Comparison of fatty acid content and DNA homology of the filamentous gliding bacteriaVitreoscilla,Flexibacter, Filibacter

DNA hybridization experiments showed that there was a high degree of homology amongVitreoscilla strains but not with DNA fromFilibacter limicola. Flexibacter spp were much more heterogeneous indicating a low genetic similarity. These results were also reflected in the membrane fatty acids of the bacteria. TheVitreoscilla strains were very similar with the 16:17c fatty acid being dominant. The membrane fatty acids ofF. limicola were dominated by a15:0 and a17:0 components which provided additional support for its relatedness to the genusBacillus. There was much greater diversity in the fatty acid patterns of theFlexibacter spp.F. aurantiacus, F. ruber andF. elegans shared the common dominant fatty acids 16:17c with theVitreoscilla strains, but this was replaced by the 16:16c acid inF. flexilis. F. ruber was distinguished by the absence of branched odd-chain monounsaturated fatty acids andF. elegans by the dominance of the -OH i15:0 acid. Precise determination of fatty acid double bond positions and geometry are essential for correct interpretation of increasingly complex ecological and taxonomic data sets.     

Mobilization of cloned luciferase genes into Vibrio harveyi luminescence mutants

A recombinant plasmid which carried a 5 kb fragment of Vibrio harveyi DNA containing the luxA and luxB genes was mobilized from Escherichia coli into luminescence-deficient mutants of V. harveyi. The cloned genes complemented a temperature sensitive luciferase mutation, but failed to complement lesions in two different aldehyde deficient mutants. Expression of the cloned genes was not subject to autoinduction in either E. coli or in V. harveyi.     

Chemolithotrophic growth ofDesulfovibrio desulfuricans with hydrogen coupled to ammonification of nitrate or nitrite

Two of nine sulfate reducing bacteria tested,Desulfobulbus propionicus andDesulfovibrio desulfuricans (strain Essex 6), were able to grow with nitrate as terminal electron acceptor, which was reduced to ammonia. Desulfovibrio desulfuricans was grown in chemostat culture with hydrogen plus limiting concentrations of nitrate, nitrite or sulfate as sole energy source. Growth yields up to 13.1, 8.8 or 9.7 g cell dry mass were obtained per mol nitrate, nitrite or sulfate reduced, respectively. The apparent half saturation constants (K _s) were below the detection limits of 200, 3 or 100 mol/l for nitrate, nitrite of sulfate, respectively. The maximum growth rates {ie63-1} raised from 0.124 h^-1 with sulfate and 0.150 h^-1 with nitrate to 0.193 h^-1 with nitrite as electron acceptor. Regardless of the electron acceptor in the culture medium, cell extracts exhibited absorption maxima corresponding to cytochromec and desulfoviridin. Nitrate reductase was found to be inducible by nitrate or nitrite, whereas nitrite reductase was synthesized constitutively. The activities of nitrate and nitrite reductases with hydrogen as electron donor were 0.2 and 0.3 mol/min·mg protein, respectively. If limiting amounts of hydrogen were added to culture bottles with nitrate as electron acceptor, part of the nitrate was only reduced to the level of nitrite. In media containing nitrate plus sulfate or nitrite plus sulfate, sulfate reduction was suppressed.The results demonstrate that the ammonification of nitrate or nitrite can function as sole energy conserving process in some sulfate-reducing bacteria.     

Survival of Pseudomonas fluorescens and Bacillus subtilis introduced into two soils of different texture in field microplots

Abstract Antibiotic-resistant strains of Pseudomonas fluorescens and Bacillus subtilis , produced by transposon Tn5 mutagenesis and transformation with plasmid pFT30, respectively, were characterized. Both strains grew at a rate comparable to that of the wild-type strains, and the antibiotic resistance remained stable for over 50 generations without selective pressure. During the growing season, the survival of these strains was studied in two soils of different texture cropped with wheat. The B. subtilis populations declined rapidly in both soils and then stabilized at the levels of added spores. P. fluorescens showed a slow, steady decline in both soils; survival was better in the finer-textured soil, a silt loam, than in the coarser loamy sand. For both bacteria, some translocation to deeper soil layers was observed. No significant rhizosphere effects were detected in either of the two soils.     

