Isolation and Identification of Thermophilic Fungi

We isolated thirty thermophilic fungi with ability to grow at 45 °C on medium containing wheat bran and casein as carbon sources and produced proteases in both SSF and SmF (data not shown). The fungus strain F.2.1.4 presented the highest protease activity and was sub-jected to taxonomic characterization.

Analyses of macro and micro-morphological characteristics accommodated the isolate F.2.1.4 in the genus Myceliophthora due to the presence of spreading colonies with dense aerial mycelium and blastic conidia often borne in ampulliform swellings (Van Oorschot, 1980). Particularly, this isolate produced pulverulent pale mycelium, obovoid conida measuring 5.65-7.91 x 3.39-4.52 μm as well as conidia walls finely ornamented. Based on such char-acters the isolate F.2.1.4 is similar to Myceliophthora thermophila, however, some slight morphological differences were observed, for instance, M. thermophila has pale brown, woolly colonies and a variable range of conidia sizes 4.5-11 x 3.0-4.5 µm (Van Oorschot, 1977).

Data derived from BLAST (ITS-rDNA region) showed that the isolate F.2.1.4 had high sequence similarities (99-96%) with three unidentified Myceliophthora spp. isolated from geothermal soils in China; and 95-94% of sequence similarities with different strains of the Ascomycota genus Corynascus (one of the Myceliophthora teleomorphic states), includ-ing three new species: C. verrucosus sp. nov., C. similis sp. nov., C. sepedonium, C. sexualis sp. nov. (Stchigel et al., 2000). The phylogenetic tree showed that the isolate F.2.1.4 clustered with the three Myceliophthora strains from China (Figure 1).

Molecular and phylogenetic results corroborate the data from morphological analyses and considering the combined methods used for f...

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...ease immobilized in the alginate beads

When comparing the performance of immobilized biocatalysts intended for industrial use, knowledge of their operational stability is very important. The stability of an immobilized enzyme without appreciable loss of enzyme activity is important mainly for the economic viability. Figure 5 shows the effect of repeated use on the activity of the immobilized prote-ase; it decreased gradually during 7 cycles of reuse (being its activity at the 7th cycle above 50% of the original activity) and more sharply after that.

In conclusion, the thermophilic fungus Myceliophthora sp. was able to produce alkaline and thermostable proteases in SSF using wheat bran as culture medium. The protease immobilization in alginate not only maintained some properties, but improved strongly its thermal stability and permitted its reuse for seven cycles.