic conditions.     

Cryptococcus haglerorum,sp. nov., an anamorphic basidiomycetous yeast isolated from nests of the leaf-cutting ant Atta sexdens

A yeast strain (CBS 8902) was isolated from the nest of a leaf-cutting ant and was shown to be related to Cryptococcus humicola. Sequencing of the D1/D2 region of the 26S ribosomal DNA and physiological characterization revealed a separate taxonomic position. A novel species named Cryptococcus haglerorum is proposed to accommodate strain CBS 8902 that assimilates n-hexadecane and several benzene compounds. Physiological characteristics distinguishing the novel species from some other members of the C. humicola complex are presented. The phylogenetic relationship of these strains to species of the genus Trichosporon Behrend is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hydrophobic cell surface and bioflocculation behavior of Rhodococcus erythropolis

An alkane-biodegrading bacterium identified as Rhodococcus erythropolis (NTU-1 strain) was isolated from petroleum contaminated soil. The major purpose of the current research was to study the issues regarding biofloccules formation and cell surface hydrophobicity of NTU-1. When long-chain alkanes are supplied as the carbon source, NTU-1 tends to form biofloccules and remove significant amount of alkanes by biodegradation and physical trapping. Approximately, more than 95% of each alkane could be efficiently removed within 40–68 h. The bioremediation process was accompanied by formation of biofloccules with size ranging from 0.1 to 2 cm in diameter. The MATH test and the hydrophobic slide experiment suggested that NTU-1 might possess a hydrophobic cell surface which is one of the important factors in the formation of biofloccules. It provides the interaction of cells with hydrocarbon droplets effectively and further aggregate into larger clumps. Besides, when grown on n-hexadecane, experimental results revealed that there were at least 11 different growth-associated fatty acids produced, with carbon chain length ranging from 12 to 24, and cell surface hydrophobicity was enhanced via accumulation at the cell surface.     

Sophorolipid production from different lipid precursors observed with LC-MS

An HPLC-MSⁿ system was used to quantify and identify the structures of individual sophorolipid components produced in Torulopsis bombicola fermentation on glucose with or without hexadecane or soybean oil. With glucose alone, the SL production was minimal and the products were complex mixtures with mainly acidic SLs. The SLs produced with glucose plus soybean oil were also complex, containing both lactonic and acidic SLs with saturated and unsaturated C16 and C18 fatty acid moieties. The glucose plus hexadecane system gave the highest production rate and product selectivity, forming primarily two diacetylated lactonic isomers with palmitate as the fatty acid moiety. A close structure correspondence between the SL’s lipid moiety and the lipid precursor used was observed. The change of the composition of SL mixtures along batch fermentation was further examined. The concentrations of acidic SLs increased very gradually throughout the process. The production of lactonic SLs became appreciable following the addition of hexadecane or soybean oil at 24 h, and increased much more rapidly after the culture reached the stationary phase. The combined percentage of the main lactonic SLs leveled off at 80% for the hexadecane system and 50% for the soybean oil system. The yields of crude SLs were 0.84, 0.20, and 0.03 g per gram of hexadecane, soybean oil, and glucose consumed during the SL production phase. Hexadecane is thus a more efficient second C-source for sophorolipid production.     

Characterization of bacterial isolates from industrial wastewater according to probable modes of hexadecane uptake

Bacterial isolates from industrial wastewater were characterized according to probable modes of hexadecane uptake based on data for cell surface hydrophobicity, emulsifying activity, glycoside content and surface tension of cell-free culture medium. The results obtained suggested that both modes of biosurfactant-enhanced hexadecane uptake by bacterial strains take place, direct uptake and alkane transfer. The increase in cell surface hydrophobicity and glycoside production by the strains suggested the existence of biosurfactant-enhanced interfacial uptake of the alkane. Such mechanism is probably predominant for three isolates, Staphylococcus sp. HW-2, Streptococcus sp. HW-9 and Bacillus sp. HW-4. Secreted biosurfactants enhanced mainly alkane emulsification for most hydrophobic isolate Arthrobacter sp. HW-8, and micellar transfer for most hydrophilic isolate Streptococcus sp. HW-5. For other strains (67%) both mechanisms of biosurfactant-enhanced hexadecane uptake probably take place in similar degree, interfacial uptake and alkane emulsification. The results obtained could contribute to clarifying the natural relationships between the members of water ecosystem studied as well as will reveal potential producers of surface active compounds.     

