Wk Incubation Research Articles

Property Characterization of Peanut Kernels Subjected to Gamma Irradiation and Its Effect on the Outgrowth and Aflatoxin Production by Aspergillus parasiticus

ABSTRACTPeanut kernels inoculated with Aspergillus parasiticus conidia and uninoculated kernels were gamma irradiated with 0 to 15 kGy using 60Co. Levels of 2.5 and 5.0 KGy were effective in retarding the outgrowth of A. parasiticus and reducing the population of natural mold contaminants. However, elimination of these molds was not achieved. When irradiated with doses higher than 10 KGy, seed germinations were inhibited, changes in proteins were observed and oil stabilities decreased. After 4 wk incubation of the inoculated kernels in a humidified condition, aflatoxins produced by surviving A. parasiticus ranged from 69.12 to 13.48 μg/g depending upon the original irradiation dose.

Effect of Rhizopus and Neurospora spp. on growth of Aspergillus flavus and A. parasiticus and accumulation of aflatoxin B 1 in groundnut

The influence of Rhizopus and Neurospora spp. on growth and aflatoxin B1 accumulation of Aspergillus flavus and A. parasiticus was investigated. When inoculated simultaneously with Rhizopus or Neurospora spp. on mashed groundnuts, Aspergillus spp. were able to grow, but to a lesser extent and with visually different mycelial development and sporulation behaviour. Accumulation of aflatoxin B1 observed during a 6 wk incubation, averaged 34% in mixed cultures with Rhizopus spp. and 1–7% in mixtures with Neurospora spp., as compared to pure cultures of Aspergillus spp. On aqueous groundnut extract selected strains of Rhizopus and Neurospora showed the ability to cause an exhaustion particularly of C compounds, inhibiting Aspergillus growth and aflatoxin BL accumulation. There was also evidence for the formation of Rhizopus and Neurospora metabolites inhibiting growth and/or aflatoxin B1 production. In addition Rhizopus and Neurospora strains degraded aflatoxin B1.

Response of epiphytic diatom communities from the tailwaters of glen Canyon Dam, Arizona, to elevated water temperature

AbstractThe composition of epiphytic diatom communities from the cold tailwaters (12°C) of Glen Canyon Dam, Arizona, was analysed after a 2 wk incubation period at 12°C, 18°C and 21°C. There was a significant change in diatom composition between 12°C and 18°C, while no significant changes occurred between 18°C and 21°C. This suggests that a temperature threshold exists between 12°C and 18°C for the diatom flora in the tailwaters of Glen Canyon Dam. At the two higher water temperatures, smaller and closely adnate taxa became more important numerically than larger, upright, cold water stenotherms. The potential importance of this compositional shift in epiphytic diatoms on macroinvertebrate grazers has management implications regarding different release programs from reservoirs.

Accumulation of tetrodotoxin in marine sediment

Tetrodotoxin (TTX) was accumulated at high concentrations in sediment samples from 2 inner water stations and 1 deep-sea station in the western Pacific off the coast of Japan. TTX was identified using tissue culture bioassay and HPLC. It is suggested that bacteria inhabiting the sediment are responsible for the production of toxin. The widespread occurrence of TTX in marine sediments is predicted; such large concentrations of TTX may affect animals inhabiting these sediments. Tetrodotoxin (TTX), known as 'puffer fish toxin', is a potent neurotoxin which blocks the sodium channel of neuronal cells. It has recently been established that this toxin is present in diverse groups of animals, especially those of marine environments (Mosher & Fuhrman 1984, Thuesen et al. 1988). Although mechanisms of TTX accumulation are still obscure, the widespread occurrence of marine bacteria which produce tetrodotoxin (Simidu et al. 1987) suggests that bacteria are responsible for the production of TTX in natural environments. Since marine sediments generally contain large bacterial populations, we investigated the presence of TTX or related sodium channel blocking agents in these sediments and consider the possible accumulation of TTX in the environment. Sediment samples, including one from 4033 m depth, were analyzed by a newly developed tissue culture assay method (Kogure et al. 1988) and by high performance liquid chromatography (HPLC). Sediment samples were taken using a Phleger corer from 2 stations in Tokyo Bay (Stns A and B), which is highly polluted, and 1 station in an open ocean deep area (Stn C), during the KT-87-17 cruise of the RV 'Tansei Maru', Ocean Research Institute, University of Tokyo, in November 1987 (Fig. 1). Sediment samples were separated into layers on board immediately after collection. A portion of them were used to enumerate heterotrophic bacteria, while the rest were kept at -20 C until toxin extraction in the laboratory. Bacterial colonies appearing on ZoBell's 2216E agar plates were counted after 3 wk incubation at 20°C. For the extraction of toxins, sediment samples were thawed, mixed with 10 times their volume of 0.1 % acetic acid, and boiled for 20 min. After centrifugation a t 25 000 X g, the supernatant was freeze-dried and reconstituted in a small amount of distilled water. Samples for HPLC analysis were further purified using SEP-PAK CI8 cartridges (Waters Associates). Tissue culture bioassay (Kogure et al. 1988) was used for the detection and quantitative measurement of sodium channel blocking toxin in the samples. In brief, the alkaloid toxin veratridine causes sodium influx in the mouse neuroblastoma cell line Neuro 2A (ATCC, CCL 131), when the function of Naf-K+ATPase is inhi1 . , ol~eci by uudbdi~ l . This causes celiuiar sweiling and subsequent death; TTX and similar sodium channel blocking agents counteract this effect and enable cells to continue growing. The ratio of living to dead cells can be used to estimate the concentration of toxin in

