Effects of UV Irradiation on Penicillium Strains Isolated from a Bread Plant and the Application to Bakery Products.

We tested treatement with UV irradiation for controlling the growth of bread mold. First, we analyzed the sterilizing effect of a dose of approximately 25 mJ/cm2 radiation on nine Penicillium and two Talaromyces strains that were isolated from a bread-manufacturing plant. The P. chermesinum and P. paneum strains were sterilized completely at that dose, while it was only partially effective against P. corylophilum. P. chrysogenum and P. decumbens were sterilized at a dose of approximately 120 mJ/cm2, while T. amestolkiae was sterilized at approximately 150 mJ/cm2. Sterilization of T. cecidicola and P. hispanicum required more than 200 mJ/cm2 of radiation. These results suggest that UV resistance varies depending on the species and the strains. We also carried out UV irradiation of bread at 70 mJ/cm2: a dose at which the taste of bread is not affected; we observed that mold growth was delayed visibly compared to the non-irradiated bread. These results suggest that UV irradiation at 70 mJ/cm2 is effective at delaying mold growth, though it does not cause complete sterilization. This method should prove useful for extending the shelf-life of bread.

Role of the yakA gene in morphogenesis and stress response in Penicillium marneffei.

Penicillium marneffei is a thermally dimorphic fungus and a highly significant pathogen of immunocompromised individuals living in or having travelled in south-east Asia. At 25 °C, P. marneffei grows filamentously. Under the appropriate conditions, these filaments (hyphae) produce conidiophores bearing chains of conidia. Yet, when incubated at 37 °C, or upon infecting host tissue, P. marneffei grows as a yeast that divides by binary fission. Previously, an Agrobacterium-mediated transformation system was used to randomly mutagenize P. marneffei, resulting in the isolation of a mutant defective in normal patterns of morphogenesis and conidiogenesis. The interrupted gene was identified as yakA. In the current study, we demonstrate that the yakA mutant produced fewer conidia at 25 °C than the wild-type and a complemented strain. In addition, disruption of the yakA gene resulted in early conidial germination and perturbation of cell wall integrity. The yakA mutant exhibited abnormal chitin distribution while growing at 25 °C, but not at 37 °C. Interestingly, at both temperatures, the yakA mutant possessed increased chitin content, which was accompanied by amplified transcription of two chitin synthase genes, chsB and chsG. Moreover, the expression of yakA was induced during post-exponential-phase growth as well as by heat shock. Thus, yakA is required for normal patterns of development, cell wall integrity, chitin deposition, appropriate chs expression and heat stress response in P. marneffei.

Comparison of wild-type and UV-mutant beta-glucanase-producing strains of Talaromyces emersonii with potential in brewing applications.

A screen of 46 UV-mutant strains of the moderately thermophilic fungus Talaromyces emersonii yielded two mutants (TC2, TC5) that displayed gross morphological differences to the parent strain and enhanced activity against mixed linkage cereal beta-glucans. Activity against beta-(1, 3)(1, 4)-D: -glucan from barley (BBGase) was measured during growth of the mutant and wild-type strains on a variety of carbon sources, ranging from solka floc to crude cereal fractions. In liquid culture, TC2 and TC5 secreted 1.2- to 8.6-fold more BBGase than the parent strain and markedly less beta-glucosidase (exo-activity); enzyme levels were dependent on the carbon source. Cellulose induced high BBGase. However, beet pulp, wheat bran, carob and tea-leaves were cheap and effective inducers. T. emersonii wild-type, TC2 and TC5 crude enzyme preparations achieved similar end-points during the hydrolysis of commercial barley beta-glucan (13.0-16.9%), but were more active against crude beta-glucan from barley (16.0-24.2% hydrolysis). The products of hydrolysis were quantified by high-performance anion-exchange chromatography. Mash trials indicated that enzyme preparations from all three organisms effected a significant reduction in wort viscosity and residual mash beta-glucan. Finally, TC2 and TC5 produce more efficient beta-glucan-depolymerizing enzymes; and wheat bran and solka floc can be used to provide inexpensive and potent enzyme cocktails with potential in brewing applications.