RESUMO
A number of 21Aspergillus sp. strains isolated from cowpeas from Benin (Africa) were characterized by RAPD methodology. Seven of these strains grouped withA. flavus in the dendrogram generated with the RAPD data. Only three were able to produce aflatoxin in significant amounts. Twelve other isolates grouped withA. parasiticus. All of these strains except 3 produced aflatoxin. Two additional strains neither fit with theA. flavus group, nor theA. parasiticus group according to their RAPD pattern. Both did not produce aflatoxin in measurable amounts.Generally the aflatoxin positive strains produced high amounts of aflatoxin after growth on YES medium. However after growth on cowpea based medium aflatoxin biosynthesis was strongly ceased, albeit the growth of the colony was only partly reduced. This was true for media made either with the whole cowpea seed or with cowpea seed without seed coat. Interestingly when the cowpea medium was heat sterilized the fungus was able to produce high amounts of aflatoxin. This, however, was not the case after the use of gamma irradiation as sterilization method for the medium. The expression of thenor- 1 gene, which is one of the early genes involved in aflatoxin biosynthesis, was significantly repressed after growth on gamma irradiated cowpea medium in contrast to YES medium.
RESUMO
The O-specific polysaccharides of Xanthomonas campestris pv. vignicola GSPB 2795 and GSPB 2796 were studied by sugar and methylation analyses, Smith degradation, ID, 2D 1H and 13C NMR spectroscopy. It was found that the polysaccharides are similar branched D-rhamnans lacking strict regularity, and their structures can be described as follows: [carbohydrate equation: see text] where Rha(v) is present in a non-stoichiometric amount, which varies from strain to strain.
Assuntos
Desoxiaçúcares/química , Espectroscopia de Ressonância Magnética , Mananas/química , Antígenos O/química , Xanthomonas campestris/química , Sequência de Carboidratos , Dados de Sequência MolecularRESUMO
The O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. manihotis strains GSPB 2755 and GSPB 2364 was studied by sugar and methylation analyses and 1H and 13C NMR spectroscopy, including 2D COSY, TOCSY, NOESY, and H-detected 1H, 13C heteronuclear multiple-quantum coherence (HMQC) experiments. The polysaccharide was found to contain L-rhamnose and L-xylose in the ratio 3:1, and the following structure of the tetrasaccharide repeating unit was established: [formula: see text]