COMPARAISON DE DIFFÉRENTES MÉTHODES D'ANALYSE DE L'AZOTE DU SOL EN RELATION AVEC SA DISPONIBILITÉ POUR LES PLANTES

The objective of this study was to compare several methods of estimating the availability of soil nitrogen to plants. Total soil N, organic matter content, mineralized N during a 2 wk incubation at 35 °C, organic N in 6 N HC1, 0.01 M NaHCO3 and 1 N KCl extracts, and finally mineral N extracted by 2 N KCl were evaluated and contrasted with N uptake by sugar beets cultivated on 19 soils in a greenhouse experiment. The relative yield or plant N uptake gave the highest correlation coefficients when both mineral and organic N fractions in soil extract were considered. The incubation methods gave the best correlation coefficient with relative yield (R2 = 0.85**). N contents in NaHCO3 extract were more correlated with relative yield or N uptake than total N, organic matter contents or N extracted by 6 N HCl or 1 N KCl. The UV absorbance values obtained at 205 nm with 0.01 M NaHCO3 extract were also well correlated with relative yield (R2 = 0.78**) and plant N uptake (R2 = 0.66**). At this wavelength, as well as at 220 nm, the absorbance was affected by mineral and organic N contents in the extract. However, at 260 nm, the UV absorbance was only related to organic N in the extract; consequently these absorbance values were less correlated with relative yield (R2 = 0.49**) or N uptake (R2 = 0.27*). Furthermore, the absorbance measured at 205 nm was too sensitive to NO3-N and organic N concentration and this relationship was not linear in the high-N concentration range. The UV absorbance at 220 nm in the 0.01M NaHCO3 extract seemed to be a promising method to evaluate the availability of soil N. Key words: Soil nitrogen, incubation, ultraviolet absorbance, hydrolyzable nitrogen

Bacterial, fungal and protozoan responses to chloroform fumigation in stored soil

Microbial biomass estimated by CO 2 evolution following fumigation was 2.5–14.7 times greater than that estimated by direct microscopy in prairie soil. Bacteria, fungi and protozoa were counted by direct microscopy before, during and periodically for 10 days following chloroform fumigation and compared with microbial biomass as estimated by CO 2 evolution and N mineralization following chloroform fumigation. Protozoan populations were reduced to below detection levels immediately after fumigation and remained below detection levels during incubation following fumigation. Bacterial and fungal populations were reduced by fumigation to 37–79% of their original populations but usually recovered to their initial numbers by the second day following fumigation. In one case protozoa contributed up to 74 μg C, or about half of the total microbial biomass, to CO 2 evolution following fumigation. Microbial biomass was estimated in soil wetted to 60% of water-holding capacity (WHC) 1 wk or 1 day before fumigation. Microbial activity changed during the 1 wk incubation before fumigation but not total microbial biomass determined by microscopy. The ratio of CO 2 evolved-to-N mineralized followed fumigation changed in direct proportion to the ratio of fungal-to-bacterial biomass present in the soil before fumigation. Although more experiments with different soils should be performed, these results indicate that CO 2 evolved or N mineralized varies with the ratio of fungal-to-bacterial biomass initially present.

Inhibition of Clostridium botulinurn Type E in Model Acidified Food Systems

ABSTRACTThe potential for growth and toxigenesis of a mixture of three strains of C. botulinum type E in model food systems at pH levels of 4.600 and 4.200 was investigated. Whole shrimp, shrimp puree, tomato puree, and tomato and shrimp puree were acidified to pH levels of 4.200 and 4.600 with acetic or citric acid. Inoculated and uninoculated control samples were tested during 8 wk incubation at 26°C. No significant C. botulinum growth or toxigenesis was detected in the food systems over the 8 wk test period and the pH of the various foods remained generally constant. This investigation affirms the safety of the generally accepted inhibitory pH level of 4.6 in the food systems studied.

Promotion of bone dissolution by excessive fluoride in acidic buffer solution

In order to quantitatively examine fluoride uptake by bone and the effect on its chemical and physical properties, rat bone was incubated in acidic buffer solutions (pH 5) with fluoride concentrations of 0–1000 ppm F. After 1 wk incubation, there was a substantial increase in the crystallinity of the bone mineral with increasing fluoride concentration in the solution. The calcium concentration in the solutions used for incubation decreased dramatically, with increased levels of fluoride in the solution, approaching a plateau. The phosphate concentration initially decreased, with increasing levels of fluoride in proportion to the decrease of calcium concentration, and then increased when the fluoride concentration of the solution was above 200–300 ppm. These phenomena, when considered with X-ray diffraction data, reflected the formation of CaF 2. The increase of the phosphate concentration in the solution suggests that the presence of excessive fluoride in the acidic buffer solution may promote the dissolution of soluble bone apatites, in spite of the dissolution-preventive activity of fluoride.

