Miguel Ulloa

Cr(VI) reduction in a chromate-resistant strain of Candida maltosa isolated from the leather industry

A Cr(VI)-resistant yeast was isolated from tanning liquors from a leather factory in Leon, Guanajuato, Mexico. Based on morphological and physiological analyses and the D1/D2 domain sequence of the 26S rDNA, the yeast was identified as Candida maltosa. Resistance of the strain to high Cr(VI) concentrations and its ability to chemically reduce chromium was studied. When compared to the three laboratory yeasts Candida albicans, Saccharomyces cerevisiae and Yarrowia lipolytica, the C. maltosa strain was found to tolerate chromate concentrations as high as 100 μg/ml. In addition to this phenotypic trait, the C. maltosa strain showed ability to reduce Cr(VI). Chromate reduction occurred both in intact cells (grown in culture medium or in soil containing chromate) as well as in cell-free extracts. NADH-dependent chromate reductase activity was found associated with soluble protein and, to a lesser extent, with the membrane fraction.

A rapid and simple method for DNA extraction from yeasts and fungi isolated from Agave fourcroydes

A simple and easy protocol for extracting high-quality DNA from different yeast and filamentous fungal species is described. This method involves two important steps: first, the disruption of cell walls by mechanical means and freezing; and second, the extraction, isolation, and precipitation of genomic DNA. The absorbance ratios (A260/A280) obtained ranged from 1.6 to 2.0. The main objective of this procedure is to extract pure DNA from yeast and filamentous fungi, including those with high contents of proteins, polysaccharides, and other complex compounds in their cell walls. The yield and quality of the DNAs obtained were suitable for micro/minisatellite primer-polymerase chain reaction (MSP-PCR) fingerprinting as well as for the sequence of the D1/D2 domain of the 26S rDNA.

Phytotoxic naphthopyranone derivatives from the coprophilous fungus Guanomyces polythrix

Reinvestigation of the fermentation broth and mycelium of the coprophilous fungus Guanomyces polythrix, grown in static conditions, led to the isolation of several phytotoxic compounds, including two new naphthopyranone derivatives, namely (2S, 3R)-5-hydroxy-6,8-dimethoxy-2,3-dimethyl-2,3-dihydro-4H-naphtho[2,3-b]-pyran-4-one and (2S, 3R)-5-hydroxy-6,8,10-trimethoxy-2,3-dimethyl-2,3-dihydro-4H-naphtho[2,3-b]-pyran-4-one. The structures of the new compounds were established by spectral and chiroptical methods. In addition, the structure of 8-hydroxy-6-methyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ester was unambiguously determined by X-ray analysis. The isolates caused significant inhibition of radicle growth of two weed seedlings (Amaranthus hypochondriacus and Echinochloa crusgalli) and interacted with both spinach and bovine brain calmodulins.

Indoor and outdoor airborne fungal propagule concentrations in Mexico City

Thirty homes of asthmatic adults located in Mexico City were examined to determine the predominant culturable fungi and the changes in their airborne concentrations. Fungi were cultured and identified microscopically from air samples collected in naturally ventilated homes, during both wet (July–August) and cool dry (November–December) seasons, and from settled dust from the same homes. Airborne dust from indoor yielded 99–4950 cfu m−3, and settled dust 102–106 cfu g−1 on DG18 agar. The indoor geometric mean concentration of airborne fungi during the cool dry season was 460 cfu m−3 while in the wet season it was 141 cfu m−3. Similarly, numbers of airborne fungal propagules out of doors decreased 60% between the dry and wet season. In general, the total fungal concentrations in indoor air were less than 103 cfu m−3 and a large proportion of them was collected in Stage-2 of the Andersen sampler. Moreover, the ratio between indoor and outdoor concentrations was <3:1. Five of the 30 sampled homes yielded >500 cfu m−3 of one genus, with up to 1493Cladosporium cfu m−3 or 2549Penicillium cfu m−3. Also, these two genera were predominant in both airborne and settled dust, and their concentrations were greater indoors than out, indicating a possible indoor source of fungal propagules. The predominant species wereCladosporium herbarum, Penicillium aurantiogriseum andP. chrysogenum. These results suggest that exposure to large concentrations of fungi occurs indoors and is associated with both seasons of the year and with particular home characteristics.

