Why Solid-State Fermentation Seems to be Resistant to Catabolite Repression?

U ovom radu je dan kritički pregled fenomena otpornosti sinteze enzima na kataboličku represiju pri rastu na čvrstoj podlozi (SSF). U radu se raspravlja o praktičnoj i teorijskoj važnosti tog fenomena. Iznose se ideje koje bi ga objasnile, poput moguće prisutnosti mikroskopskih gradijenata u masi staničnih agregata, ili promjene propusnosti stanica za šećere, koje bi objasnile činjenicu da prisutnost 100 g šećera /L u čvrstoj podlozi tijekom rasta sprječava pojavu kataboličke represije, unatoč tome što u konvencionalnom submerznom uzgoju pri koncentraciji šećera većoj od 10 g/L nastaje jaka inhibicija inducibilnih enzima. Predstavljena su dva alternativna matematička modela za objašnjenje provedivosti tih hipoteza, ali i za planiranje budućih pokusa kako bi se objasnila mikroskopska fiziologija rasta na čvrstoj podlozi. Obje hipoteze objašnjavaju fenomen, ali samo ako se lokalna difuznost ili propusnost šećera tijekom rasta na čvrstoj podlozi toliko promijeni da je različita od one u submerznom uzgoju.A critical review of the phenomenon of resistance to catabolite repression of enzyme synthesis by solid-state fermentation (SSF) has been made. The practical and theoretical importance of such phenomenon is commented, together with the current ideas to explain it. Namely, the possible existence of microscopic gradients within the mass of cell aggregates, or the changes in cell permeability to sugars, which would explain the fact that no catabolite repression is observed in SSF when sugar concentration is as high as 100 g/L, despite the fact that in conventional submerged fermentation (SmF) strong inhibition of inducible enzymes is observed whenever sugar concentration is higher than 10 g/L. Two alternative mathematical models are presented in order to explore the feasibility of those hypotheses, but also to help the planning of future experiments in order to understand the microscopic physiology of SSF. A priori, both hypotheses will explain the phenomenon, but only if the local diffusivity or permeability of sugars in SSF have changed in various orders of magnitude as compared to the observed magnitudes in SmF systems

Abelardo y Eloisa: Dos caras de la misma moneda

Abelardo cavilaba cómo se podría acercar a la bella Eloísa. Y, a través de los chismes de los estudiantes, encontró una solución a su problema. Fulberto, el canónigo tío y tutor de Eloísa, era vanidoso y a la vez mezquino..

REFLEXIONES ANTE LA MEDUSA

Motivadas por el cuadro “Testa de Medusa” de Michelagello Merisi “Caravaggio” durante una visita al museo de los Uffizi en Florencia, Italia, en julio de 2007. Según la mitología, Medusa era una de las tres Gorgonas, de extraordinaria belleza, tenía una magnífica cabellera. Ofendió a Minerva (Atenea) y la diosa transformó a sus cabellos en horrorosas serpientes. Perseo le cortó la cabeza, de la que se servía para petrificar a sus enemigos (Diccionario Enciclopédico Vox

Phosphopantetheinyl Transferase CfwA/NpgA Is Required for Aspergillus nidulans Secondary Metabolism and Asexual Development

Polyketide synthases (PKSs) and/or nonribosomal peptide synthetases (NRPSs) are central components of secondary metabolism in bacteria, plants, and fungi. In filamentous fungi, diverse PKSs and NRPSs participate in the biosynthesis of secondary metabolites such as pigments, antibiotics, siderophores, and mycotoxins. However, many secondary metabolites as well as the enzymes involved in their production are yet to be discovered. Both PKSs and NRPSs require activation by enzyme members of the 4′-phosphopantetheinyl transferase (PPTase) family. Here, we report the isolation and characterization of Aspergillus nidulans strains carrying conditional (cfwA2) and null (ΔcfwA) mutant alleles of the cfwA gene, encoding an essential PPTase. We identify the polyketides shamixanthone, emericellin, and dehydroaustinol as well as the sterols ergosterol, peroxiergosterol, and cerevisterol in extracts from A. nidulans large-scale cultures. The PPTase CfwA/NpgA was required for the production of these polyketide compounds but dispensable for ergosterol and cerevisterol and for fatty acid biosynthesis. The asexual sporulation defects of cfwA, ΔfluG, and ΔtmpA mutants were not rescued by the cfwA-dependent compounds identified here. However, a cfwA2 mutation enhanced the sporulation defects of both ΔtmpA and ΔfluG single mutants, suggesting that unidentified CfwA-dependent PKSs and/or NRPSs are involved in the production of hitherto-unknown compounds required for sporulation. Our results expand the number of known and predicted secondary metabolites requiring CfwA/NpgA for their biosynthesis and, together with the phylogenetic analysis of fungal PPTases, suggest that a single PPTase is responsible for the activation of all PKSs and NRPSs in A. nidulans