Coprinus Verticillatus, a New Agaric with Multiple Clamps

Click to increase image sizeClick to decrease image sizeKey Words: Coprinus verticillatuscoprophilous fungidesert fungi

Diversity of human granulopoietic precursor cells: separation of cells that form colonies in diffusion chambers (CFU-d) from populations of colony-forming cells in vitro (CFU-c) by velocity sedimentation

Normal human bone marrow contains cells that form granulocytic colonies in fibrin clot diffusion chambers implanted intraperitoneally in sublethally irradiated mice (CFU-d). A series of experiments was performed to determine the relationship between CFU-d and the cells that form colonies in agar culture in vitro (CFU-c). Low-density bone marrow cells ( 3 ) were separated by velocity sedimentation and colony-forming cells in each fraction assessed by culture in diffusion chambers and in soft agar. CFU-d sedimented more slowly than the vast majority of CFU-c, with a peak sedimentation velocity of 5.0 ± 0.4 mm/hr. Two different CFU-c populations could be distinguished. One was a rapidly sedimenting cell population (7.3 ± 0.9 mm/hr.) that formed colonies after 1 wk incubation in vitro. On day 14, however, colonies were derived from more slowly sedimenting cells that had a peak sedimentation velocity of 6.0 ± 0.5 mm/hr. Clusters (3-50 cells), scored on day 7 in agar ##

Effects of Temperature and Photoperiod on the Egg Diapause of Labops hesperius Uhler 1 , 2

Labops hesperius Uhler diapauses as an egg that is in an advanced stage of embryogenesis with well-developed head, eyes, and appendages. Eggs required a minimum of 60 days chilling at 3 or 9°C and approximately 2 wk incubation at 15°C to hatch. Exposure to –15°C did not prevent hatching and, in general, the percent hatch was greater when the eggs were gradually acclimated to 3 or –15°C. Eggs did not hatch if the chilling began in August but 40% or more of the eggs hatched when exposure to cold was delayed until September, October, or November. Length and sequence of different photoperiods in both the chill and incubation temperatures also significantly influenced the percent hatch.

Practical Aspects of Survival and Destruction of Infectious Pancreatic Necrosis Virus

The survival of infectious pancreatic necrosis (IPN) virus under conditions of practical import and its susceptibility to destruction by two common disinfecting agents were examined. An indigenous strain of virus, shed to trough water at a concentration of 105 TCID50 per milliliter during an epizootic, lost 99% of its infectivity in fresh water at 4 C in 10–12 wk. There was residual infectivity after 24 wk. Survival was prolonged in sea water where loss of activity of an ATCC strain after 10 wk incubation at either 4 or 10 C was negligible. The loss in 5–6 mo was under 99%.IPN virus (107 TCID50/ml) survived drying in air at laboratory temperature and humidity for 5 but not for 6 wk. Under reduced humidity, residual infectivity was still evident after 8 wk.At a titer of 105.0 TCID50/ml, IPN virus was completely inactivated by exposure to 25 ppm available chlorine in 30 min. A concentration of 40 ppm available chlorine was required to inactivate 107.5 TCID50 of virus/ml in the same period of time. IPN virus, at a titer of 105.5 TCID50/ml, was totally destroyed by 30 ppm active iodine (Wescodyne) in 5 min. An increase in virus concentration, to 106.6 TCID50/ml increased the iodine requirement to 35 ppm to achieve the same result.The implications for salmonid culture of the persistence of IPN virus in an aqueous environment and its resistance to destructive agents are discussed.

EFFECTS OF NITROGEN CONCENTRATION ON THE TRANSFORMATION OF BAND-APPLIED NITROGEN FERTILIZERS

The concentration of the ammonium form of N (NH4+ + NH3) at the fertilizer zone in a neutral Wellwood soil (pH 6.6) banded with (NH2)2CO and NH4OH had an effect on nitrite accumulation. Nitrite accumulated when (NH2)2CO and NH4OH were banded at rates of 800 and 200 kg N/ha (on an area basis), but no nitrite accumulated at 100 kg N/ha. With urea, the lowest rate at which nitrite accumulated (200 kg N/ha) corresponded to an ammonium concentration near the fertilizer band of 750 ppm after 1 wk incubation, and 400 ppm N after 2 wk incubation. At a rate of 100 kg N/ha where no nitrite accumulated, the concentration of ammonium form was 500 ppm N and 250 ppm N at 1 and 2 wk, respectively. Irrespective of the rate of N, only a trace of nitrite accumulated when soil was banded with (NH4)2SO4 and incubated.