Biologia General

Mycorrhizal fungi that form hypogeous sporocarps are an important component of the temperate forest soil community. In many regions, such as the Nothofagus forest in the Patagonian Andes, this group of fungi has been poorly studied. Here we examined the spring and autumn community composition of ''sequestrate fungi'', based on sporocarp production in pure forests of Nothofagus dombeyi (evergreen) and N. pumilio (deciduous). We investigated the possible relationships between these communities and environmental factors over 2 y. The rarefaction curves and the minimal richness estimates converged at nearly the same level for each forest type, and the asymptotes suggested that the sampling effort was sufficient to capture most of the hypogeous sporocarp richness in these forest stands. In total 27 species were recovered. Basidiomycota, Ascomycota and Glomeromycota respectively accounted for nine, two and one genera. Species richness of hypogeous sporocarps varied in relation to forest type but not to season (fall and spring), whereas sporocarp biomass varied according to an interaction between season and forest type. Species richness and sporocarp biomass were positively correlated with rainfall and negatively correlated with altitude. In addition sporocarp species richness was positively related to number of trees per transect. We found that two different forest stands, each dominated by different species of Nothofagus, exhibited different hypogeous sporocarp communities.

We studied the in¯uence of the arbuscular mycorrhizal (AM) non-host plants Stellaria media (Caryophyllaceae), Chenopodium album and Spinaceae oleracea (Chenopodiaceae), Brassica campestris, B. nigra, Capsella bursa-pastoris and Sisymbrium altissimum (Brassicaceae), Juncus balticus (Juncaceae), Urtica dioica (Urticaceae) and of the AM host plant Taraxacum ocinale (Asteraceae) on the colonization of Pisum sativum by the AM fungus Glomus mosseae. None of the non-host plants tested were colonized by Glomus mosseae. Older non-host plants competed with P. sativum. No inhibition of AM colonization was observed in host plants that were grown in the same pot and at the same time as non-host plants. However, when non-host plants were grown for 30 d before P. sativum, they inhibited mycorrhizal colonization of the latter. In a split pot system the presence of U. dioica on the left-side decreased AM colonization of P. sativum roots on the left-side, but not on the right-side. Non-host plants decreased the inoculum potential of G. mosseae and in some cases the percentage AM colonization of host plants cultivated after non-host plants. These results indicate that roots of non-host species have factors that seem to aect the AM fungus before it establishes in the root of host plants. # Soil Biology and Biochemistry 31 0038-0717/99/$ -see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 8 -0 7 1 7 ( 9 9 ) 0 0 0 8 7 -5

The mycorrhizal status of plant species in north-west Patagonia was examined. Communities representative of Patagonian steppe and marshes were compared with respect to the mycorrhizal status of their species. Most of both native and exotic plant species sampled were arbuscular mycorrhizal (AM). The percentage of species with mycorrhizal association was higher for perennial herbs and shrubs than for annual herbs. The higher ratio of mycorrhizal/nonmycorrhizal (NM) species found for dicotyledons than for monocotyledons, could reflect the presence of a considerable number of NM monocotyledons in the marsh. The mycorrhizal status of plants differed slightly between the steppe and the marsh. In the steppe, native AM species were more frequent than in the marsh. In contrast, in the marsh, the NM species were proportionally more represented than in the steppe. The Juncaceae and Cyperaceae, which include hydrohytic NM plants, accounted for many of these differences. Moreover, the dominant s...

Aims: Dekkera bruxellensis and Pichia guilliermondii are contaminating yeasts in wine due to the production of phenolic aromas. Although the degradation pathway of cinnamic acids, precursors of these phenolic compounds has been described in D. bruxellensis, no such pathway has been described in P. guilliermondii. Methods and Results: A molecular and physiological characterization of 14 D. bruxellensis and 15 P. guilliermondii phenol-producing strains was carried out. Both p-coumarate decarboxylase (CD) and vinyl reductase (VR) activities, responsible for the production of volatile phenols, were quantified and the production of 4-vinylphenol and 4-ethylphenol were measured. All D. bruxellensis and some P. guilliermondii strains showed the two enzymatic activities, whilst 11 of the 15 strains of this latter species showed only CD activity and did not produce 4-EP in the assay conditions. Furthermore, PCR products obtained with degenerated primers showed a low homology with the sequence of the gene for a phenyl acrylic acid decarboxylase activity described in Saccharomyces cerevisiae. Conclusions: D. bruxellensis and P. guilliermondii may share a similar metabolic pathway for the degradation of cinnamic acids. Significance and Impact of the Study: This is the first work that analyses the CD and VR activities in P. guilliermondii, and the results suggest that within this species, there are differences in the metabolization of cinnamic acids.

