Regulation of zinc homeostatic genes by environmental pH in the filamentous fungus Aspergillus fumigatus.

Aspergillus fumigatus can grow over a broad range of pH values even though zinc availability is greatly conditioned by ambient pH. It has been previously shown that regulation of zinc homeostatic genes in this fungus relies on the transcription factor ZafA. In addition, their expression is further modulated by the transcription factor PacC depending on ambient pH, which allows this fungus to grow in diverse types of niches, including soils and the lungs of immunosuppressed hosts. In this work the regulation by PacC of genes zrfB and zrfC that are expressed, respectively, under acidic and alkaline zinc-limiting conditions have been analysed in detail. Thus, data that extend the current model for PacC function, including the role of the full-length PacC72 protein and the PacC processed forms (PacC53 and PacC27 ) on gene expression has been provided, and a new mechanism for the repression of acid-expressed genes in alkaline media based on interference with the start of transcription has been described. Moreover, it was proposed that the transcription of both acid-expressed and alkaline-expressed genes under zinc-limiting conditions might also rely on a third factor (putatively Pontin/Reptin), which may be required to integrate the action of PacC and ZafA into gene specific transcriptional responses.

Enzymatic hydrolysis as a tool to improve total digestibility and techno-functional properties of pigeon pea (Cajanus cajan) starch.

Recent studies have indicated that starch from legumes can potentially be used as an alternative to commercial flour with applications in food and biomaterials; however, some modifications may be required first to improve their functionality, as they show relatively lower solubility and functional properties compared to commonly marketed flours (e.g. good water retention capacity). This work used multiple enzymes in flour extracts of pigeon pea (Cajanus cajan), a legume, to optimize the enzyme hydrolysis process of such extracts by the Response Surface Method (RSM), to increase the digestibility and obtain desirable functional attributes at the nutritional level. The pH, temperature, time and enzyme/substrate (E/S) ratio were evaluated, and the degree of hydrolysis (DH) was calculated as well as the reducing sugar content (%RS), used as response variable. According to the experimental design, the best pH, temperature, time and E/S ratio were 6.8, 43 °C, 1.84% m/m and 270 min, respectively. The %RS for the samples under optimal conditions was 3.49 ± 0.02%, and the in vitro digestibility yielded values of 39.2 ± 0.4, 58.6 ± 0.3 and 2.2 ± 0.2 for slowly digestible starch (SDS), rapidly digestible starch (RDS) and resistant starch (RS), respectively. Total digestibility (TD) was 97.8 ± 0.5. The statistical analysis revealed a strong positive relationship for E/S ratio followed by pH: (E/S) ratio, temperature and pH. Enzymatic hydrolysis carried out on pigeon pea showed an increase in TD. Viscosity, water retention capacity (WRC) and solubility were evaluated showing good response for future applications at the industrial level.

The interplay between zinc and iron homeostasis in Aspergillus fumigatus under zinc-replete conditions relies on the iron-mediated regulation of alternative transcription units of zafA and the basal amount of the ZafA zinc-responsiveness transcription factor.

Aspergillus fumigatus is a saprophyte fungus that typically grows on organic decaying matter but can also parasitize immunosuppressed hosts. This is explained, in part, by its great ability to take up Zn2+ ions from living tissues, which is induced by the ZafA transcription factor. This study shows that the ZafA-mediated regulation of fungal growth is also influenced by iron availability and that A. fumigatus is well adapted to grow in zinc-limiting and zinc-replete media with Zn:Fe ratios lower in the former than in the latter. Accordingly, this indicates that iron availability appears to be more critical for fungal growth in zinc-replete than in zinc-limiting environments. Interestingly, the cross-regulation of zinc/iron homeostasis under zinc-replete conditions relies on an unprecedented iron-mediated regulation of different zafA transcription units that, along with a limited transcript translation, allows synthesizing the right basal amount of ZafA dependent on iron availability. We posit that this regulatory strategy has evolved in fungi as a mechanism to adjust zinc intake to iron availability under zinc-replete conditions. Thus, fungal growth is enhanced in zinc- and iron-replete media but restricted by reducing zinc intake under iron starvation to prevent the noxious side effects of an intracellular zinc excess during iron deficiency.