Measurement of the kinetics of bacterial adherence to hexadecane in polystyrene cuvettes

Abstract The kinetics of bacterial adherence to hexadecane were measured using disposable polystyrene cuvettes. The rate of adherence was exponential, and was itself linearly dependent on the water:hexadecane ratio employed. The dependency of the rate of adherence on the water:hexadecane ratio, termed the removal coefficient, varied from 4.7 min⁻¹ for Streptococcus pyogenes to 72 min⁻¹ for Acinetobacter calcoaceticus . The removal coefficient of Serratia marcescens was a function of growth temperature, 48 min⁻¹ following growth at 30°C as opposed to 5.8 min⁻¹ for 35°C-grown cells.     

Anaerobic oxidation of saturated hydrocarbons to CO2 by a new type of sulfate-reducing bacterium

n-Hexadecane added as electron donor and carbon source to an anaerobic enrichment culture from an oil production plant or to anoxic marine sediment samples allowed dissimilatory sulfate reduction to sulfide. The enrichment from the oil field was purified via serial dilutions in liquid medium under a hexadecane phase and in agar medium with caprylate. A pure culture of a sulfate-reducing bacterium, strain Hxd3, with relatively tiny cells (0.4–0.5 by 0.8–2 m) was isolated that grew anaerobically on hexadecane without addition of further organic substrates. Most of the cells were found to adhere to the hydrocarbon phase. It was verified that neither organic impurities in hexadecane nor residual oxygen were responsible for growth. Strain Hxd3 was grown with n-hexadecane of high purity (99.5%) in anoxic glass ampoules sealed by fusion. Of 0.4 ml hexadecane added per l (1.4 mmol per l), 90% was degraded with concomitant reduction of sulfate. Controls with pasteurized cells or a common Desulfovibrio species neither consumed hexadecane nor reduced sulfate. Incubation of cell-free medium with low reducing capacity and a redox indicator showed that the ampoules were completely oxygen-tight. Measured degradation balances and enzyme activities suggested a complete oxidation of the alkane to CO₂ via the carbon monoxide dehydrogenase pathway. However, the first step in anaerobic alkane oxidation is unknown. On hexadecane, strain Hxd3 produced as much as 15 to 20 mM H₂S, but growth was rather slow; with 5% inoculum, cultures were fully grown after 5 to 7 weeks. The new sulfate reducer grew on alkanes from C₁₂ to C₂₀, 1-hexadecene, 1-hexadecanol, 2-hexadecanol, palmitate and stearate. Best growth occurred on stearate (doubling time around 26 h). Growth on soluble fatty acids such as caprylate was very poor. Alkanes with chains shorter than C₁₂, lactate, ethanol or H₂ were not used. Strain Hxd3 is the first anaerobe shown to grow definitely on saturated hydrocarbons.Abbreviations CO dehydrogenase carbon monoxide dehydrogenase - DTE 1,4-dithioerythritol - Tris tris(hydroxymethyl)-aminomethane Dedicated to Dr. Ralph S. Wolfe on occasion of his 70th birthday     

染色体DNA转化原生质球构建解烃工程菌

用供体菌C_(20-11)和D_(36-3)染色体DNA转化受体菌T_3原生质球。采用5mg/ml溶菌酶,37℃水浴1小时制备原生质球。原生质球形成率为99％,再生率为72.5％。在30％、PEG6000和0.1MCaC1_2作用下,供体DNA转化受体原生质球。我们用上述条件构建了能够同时降解以下四种碳源:苯甲酸、萘、樟脑、十六烷的工程菌株TCD32-14-1。     

DNA from Serratia marcescens confers a hydrophobic character in Escherichia coli

Abstract In order to determine whether hydrophobic surface properties of Serratia marcescens can be transferred to Escherichia coli , E. coli DH5α cells were transformed by DNA fragments from S. marcescens RZ. Fifteen-hundred E. coli transformants were screened for adhesion to hexadecane and polystyrene. One transformant exhibited increased adhesion to hexadecane droplets, as well as altered kinetics of aggregation in the presence of ammonium sulfate. Western colony blotting revealed that antibodies raised against S. marcescens RZ recognized components) on the transformant outer surface.