An ecological study of Saccharomyces cerevisiae strains in spontaneous alcoholic fermentation has been made in the same winery on two consecutive years (1993 and 1994) with Merlot type musts, and with Malbec type must on a third year (1998). Saccharomyces cerevisiae strains associated with winery surfaces were also analysed. Differential killer sensitivity patterns related to a killer reference panel of 10 killer yeasts belonging to nine species of four genera were used as a quick and simple procedure to discriminate between indigenous S. cerevisiae isolates at the strain level. Although a great diversity of wild strains was observed, two main indigenous S. cerevisiae strains, designated as S. cerevisiae 9 and S. cerevisiae 13, took over the Merlot type fermentation in both years. These strains also appeared in Malbec must fermentation during the year 1998 and they were again found on the winery surface the next year. These results show that some few and stable indigenous S. cerevisiae strains remained in the environmental winery over the considered period of time (1993–1999) and they represent an additional evidence of the taking over of musts by local strains of S. cerevisiae.

Pichia guilliermondii can produce volatile phenols in the initial stages of wine fermentation; however, its response to different wine stress conditions has been poorly studied. In this work, we present an analysis of the response of 23 P. guilliermondii indigenous isolates to physical and chemical wine stress factors and to indigenous wine killer yeasts. Principal coordinates analysis (PCoA), based on data obtained from response patterns, was carried out to evaluate the relationships among the isolates. Major differences among the isolates were detected in media plates containing 8% ethanol and in those containing 280 g/L glucose. PCoA identified 3 clusters of isolates with different stress response patterns, indicating a relationship between the tolerance to these compounds and the origin of the isolates. Pichia guilliermondii isolates were sensitive to the toxins produced by the species Hanseniaspora uvarum, Metschnikowia pulcherrima, Wickerhamomyces anomala (ex Pichia anomala), and Pichia kluyveri, with a maximum level of sensitivity against W. anomala (91% on average). Those isolates obtained from fermenting must proved to be more resistant to killer yeasts than those obtained from grape surfaces. The combined evaluation of the response to physico-chemical and biological factors presented in this work could be a useful standard protocol for the evaluation of the potential spoilage capacity of yeasts in winemaking.

The diversity and killer behaviour of the yeast biota associated with surfaces of four Patagonian wineries were analyzed in the present study. These wineries were different in their technological and ecological features. Following liquid enrichment of samples from fermentation vat surfaces yeast isolates were identified by pheno-and genotyping and characterized using killer sensitivity patterns. Out of 92 isolated yeasts, 25% were Saccharomyces cerevisiae; 18% were Kloeckera apiculata and 11% were Pichia anomala; other six species representing a low percentage were also found. A particular biota composed mainly by S. cerevisiae (57%) and P. anomala (37%) was found in the winery located far from the other three wineries. As a whole, the wineries using spontaneous fermentation showed a major percentage of S. cerevisiae and a minor percentage of K. apiculata. The present study showed a pronounced heterogeneity in killer behaviour: killer, 35%, neutral, 25% and sensitive, 40%. In particular, S. cerevisiae isolates showed a higher sensitivity to killer reference yeasts than non-Saccharomyces isolates. On the other hand, most of the non-Saccharomyces yeasts isolated from fermentation vats were resistant to Saccharomyces toxins.

Aims:  To investigate whether the presence of Pichia guilliermondii impacts on the production of volatile phenols from mixed wine fermentations with Dekkera bruxellensis and Saccharomyces cerevisiae.Methods and Results:  Four inoculation strategies were performed in small-scale fermentations involving P. guilliermondii, D. bruxellensis and S. cerevisiae using Syrah grape juice supplemented with 100 mg l−1 of p-coumaric acid. High pressure liquid chromatography was used for the quantification or volatile phenols. Significant high levels of 4-ethylphenol and 4-ethylguaicol (720 and 545 μg l−1, respectively), as well as the highest levels of 4-vinylphenol (>4500 μg l−1), were observed when P. guilliermondii species was inoculated from the beginning of the fermentation.Conclusions:  The metabolic interaction occurring between the high vinylphenol producer species P. guilliermondii and D. bruxellensis exhibiting a high vinylphenol reductase activity resulted in an increased production of volatile phenols in wine.Significance and Impact of the Study: Pichia guilliermondii must be considered a very important spoilage yeast in the wine industry capable of producing large amounts of volatile phenols.