The Transcription Factor ZafA Regulates the Homeostatic and Adaptive Response to Zinc Starvation in Aspergillus fumigatus.

One of the most important features that enables Aspergillus fumigatus to grow within a susceptible individual and to cause disease is its ability to obtain Zn2+ ions from the extremely zinc-limited environment provided by host tissues. Zinc uptake from this source in A. fumigatus relies on ZIP transporters encoded by the zrfA, zrfB and zrfC genes. The expression of these genes is tightly regulated by the ZafA transcription factor that regulates zinc homeostasis and is essential for A. fumigatus virulence. We combined the use of microarrays, Electrophoretic Mobility Shift Assays (EMSA) analyses, DNase I footprinting assays and in silico tools to better understand the regulation of the homeostatic and adaptive response of A. fumigatus to zinc starvation. We found that under zinc-limiting conditions, ZafA functions mainly as a transcriptional activator through binding to a zinc response sequence located in the regulatory regions of its target genes, although it could also function as a repressor of a limited number of genes. In addition to genes involved in the homeostatic response to zinc deficiency, ZafA also influenced, either directly or indirectly, the expression of many other genes. It is remarkable that the expression of many genes involved in iron uptake and ergosterol biosynthesis is strongly reduced under zinc starvation, even though only the expression of some of these genes appeared to be influenced directly or indirectly by ZafA. In addition, it appears to exist in A. fumigatus a zinc/iron cross-homeostatic network to allow the adaptation of the fungus to grow in media containing unbalanced Zn:Fe ratios. The adaptive response to oxidative stress typically linked to zinc starvation was also mediated by ZafA, as was the strong induction of genes involved in gliotoxin biosynthesis and self-protection against endogenous gliotoxin. This study has expanded our knowledge about the regulatory and metabolic changes displayed by A. fumigatus in response to zinc starvation and has helped us to pinpoint new ZafA target genes that could be important for fungal pathogens to survive and grow within host tissues and, hence, for virulence.

Micosis superficiales y cutáneas en una población geriátrica de Tunja / Superficial cutaneous mycoses among a geriatric population from Tunja, Colombia

Antecedentes. Las micosis en la población geriátrica son frecuentes, condiciones higiénicas, ambientales y el deterioro del tejido tegumentario facilita su proliferación. Objetivo. Determinar la frecuencia de micosis superficiales y cutáneas que padece la población geriátrica de Tunja, los agentes etiológicos y los factores ambientales, sociales o fisiológicos que posiblemente conllevan a su desarrollo. Material y métodos. Estudio transversal. Entre abril y agosto del 2007 en la Universidad de Boyacá se procesaron 149 muestras procedentes de piel, cabello y uñas de 53 adultos mayores pertenecientes a los Programas “Grupo Revivir”, “Edad Dorada” Asilo San José y hogar geriátrico de Tunja, se realizó encuesta, examen directo a lesiones y cultivo. Resultados. Se identificó los agentes involucrados en el desarrollo de micosis cutáneas en la población geriátrica de Tunja, Candida albicans (27,78 por cento, Trichophyton mentagrophytes, (12,96 por cento), Candida parapsilosis (11,11 por cento) Trichophyton rubrum (7,41 por cento), Scytalidium hialinum (7,41 por cento) Scytalidium dimidiatum (5,56 por cento) Trichophyton sp (3,70 por cento) Candida Krusei (3,70 por cento) Candida rugosa (3,70 por cento) Candida tropicalis (3.70) Fusarium oxysporum (3,70 por cento) Fusarium sp (3,70 por cento) Candida guillermondi (1,85 por cento) Candida sp (1,85 por cento) Cryptococcus sp (1,85 por cento); las micosis de tipo interdigital son las más frecuentes con el 64 por ciento seguida de las onicomicosis (28 por cento), la dermatitis seborreica (5 por cento) y las micosis en pies (3 por cento). Conclusión. Cifras similares en estudios de Antioquia y Valle, se difiere de estudios internacionales. Este primer reporte hecho en población boyacense sugiere mayor atención dermatológica a la población anciana...