Effect of corn and peanut cultivation on soil populations of Aspergillus flavus and A. parasiticus in southwestern Georgia.

The effect of corn and peanut cultivation on the proportion of Aspergillus flavus to A. parasiticus in soil was examined. Soil populations were monitored in three fields during three different years in southwestern Georgia. Each field was planted in both peanuts and corn, and soil was sampled within plots for each crop. A. flavus and A. parasiticus were present in similar proportions in plots from all fields at the beginning of the growing season. A. terreus, A. niger, and A. fumigatus were the other dominant aspergilli in soil. Fields A and B did not show drought stress in peanut or corn plants, and soil populations of A. flavus and A. parasiticus remained stable during the course of the year. In field C, drought stress in corn plants with associated A. flavus infection and aflatoxin contamination greatly increased soil populations of A. flavus relative to A. parasiticus upon dispersal of corn debris to the soil surface by a combine harvester. Colonization of organic debris after it has been added to the soil may maintain soil populations of A. parasiticus despite lower crop infection.     

The cytidylyltransferase superfamily: Identification of the nucleotide-binding site and fold prediction

The crystal structure of glycerol-3-phosphate cytidylyltransferase from B. subtilis (TagD) is about to be solved. Here, we report a testable structure prediction based on the identification by sequence analysis of a superfamily of functionally diverse but structurally similar nucleotide-binding enzymes. We predict that TagD is a member of this family. The most conserved region in this superfamily resembles the ATP-binding HiGH motif of class I aminoacyI-tRNA synthetases. The predicted secondary structure of cytidylyltransferase and its homologues is compatible with the α/β topography of the class I aminoacyl-tRNA synthetases. The hypothesis of similarity of fold is strengthened by sequence-structure alignment and 3D model building using the known structure of tyrosyl tRNA synthetase as template. The proposed 3D model of TagD is plausible both structurally, with a well packed hydrophobic core, and functionally, as the most conserved residues cluster around the putative nucleotide binding site. If correct, the model would imply a very ancient evolutionary link between class I tRNA synthetases and the novel cytidylyltransferase superfamily. © 1995 Wiley-Liss, Inc.     

Occurrence of α-acetolactate decarboxylases among lactic acid bacteria and their utilization for maturation of beer

Summary Acetolactate decarboxylase activity has been detected among three genera, nine species and 263 strains of lactic acid bacteria tested in the course of a screening for acetolactate decarboxylases amenable for use in brewing as maturation aid. Streptococcus diacetylactis strain FD-64-D was found to generate a decarboxylase exhibiting a satisfactory activity and an excellent stability at the pH prevailing in beer and wort. This decarboxylase could not be solubilized but enzymatically active, freeze-dried cells were effective for satisfactory flavour maturation of beer although difficulties were encountered during attempts to remove the applied cell material by filtration of the beer. Lactobacillus casei DSM 2547 was likewise found to produce a decarboxylase exhibiting a satisfactory activity and stability at the low pH of beer and which, in addition, was readily solubilized. A method has been developed for pilot scale production of preparations of this decarboxylase suitable for use in brewing.Abbreviations DSM Deutsche Sammlung von Microorganismen - EDTA Ethylene diaminetetra-acetic acid     

Statistical analysis of single sodium channels. Effects of N-bromoacetamide

Currents were obtained from single sodium channels in outside-out excised patches of membrane from the cell line GH3. The currents were examined in control patches and in patches treated with N- bromoacetamide ( NBA ) to remove inactivation. The single-channel current-voltage relationship was linear over the range -60 to + 10 mV, and was unaffected by NBA . The slope conductance at 9.3 degrees C was 12 pS, and the Q10 for single channel currents was about 1.35. The currents in both control and NBA -treated patches showed evidence of a slow process similar to desensitization in acetylcholine-receptor channels. This process was especially apparent at rapid rates of stimulation (5 Hz), where openings occurred in clusters of records. The clustering of records with and without openings was analyzed by runs analysis, which showed a statistically significant trend toward nonrandom ordering in the responses of channels to voltage pulses. NBA made this nonrandom pattern more apparent. The probability that an individual channel was "hibernating" during an activating depolarization was estimated by a maximum likelihood method. The lifetime of the open state was also estimated by a maximum likelihood method, and was examined as a function of voltage. In control patches the open time was mildly voltage-dependent, showing a maximum at about -50 mV. In NBA -treated patches the open time was greater than in the control case and increased monotonically with depolarization; it asymptotically approached that of the control patches at hyperpolarized potentials. By comparing channel open times in control and NBA -treated patches, we determined beta A and beta I, the rate constants for closing activation gates and fast inactivation gates. Beta I was an exponential function of voltage, increasing e-fold for 34 mV. beta A had the opposite voltage dependence. The probability of an open channel closing its fast inactivation gate, rather than its activation gate, increased linearly with depolarization from -60 to -10 mV. These results indicate that inactivation is inherently voltage dependent.     