In order to detect spoilage yeast species in wines showing off-odors, different yeast isolation protocols were evaluated. Independently of the isolation method, only Saccharomyces cerevisiae and Pichia manshurica were detected. The spoilage capacity of P. manshurica regional isolates was evaluated in red wine and the production of volatile phenols was evidenced. To evaluate the possible source of contamination, yeasts from both grapes and cellar surfaces were obtained. Hanseniaspora uvarum and Zygoascus hellenicus were detected in both sound and damaged grapes from sunny areas. The most frequent species in cellar surfaces was Candida boidinii, Pichia membranifaciens and P. manshurica were detected in filters. The intra-specific genetic characterization of the P. manshurica isolates by mtDNA-RFLP demonstrated that the same strain was detected in both wine and filter. Most P. membranifaciens isolates produced 4-EP (maximum level of 1.895 mg/L) and particularly high levels of 4-EG (maximum level of 10.260 mg/L) were produced by P. manshurica isolates in synthetic wine-like medium. In this work the capacity of P. manshurica and P. membranifaciens species to produce volatile phenols was shown for the first time.

Putative mechanisms of action associated with the biocontrol capacity of four yeast strains (Cryptoccocus albidus NPCC 1248, Pichia membranifaciens NPCC 1250, Cryptoccocus victoriae NPCC 1263 and NPCC 1259) against Penicillium expansum and Botrytis cinerea were studied by means of in vitro and in situ assays. C. albidus (YP) , a commercial yeast was also evaluated for comparative purposes. The yeast strains exhibited a variety of different mechanisms including: wound colonization, germination inhibition, biofilm formation, secretion of killer toxins, competition for nutrient and secretion of hydrolytic enzymes (protease, chitinase and glucanase). The relationship between strains (and their associated antagonist mechanisms) and in situ antagonist activity was also evaluated. Results indicate that mechanisms such as production of hydrolytic enzymes, the ability for colonization of wounds, production of killer toxin and inhibition of germination are the most important for biocontrol activity. Our study indicate that multiple modes of action may explain why P. membranifaciens NPCC 1250 and C. victoriae NPCC 1263 provided excellent control of postharvest pears disease.

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The term radio-adaptive response (AR) applies to the phenomenon of protection or enhanced repair induced by a low radiation dose. Blood microcultures from 4 donors were irradiated to test the existence of AR in human lymphocytes using two different irradiation schemes. An adapting dose of 0.01 Gy and a challenging dose of 1.5 Gy of gamma radiation from a 2.5 MeV LINAC was used in all experiments. A cytogenetic analysis of unstable chromosome aberrations was applied as the endpoint. An inter-individual variability response was observed in one of the irradiation schemes: one donor expressed AR, two did not and the last showed an apparent synergistic response. The other irradiation scheme showed low mitotic indices (MI), suggesting a G2 arrest.

Palabras clave: calidad seminal, inseminación artificial, ovinos, fertilidad, semen congelado RESUMEN Se analizó la relación entre la calidad del semen post-descongelamiento y la eficiencia reproductiva en ovinos Merino. Se utilizó semen congelado de 10 carneros en una majada de 645 ovejas adultas. Se sincronizaron los estros mediante esponjas vaginales con progestágenos y una dosis de 300 UI de eCG (gonadotrofina coriónica equina). A las 60±2 horas post tratamiento progestacional, se efectuó la inseminación artificial intrauterina por laparoscopía sistemática (IALS). Se evaluó la calidad seminal post-descongelamiento mediante las siguientes pruebas: movilidad masal microscópica (MMm), movilidad individual progresiva (MIP), porcentaje de espermatozoides vivos (PEV) y el test hiposmótico (Host). Se determinó el número total de espermatozoides (NTE). La correlación entre MMm y MIP evidenció una asociación significativa (P< 0.05). Las correlaciones entre MMm y PEV, y entre MMm y Host no fueron estadísticamente significativas (P> 0.05). El PEV se relacionó significativamente con la MIP y con el Host, los que a su vez presentaron una correlación significativa entre sí. Los análisis de regresión lineal simple determinaron que la variabilidad de la eficiencia reproductiva, expresada como el porcentaje de preñez por carnero, puede ser explicada significativamente por los valores de MIP y de PEV. La MMm y el Host no permitieron explicar la variabilidad de la fertilidad del semen. El análisis de regresión lineal múltiple, conjuntamente con el método de selección Stepwise, determinó que la MIP (R2 = 0.67, P = 0.0036) fue lo que mejor explicó la variabilidad observada en la eficiencia reproductiva obtenida en la IALS.