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Biomedical subjects

J W Bennett

Publications and source records attributed to J W Bennett.

At least 55 records · Page 3Linked to original sources
PubMed1982

Growth of high aflatoxin B2 mutants on defined and complex media and with ethoxyquin.

The major naturally occurring aflatoxins are B1, B2, G1, and G2. A precursor-product relationship between B1 and the other toxins has been assumed by many workers, but experimental data are conflicting. Four independent reports, of mutants which produce aflatoxin B2, provide genetic evidence supporting an alternate origin for B2. Five high aflatoxin B2 mutants were obtained and grown in defined and complex liquid media and on a solid complex medium in order to determine the stability of the high B2 phenotype on different substrates and to define optimal levels of production. All the high B2 strains tested produced some aflatoxin yields were quite variable. The highest production was on complex liquid medium containing yeast extract. It was not possible to confirm reports that the antioxidant ethoxyquin was an inhibitor of G aflatoxins.

Aflatoxins↗
PubMed1981

Influence of white light on production of aflatoxins and anthraquinones in Aspergillus parasiticus.

The effect of continuous light and continuous darkness on the growth of Aspergillus parasiticus and on the production of aflatoxin, averufin, versicolorin A, and versicolorin C by Aspergillus parasiticus were determined at six different temperatures with six replicates for each experiment. No growth was observed at 15 degrees C in the light, although slight growth was observed at this temperature in the dark. No aflatoxins or anthraquinones were produced in the light or dark at 35 and 40 degrees C, although growth was good at these temperatures. Differences in aflatoxins and anthraquinones for cultures grown in light and in dark were consistent at each temperature. Higher mean quantities of these secondary metabolites were produced in the light at 20 and 25 degrees C; lower mean quantities were produced in the light at 30 degrees C. The ranges of values overlapped considerably, but in all cases the differences between temperatures were significant.

Aflatoxins↗
PubMed1980

Identification of averantin as an aflatoxin B1 precursor: placement in the biosynthetic pathway.

A new blocked mutant of Aspergillus parasiticus produces no detectable aflatoxin B1, but accumulates several polyhydroxyanthraquinones. One of these pigments was identified as averantin. This is the first report of its formation by A. parasiticus. Radiotracer studies with [14C]averantin showed that 15.3% of label from averantin was incorporated into aflatoxin B1. This incorporation was blocked by dichlorvos. With radiotracers and other mutants, averantin was placed after norsolorinic acid and before averufin in the biosynthetic pathway in which the general steps are norsolorinic acid leads to averantin leads to averufin leads to versiconal hemiacetal acetate leads to versicolorin A leads to sterigmatocystin leads to aflatoxin B1.

Aflatoxins↗
PubMed1980

Aspects of parasexual analysis in Aspergillus parasiticus.

A scanning electron microscopic examination of the surface ornamentation of haploid, heterokaryotic, and diploid conidiospores of Aspergillus parasiticus is presented. Previous studies on the parasexual cycle in this aflatoxin-producing species have shown that heterozygous diploids may be isolated with ease. However, rational genetic analysis of diploids has been hampered by the nonrandom recovery of auxotrophic markers from heterozygous diploids. In this study, a double transfer method involving only brief exposure to p-fluorophenylalanine (FPA) allowed increased recovery of auxotrophic markers from heterozygous diploids. Extensive sampling of green-spored types from FPA-treated diploids provided an estimate of auxotrophic segregants not visually identifiable. We examined seven heterozygous diploids involving three spore color markers and eight auxotrophic markers. In addition, two mutants blocked in aflatoxin production which accumulated visually detectable aflatoxin precursors were analyzed. One linkage between an auxotrophic marker and a spore color marker was detected; however, no evidence for linkage was found between the blocked aflatoxin mutants and the other markers studied.

Aflatoxins↗
PubMed1979

Influence of trace elements and nitrogen sources on versicolorin production by a mutant strain of Aspergillus parasiticus.

A mutant strain of Aspergillus parasiticus blocked in aflatoxin biosynthesis accumulates versicolorin A and versicolorin C. The effect of trace elements on the growth and versicolorin production by this strain was studied in a defined medium. The omission of manganese was slightly stimulatory to versicolorin production; when zinc was omitted from the medium, no detectable versicolorins were produced. Experiments on nitrogen sources in a high-sucrose medium indicated that fourfold to fivefold increases in versicolorin yields could be obtained by substituting 3 ml/l corn steep liquor or 0.1 M NH4NO3 for the 0.023 M (NH4)2SO3 used previously as the nitrogen source in studies on versicolorin production by this strain. These improved yields will facilitate attempts to accumulate enough versicolorin A and versicolorin C for toxicity and carcinogenicity testing. Chromatographic profiles of mycelial extracts of cultures grown in a defined medium with 0.1 M NH4NO3 as the nitrogen source revealed 2 previously unrecognized compounds. The accumulation of these new metabolites in a mutant blocked in aflatoxin production may indicate that they are biosynthetically related to aflatoxin.