Some regulatory aspects of [14C]methylamine influx intoPisum sativum L. cv. Feltham First seedlings

[¹⁴C]Methylamine influx intoPisum sativum L. cv. Feltham First seedlings showed Michaelis-Menten-type kinetics with apparentV _max=49.2 mol·g^-1 FW·h^-1 and apparentK _m=0.51 mM. The competitive interactions between ammonium and methylamine were most obvious when biphasic kinetics were assumed with saturation of the first phase at 0.05 mM. The inhibitor constant for ammonium (K _i)=0.027 mM. When [¹⁴C]methylamine was used in trace amounts with ammonium added as substrate, the influx of tracer showed Michaelis-Menten-type kinetics with apparentV _max=3.46 mol·g^-1 FW·h^-1 and apparentK _m=0.15 mM. The initial rate of net ammonium uptake corresponded with that found when [¹⁴C]methylamine was used to trace ammonium influx. The latter was also stimulated by high pH_o and inhibited by nitrate. Ammonium pretreatment±methionine sulphoximine or glutamine pretreatment of the seedlings inhibited subsequent [¹⁴C]methylamine influx, while methylamine or asparagine pretreatment stimulated [¹⁴C]methylamine influx. There was also a stimulatory effect of prior inoculation withRhizobium. The results are discussed in terms of current models for the regulation of ammonium uptake in plants.     

厌氧培养皿及厌氧培养管的临床应用——对传统的厌氧菌分离培养及鉴定方法的简化

利用我们研制的厌氧培养皿及管,共检验了39份牙髓炎及牙周炎标本,分离出厌氧菌59株,标本中厌氧菌分离的阳性率为100％。其中类杆菌28株,消化链球菌9株,消化球菌7株,韦荣氏球菌5株,真杆菌2株,梭形杆菌8株。在类杆菌中产黑素类杆菌21株,占类杆菌总数的75％。结果表明使用厌氧培养皿及管研究厌氧菌简便、有效、经济,适于基层单位应用。     

Biodegradation of atrazine in surface soils and subsurface sediments collected from an agricultural research farm

The purpose of the present study was to assess atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) mineralization by indigenous microbial communities and to investigate constraints associated with atrazine biodegradation in environmental samples collected from surface soil and subsurface zones at an agricultural site in Ohio. Atrazine mineralization in soil and sediment samples was monitored as ¹⁴CO₂ evolution in biometers which were amended with ¹⁴C-labeled atrazine. Variables of interest were the position of the label ([U-¹⁴C-ring]-atrazine and [2-¹⁴C-ethyl]-atrazine), incubation temperature (25°C and 10°C), inoculation with a previously characterized atrazine-mineralizing bacterial isolate (M91-3), and the effect of sterilization prior to inoculation. In uninoculated biometers, mineralization rate constants declined with increasing sample depth. First-order mineralization rate constants were somewhat lower for [2-¹⁴C-ethyl]-atrazine when compared to those of [U-¹⁴C-ring]-atrazine. Moreover, the total amount of ¹⁴CO₂ released was less with [2-¹⁴C-ethyl]-atrazine. Mineralization at 10°C was slow and linear. In inoculated biometers, less ¹⁴CO₂ was released in [2-¹⁴C-ethyl]-atrazine experiments as compared with [U-¹⁴C-ring]-atrazine probably as a result of assimilatory incorporation of ¹⁴C into biomass. The mineralization rate constants (k) and overall extents of mineralization (P _max ) were higher in biometers that were not sterilized prior to inoculation, suggesting that the native microbial populations in the sediments were contributing to the overall release of ¹⁴CO₂ from [U-¹⁴C-ring]-atrazine and [2-¹⁴C-ethyl]-atrazine. A positive correlation between k and aqueous phase atrazine concentrations (C _eq ) in the biometers was observed at 25°C, suggesting that sorption of atrazine influenced mineralization rates. The sorption effect on atrazine mineralization was greatly diminished at 10°C. It was concluded that sorption can limit biodegradation rates of weakly-sorbing solutes at high solid-to-solution ratios and at ambient surface temperatures if an active degrading population is present. Under vadose zone and subsurface aquifer conditions, however, low temperatures and the lack of degrading organisms are likely to be primary factors limiting the biodegradation of atrazine.Abbreviations C _eq solution phase atrazine concentration at equilibrium - C _s amount of atrazine sorbed - CLA [2-¹⁴C-ethyl]-atrazine - k first-order mineralization rate constant - K _d sorption coefficient - m slope - P _max maximum amount of CO₂ released - RLA [U-¹⁴C-ring]-atrazine     

