Aspochalasins I, J, and K: three new cytotoxic cytochalasans of Aspergillus flavipes from the rhizosphere of Ericameria laricifolia of the Sonoran Desert.

Bioassay-guided fractionation of a cytotoxic EtOAc extract of Aspergillus flavipes occurring in the rhizosphere of Ericameria laricifolia resulted in the isolation of three new cytochalasans, namely, aspochalasins I (1), J (2), and K (3), and four known cytochalasans, aspochalasins C (4), D (5), and E (6) and TMC-169 (7). The structures of compounds 1-3 were established on the basis of extensive 1D and 2D NMR spectroscopic analysis. All compounds exhibited weak to moderate cytotoxicity against NCI-H460, MCF-7, and SF-268 cancer cell lines, but none showed significant selectivity.

Cytotoxic constituents of Aspergillus terreus from the rhizosphere of Opuntia versicolor of the Sonoran Desert.

A novel cyclopentenedione, asterredione (1), two new terrecyclic acid A derivatives, (+)-5(6)-dihydro-6-methoxyterrecyclic acid A (2) and (+)-5(6)-dihydro-6-hydroxyterrecyclic acid A (3), and five known compounds, (+)-terrecyclic acid A (4), (-)-quadrone (5), betulinan A (6), asterriquinone D (7), and asterriquinone C-1 (8), were isolated from Aspergillus terreus occurring in the rhizosphere of Opuntia versicolor, using bioassay-guided fractionation. Acid-catalyzed reaction of 2 under mild conditions afforded 4, whereas under harsh conditions 2 yielded 5 and (-)-isoquadrone (9). Catalytic hydrogenation and methylation of 4 afforded 5(6)-dihydro-terrecyclic acid A (10) and (+)-terrecyclic acid A methyl ester (11), respectively. The structures of 1-11 were elucidated by spectroscopic methods. All compounds were evaluated for cytotoxicity in a panel of three sentinel cancer cell lines, NCI-H460 (non-small cell lung cancer), MCF-7 (breast cancer), and SF-268 (CNS glioma), and were found to be moderately active. Cell cycle analysis of 2, 4, and 5 using the NCI-H460 cell line indicated that 4 is capable of disrupting the cell cycle through an apparent arrest to progression at the G(1) and G(2)/M phases in this p53 competent cell line. A pathway for the biosynthetic origin of asterredione (1) from asterriquinone D (7) is proposed.

Molecular characterization of Embellisia and Nimbya species and their relationship to Alternaria, Ulocladium and Stemphylium.

DNA sequences from rDNA and protein-coding regions were determined for six Embellisia and two Nimbya spp. and were compared to those from Alternaria, Ulocladium and Stemphylium spp. Sequences determined included rDNA from the nuclear internal transcribed-spacer region (ITS1/5.8S/ITS2) and the mitochondrial small-subunit (mt SSU) and a portion of the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene. Phylogenetic analyses were performed on each dataset separately and then combined for total evidence analysis using methods of maximum parsimony and maximum likelihood. Results revealed that Embellisia and Nimbya clustered within a large monophyletic Alternaria-Nimbya-Embellisia-Ulocladium clade with Stemphylium as the sister taxon. Members of the infectoria species-group were the most basal group in this large polygeneric clade. Embellisia and Nimbya were sister taxa of the remaining Alternaria and Ulocladium spp. and were related more closely to Alternaria than was Stemphylium. Four Embellisia spp. formed a monophyletic clade. However, E. allii clustered with the two Nimbya spp. and E. indefessa clustered with Alternaria and Ulocladium spp., revealing that Embellisia, as currently circumscribed, is polyphyletic. Potential revisions of taxonomy for all genera are discussed.

Spatial and Temporal Patterns of Aspergillus flavus Strain Composition and Propagule Density in Yuma County, Arizona, Soils.

Aspergillus flavus isolates from Arizona can be divided into S and L strains on the basis of sclerotial morphology. These genetically distinct strains differ in aflatoxin production. To help understand factors influencing the aflatoxin producing potential of A. flavus communities, spatial and temporal patterns of strain incidence were compared with patterns of A. flavus propagule density in Yuma County soils. Strain S isolates were found in all sampled fields, but the percentage of strain S isolates ranged from 4 to 93%. A nested analysis of variance was used to determine the spatial scale at which most variability in strain composition and propagule density occurred. For both variables, the largest component of variance occurred among fields within areas at a spatial scale of 1 to 5 km. There was also spatial structure (12 to 21% of the variance) at the subregional level (> 20 km) in strain composition, but not in propagule density. Temporal patterns for both variables were similar. The sampling periods with the highest incidence of strain S isolates, August 1994 (60%) and July 1995 (62%), occurred during cotton boll formation. The regional average for A. flavus propagule density was near 1000 propagules/g in the summer, but less than 100 propagules/g in the spring. The results suggest that insights into factors influencing the toxigenicity and propagule density of A. flavus communities might be achieved most readily by contrasting fields in close spatial proximity.