Isolation and identification of killer yeasts from Agave sap ( aguamiel) and pulque

Wild killer yeasts have been identified as inhibitory to strains used as starters in the production of alcoholic beverages such as beer and wine; therefore, killer or killer-resistant strains have been sought for use in alcoholic fermentations. In the current paper a total of 16 strains belonging to six species were isolated. From two samples of Agave sap (aguamiel) the following yeast strains were isolated: Candida lusitaneae (1), Kluyveromyces marxianus var. bulgaricus (2), and Saccharomyces cerevisiae (capensis) (1). Additionally, in seven samples of pulque (the fermented product), the species C. valida (six strains), S. cerevisiae (chevalieri) (4), S. cerevisiae (capensis) (1), and K. marxianus var. lactis (1) were found. The killer strains were C. valida and K. marxianus var. lactis from pulque and K. marxianus var. bulgaricus from aguamiel. One strain of S. cerevisiae (chevalieri) isolated from pulque which did not show killer activity was, on the other hand, resistant to other killer strains and it had a remarkable ethanol tolerance, suggesting that this strain could be used for alcohol production.

Seasonal distribution of Aspergillus in the air of an urban area: Mexico City

Abstract The seasonal variation of Aspergillus in the atmosphere of Mexico City was determined, using an Andersen air sampler, at different times of the day, over a period of one year. Aspergillus represented a low percentage of the total mould count, 5%, 4%, and 2% in the morning, noon, and night respectively. It was possible only in the morning to observe a seasonal trend for Aspergillus, with high colony numbers during the dry season. However, the highest CFUm-3 were detected in April for the three sampling times of the day. Different percentages of negative growth plates were recorded during the sampling time, but a large percentage was recorded at noon. Multiple regresional analyses indicate that significant correlations exist between Aspergillus CFUm-3 and vapor pressure and temperature inversion in the morning, and with temperature and daily range of temperature at night. Fourteen species of Aspergillus were identified, but A. niger, A. fumigatus, and A. flavus were the most abundant.

Abundance and diversity of microfungi in three coastal beaches of Mexico

The abundance and diversity of species of microfungi was investigated on the beaches of Delfines, Km 24 Veracruz-Alvarado Highway, and El Coco, located on the coasts of the Caribbean Sea, Gulf of Mexico, and the Pacific Ocean, respectively. On each beach a sample composed of sand, subtidal wood or washed-up detritus with moist sand was collected. The samples were analyzed by three different methods, resulting in a total of 1,160 occurrences that fluctuated between 340 and 441 occurrences/sample. The number of species/sample fluctuated between 20 and 32. A total of 52 species was found, of which 12 were marine, and 40 nomarine, of terrestrial origin, and of these 15 were ascomycetes, 34 were hyphomycetes, 2 were blastomycetes and one was a coelomycete. The abundance distribution showed few species with high or low values, with the greates proportion having intermediate values. In order to compare species diversity among the samples frequency curves were utilized, based on the number of species expected from samples taken at random; the results showed that the beach at El Coco was richest in species.

Isolation and identification of killer yeasts from sugar cane molasses

A total of 13 yeast strains were isolated from 10 samples of sugar cane molasses obtained from sugar mills in Mexico; nine of them were killer strains. There was at least one killer strain in every sample. The resulting species were the following: Torulaspora delbrueckii (2), Schizosaccharomyces pombe (7), Cryptococcus albidus var. albidus (1) and Saccharomyces cerevisiae (3). A new killer species is reported: Schizosaccharomyces pombe.

Fungi colonizing hair-baits from three coastal beaches of Mexico

The abundance of hair-bait colonizing fungi was investigated on the beaches of Caracoles, Mocambo, and lcacos, located on the coasts of the Caribbean Sea, Gulf of Mexico and Pacific Ocean, respectively. On each beach a sample of sandy soil was collected. The samples were analyzed by two selective isolation methods for keratinophilic fungi resulting in a total of 544 occurrences. A total of 17 species was found, of which 4 were ascomycetes and 13 hyphomycetes.Gymnascella dankaliensis andAspergillus terreus were the most abundant.Arthroderma curreyi andChrysosporium tropicum were found in low percentages in this survey. From the three beaches sampled, Icacos beach, on the Pacific Ocean coast had the highest number of isolated species.

Guanomyces, a new genus of Ascomycetes from Mexico

A new genus is described to accommodate a species isolated from bat dung. This fungus forms a membranous ascoma with a long neck that is or- namented with lateral glandular hairs and terminal aglandular hairs; filamentous, septate paraphyses and deliquescent asci with hyaline, unicellular ascospores are formed in the base of the centrum. In order to analyze the systematic position of this ascomycete, its morphological characters and 18S rDNA sequences were studied and compared with superficially similar species. Based on morphological and phylogenetic analysis of 18S rDNA sequences, this fungus belongs in the Sordariales and is close to but separate from Chaetomium. The hyaline ascospores, without a germ pore, and the possession of an ascoma with a long neck ornamented with lateral glandular hairs is in contrast to other genera of the Chaetomiaceae. For these reasons, the new genus Guanomyces is proposed to accommodate the new species G. polythrix in the Chaetomiaceae of the Sordariales.