Anthraquinones↗
PubMed1979

Aflatoxins and anthraquinones from diploids of Aspergillus parasiticus.

Three spore colour, two mycelial colour and 12 auxotrophic mutants were isolated from an aflatoxigenic strain of Aspergillus parasiticus. These mutants and heterozygous diploids formed by pairwise combinations of auxotrophs were assayed for aflatoxin production; norsolorinic acid and versicolorin A production were also assayed in the diploids. In general, introduction of an auxotrophic marker lowered aflatoxin production in haploids. The green-spored, prototrophic diploids resembled haploid wild-type strains in that they produced high levels of aflatoxin, low levels of versicolorin A, and no detectable norsolorinic acid. Parasexual analysis of segregants from four heterozygous diploids was hampered by the uniform conidiospore diameter of haploids and diploids and by the non-random recovery of genotypes among somatic segregants with and without treatment with p-fluorophenylalanine. Nevertheless, this technique is useful for recombinational analysis of mutants blocked in aflatoxin synthesis. The fortuitous association of mycelial pigmentation with certain blocked aflatoxin mutants should prove useful in future analyses of the genetics and biosynthesis of these economically important secondary metabolites.

Aflatoxins↗
PubMed1978

Thermal control of blood flow through capillaries and arteriovenous anastomoses in skin of sheep.

Using radioactive microsphere and electromagnetic techniques, hindleg vascular responses were studied in 38 conscious, chronically prepared sheep subjected to either exposure to a warm environment, and/or local warming of the hypothalamus, spinal cord, forelegs of hindlegs. The total proportion of cardiac output passing through AVA's was increased by all treatments. AVA flow in hindleg skin was increased but capillary flow was unchanged by warming the hypothalamus, spinal cord or forelegs. AVA flow was unchanged but capillary flow was increased by warming the ambient air or the hindlegs alone. Equivalent cooling treatments resulted in AVA and capillary flow changes converse to warming. It is concluded that, in sheep, blood flow through cutaneous AVA's is controlled by specific thermoregulatory reflexes, whereas capillary flow is the target of local temperature effects. A significant role for the direction of the thermal gradient across the skin is implicated.

Animals↗
PubMed1978

Radioactive microsphere partitioning of blood flow between capillaries and arteriovenous anastomoses in skin of conscious sheep.

Using radioactive plastic microspheres in conscious sheep, cardiac output is measured by dose injection into a vein, and sampling from the pulmonary artery. Partition of organ blood flow between capillaries and arteriovenous anastomoses is derived from cardiac output and the radioactivity in pulmonary artery blood sampled after dose injection into the artery supplying the organ. Validation tests are presented. The hindlimb is shown to be a suitable model for studying thermal influences on skin blood flow. In contrast to other techniques or previous applications of microspheres: (a) conscious, chronically prepared animals are used, (b) there is no need to kill the animal to obtain results, (c) only small doses are necessary, (d) the one nuclide label can be used repeatedly, and (e) there is no need for precisely matched doses.

Animals↗
PubMed1977

Evidence for the parasexual cycle in a strain of Aspergillus flavus containing virus-like particles.

Eight isolates of A. flavus and A. parasiticus were screened for the presence of virus-like-particles (VLP). Only A. flavus strain NRRL 5565 contained detectable VLP. Spore color and auxotrophic mutants were induced in this strain and evidence for the parasexual cycle was obtained. Attempts to form heterokaryons between 3 auxotrophs of the VLP-containing strain and 9 auxotrophs from two different aflatoxigenic strains were unsuccessful.

Aflatoxins↗
PubMed1976

Effects of acute cold exposure on the distribution of cardiac output in the sheep.

Conscious adult Merino sheep were studied in a thermoneutral environment and then during cold exposure. Microspheres labelled with 141Ce, 51Cr, 85Sr, and 46Sc were used to measure blood flow (Q) in most tissues of the body. (Microspheres labelled with 125I were found to be unsatisfactory.) Cold exposure which caused a marked decrease in skin surface temperature and mild, continuous shivering but no change in deep body temperature, was associated with mean increases in oxygen consumption, heart rate, and cardiac output (C.O.) of 100%, 62%, and 48%, respectively; blood pressure and total peripheral resistance were unchanged. There was approximately a 6-fold increase in Q in perirenal white adipose tissue, and a 3- to 4-fold increase in muscles of the upper foreleg and hindleg, and the intercostals; myocardial Q also increased significantly. There was a marked decrease in Q in skin of the legs and ears, in the maxillo turbinals and in the nasal mucosa, and a decrease in the total proportion of C.O. passing through arteriovenous anastomoses. Thus, not only did C.O. increase, but there was a redistribution appropriate to meet the challenge with which the animal was confronted.

Animals↗