Equilibrium and metastable states in lecithin films.

We have considered whether lecithin surface films below the gel-liquid crystal transition temperature, Tc, are in unique physical states. In general, below Tc, equilibrium films do not exist when surface pressures, pi, exceed about 0.1 dyn/cm. Since surface pressure-surface area isotherms of lecithin films below Tc always encompass pi's much greater than 0.1 dyn/cm, the film states are metastable. We show that the film properties under these conditions depend strongly on the history of the film, particularly the method of film formation. Lecithin surface films below Tc are thus in arbitrary metastable states, so that pi-area isotherms are difficult to interpret. The physical significance of such isotherms remains to be determined. The utility of pure lecithin surface layers below Tc as models for biological systems is also challenged by our results.     

A [Na+]o-independent, pHo-dependent mechanism for reduction of intracellular [Ca2+] after influx through Ca2+ channels in mouse pituitary cells

The effect of extracellular pH (pHo) on the duration of calcium-dependent chloride currents (ICl(Ca] was studied in voltage clamped AtT-20 pituitary cells. ICl(Ca) was activated by Ca2+ influx through plasma membrane Ca2+ channels, which were opened by step depolarization to voltages between -20 and +60 mV. Increasing pHo from 7.3 to 8.0 reversibly prolonged ICl(Ca) tail currents in perforated patch recordings from cells bathed in both Na(+)-containing and Na(+)-free solutions. This prolongation was prevented in standard whole cell recordings when the pipette solution contained 0.5 mM EGTA. The effects of raised pHo were not due to alteration of intracellular pH, since tail current prolongation still occurred when intracellular pH was buffered at 7.3 with 80 mM HEPES. The prolongation of ICl(Ca) at pHo 8 could not be accounted for by a direct action on Ca2+ channels, since tail currents were prolonged when pHo was changed rapidly during the tail current, after all Ca2+ channels were closed. The effects of increasing pHo on ICl(Ca) also could not be explained by a direct action on Cl- channels, since changing to pHo 8 did not prolong Cl- tail currents when intracellular Ca2+ concentration [( Ca2+]i) was fixed by EGTA in whole cell recordings. Raising pHo did, however, prolong depolarization-evoked [Ca2+]i transients, measured directly with the Ca2+ indicator dye, fura-2. Taken together, these data demonstrate the presence of a Na(+)-independent, pHo-sensitive mechanism for reduction of [Ca2+]i after influx through Ca2+ channels. This mechanism is associated with the plasma membrane, and is active on a time scale that is relevant to the duration of single action potentials in these cells. We suggest that this mechanism is the plasma membrane Ca2+ ATPase.     

The influence of biomass and structure of the crustacean plankton on the water transparency in the Saidenbach storage reservoir

Planktonic crustacean biomass as well as structure are important factors influencing water transparency. The significant dependence of the water quality (Secchi depth) on the concentration and the share of the Daphnia biovolume and not on the total Crustacea biovolume in the Saidenbach reservoir indicates that the density of the Crustacea is only a measure of the cleaning performance, if Daphnia dominates. Using the mean size, the influence of the crustacean structure on the Secchi depth can be recorded. If big size categories prevail (like Daphnia) the water transparency is high. The mainly occurrence of little species (Mesocyclops, Bosmina) results in lower Secchi depths. However, a well defined (significant) relationship is being prevented by the different feeding behaviour of the several species.     

Biochemical and physiological characterization of the efrotomycin fermentation

Summary An efrotomycin fermentation was characterized through physical, chemical and biochemical studies. Growth of the actinomycete,Nocardia lactamdurans occurred during the first 50 h of the fermentation cycle at the expense of glucose, protein, and triglycerides. The initiation of efrotomycin biosynthesis was observed when glucose dropped to a low concentration. Upon glucose depletion, cell growth ceased and a switch in the respiratory quotient occurred. Efrotomycin biosynthesis was supported by the utilization of soybean oil and starch. Analysis of triglyceride metabolism showed that no diglycerides or monoglycerides accumulated during the fermentation. The activity of extracellular enzymes (lipase, protease, and amylase) increase during the cell growth phase and decreased significantly after 150 h. The concentrations of DNA, tetrahydro-vitamin K₂ (a membrane component), and free amino acids in the supernatant increased dramatically late in the fermentation cycle (225 h), indicating massive cell lysis. During this same time period, a reduction in cellular respiratory activity and efrotomycin biosynthesis were observed.