Modulation of gating of a metabolically regulated,ATP-dependent K+ channel by intracellular pH in B cells of the pancreatic islet

Summary Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated. ATP-sensitive K⁺ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pH _i . (1) The time course of K⁺(ATP) channel activity during exposure to and washout of NH₄Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH₄Cl entry and inhibition of the Na _o ⁺ H _i ⁺ exchanger, resembles the time course of pH _i measured in other cell types that have been similarly treated. (2) Increasing pH _o over the range 6.25–7.9 increases K⁺(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H⁺ by the application of the K⁺/H⁺ exchanger nigericin. (3) Increasing pH _i over a similar range produces similar effects on K⁺(ATP) channels in inside-out excised patches exposed to small concentrations of ATP _i . The physiological role of pH _i in the metabolic gating of this channel remains to be explored.     

Reduction of tetrazolium salts by sulfate-reducing bacteria

Abstract The reduction of tetrazolium salts by the sulfate-reducing bacteria, Desulfovibrio desulfuricans and Desulfotomaculum orientis , was examined. D. desulfuricans and D. orientis reduced triphenyltetrazolium chloride (TTC) and 2-( p -iodophenyl)-3-( p -nitrophenyl)-5-phenyltetrazolium chloride (INT) forming intracellular formazan deposits. The reduction rate of INT was higher than that of TTC. INT reduction was not inhibited by the addition of sulfate or molybdate, and sulfate uptake was inhibited by the addition of both INT and molybdate. The ratio of intracellular formazan forming cells to acridine orange direct counts in both strains decreased with culture age and starvation time.     

Enumeration of anaerobic oxalate-degrading bacteria in the ruminal contents of sheep

Abstract Concentrations of oxalate-degrading anaerobes in ruminal contents of sheep were determined from counts of colonies producing clear zones on a calcium oxalate medium (D agar with 7 mM CaCl₂). Viable counts of oxalate degraders from a 55-kg sheep fed a diet containing 32% halogeton (4.6% oxalate) averaged 2.6 × 10⁶/ g (dry weight). When the halogeton concentration in the diet was reduced to 16%, counts of oxalate degraders decreased nearly 300-fold. Oxalate-degrading isolates from this sheep were similar to OxB, the type strain of Oxalobacter formigenes . When a 45-kg sheep was fed diets containing 2.2, 1.5, and 0.8% oxalate, viable counts of oxalate degraders (enumerated on D agar with 14 mM CaCl₂ and 20% filter-sterilized ruminal fluid) represented 0.85, 0.52, and 0.06% of the total viable population, respectively; total viable counts were essentially unchanges by these concentrations of dietary oxalate. Similar percentages of oxalate degraders were also observed when a 23-kg sheep was fed diets containing 1.5 or 0.8% oxalate. This report presents the first direct measurements of the concentrations of oxalate-degrading bacteria in the rumen and supports the concept that the availability of oxalate in the diet influences the proportion of oxalate-degrading bacteria in the rumen