Showing papers on "Arabitol published in 2004"

Impact of osmotic and matric water stress on germination, growth, mycelial water potentials and endogenous accumulation of sugars and sugar alcohols in Fusarium graminearum

Abstract: Studies were conducted to determine the effect of osmotic (NaCl, glycerol) and matric (PEG 8000) water stress on temporal germination and growth of two F. graminearum strains over the water potential range of -0.7 to -14.0 MPa at 15 and 25 C. The effect on endogenous water potentials and accumulation of sugars and sugar alcohols also were measured. For both strains, germination occurred rapidly over the same range of osmotic or matric potential of -0.7 to -5.6 MPa after 4-6 h incubation. At lower osmotic and matric potentials (-7.0 to -8.4 MPa), there was a lag of up to 24 h before germination. Optimum germ-tube extension occurred between -0.7 and -1.4 MPa for both strains but varied with the solute used. Growth was optimal at -1.4 MPa and 25 C in response to matric stress, with the minimum being about -8.0 and -11.2 MPa at 15 and 25 C, respectively. In contrast, F. graminearum grew fastest at -0.7 MPa and was more tolerant of solute stress modified with either glycerol or NaCl with a minimum of about -14.0 MPa at 15 and 25 C. A decrease in the osmotic/matric water potential of the media caused a large decrease in the mycelial water potential (Ψ(c)) as measured by thermocouple psychrometry. In general, the concentration of total sugar alcohols in mycelia increased as osmotic and matric potential were reduced to -1.2 MPa. However, this increase was more evident in mycelia from glycerol-amended media. The quality of the major sugar alcohol accumulated depended on the solute used to generate the water stress. The major compounds accumulated were glycerol and arabitol on osmotically modified media and arabitol on matrically modified media. In response to matric stress, the concentration of trehalose in colonies generally was higher in the case of osmotic stress. In each water-stress treatment there was a good correlation between Ψ(c) and total sugar alcohol content.

Polyol accumulation by Aspergillus oryzae at low water activity in solid-state fermentation

Abstract: Polyol accumulation and metabolism were examined in Aspergillus oryzae cultured on whole wheat grains or on wheat dough as a model for solid-state culture. In solid-state fermentation (SSF), water activity (a w) is typically low resulting in osmotic stress. In addition to a high level of mannitol, which is always present in the cells, A. oryzae accumulated high concentrations of glycerol, erythritol and arabitol at relatively low a w (0·96–0·97) in SSF. Accumulation of such a mixture of polyols is rather unusual and might be typical for SSF. A. oryzae mycelium accumulating various polyols at low a w contained at least four distinct polyol dehydrogenases with highest activities toward glycerol, erythritol, d-arabitol and mannitol. NADP+-dependent glycerol dehydrogenase activity correlated very well with glycerol accumulation. A similar correlation was observed for erythritol and NADP+–erythritol dehydrogenase suggesting that NADP+-dependent glycerol and erythritol dehydrogenases are involved in biosynthesis of glycerol and erythritol, respectively, and that these enzymes are induced by osmotic stress.

Osmotic and matric potential effects on growth, sugar alcohol and sugar accumulation by Aspergillus section Flavi strains from Argentina.

Abstract: Aims: The effect of osmotic and matric potential stress on growth and sugar alcohols (polyols: glycerol, erythritol, arabitol and mannitol) and sugars (trehalose and glucose) accumulation in toxigenic and nontoxigenic colonies of Aspergillus flavus and A. parasiticus was evaluated. Methods and Results: Growth of Aspergillus section Flavi with significant reductions at 20 and 30°C was more sensitive to changes in matric potential, between 60 and 100% in the range of −7 to −14 MPa. No significant differences were found between toxigenic and nontoxigenic strains for both species. Total polyol accumulation in unamended maize meal agar medium (−0·75 MPa water potential) was higher at 30 than 20°C. The major change in concentrations of endogenous sugars and total polyols was in matrically amended medium (with PEG 8000) at −7 and −10 MPa. Accumulation of glucose, arabitol, mannitol and erythritol content of A. flavus and A. parasiticus mycelial colonies was greater in normal unstressed maize meal agar medium (−0·75 Mpa) at 20°C. This was modified by solute and matric stress. Conclusions: The data showed relative sensitivity to osmotic and matric potential, and temperature, and the impact on growth rates, polyol and sugar accumulation in mycelia of A. flavus and A. parasiticus. Significance and Impact of the Study: The matric potential effects on growth may be of particular importance for growth and survival in environments with low-matric potential stress. The tolerance of spoilage fungi such as Aspergillus section Flavi to such modifications could increase the potential for spoilage and mycotoxin production in such substrates. This knowledge is important for understanding the relative ecological fitness of these aflatoxigenic species and in the development of prevention strategies for their control.

Metabolite profiles of the biocontrol yeast Pichia anomala J121 grown under oxygen limitation

Abstract: The biocontrol yeast Pichia anomala J121 prevents mould growth during the storage of moist grain under low oxygen/high carbon dioxide conditions. Growth and metabolite formation of P. anomala was analyzed under two conditions of oxygen limitation: (a) initial aerobic conditions with restricted oxygen access during the growth period and (b) initial microaerobic conditions followed by anaerobiosis. Major intra- and extracellular metabolites were analyzed by high-resolution magic-angle spinning (HR-MAS) NMR and HPLC, respectively. HR-MAS NMR allows the analysis of major soluble compounds inside intact cells, without the need for an extraction step. Biomass production was higher in treatment (a), whereas the specific ethanol production rate during growth on glucose was similar in both treatments. This implies that oxygen availability affected the respiration and not the fermentation of the yeast. Following glucose depletion, ethanol was oxidized to acetate in treatment (a), but continued to be produced in (b). Arabitol accumulated in the culture substrate of both treatments, whereas glycerol only accumulated in treatment (b). Trehalose, arabitol, and glycerol accumulated inside the cells in both treatments. The levels of these metabolites were generally significantly higher in treatment (b) than in (a), indicating their importance for P. anomala during severe oxygen limitation/anaerobic conditions.