# From Biodeterioration to Creativity: Bioreceptivity of Spruce Pine 87 Glass Batch by Fungi
## 3 Results
### Surface Morphology: Optical and Scanning Electron Microscopy  
Glass samples were examined by optical and scanning electron microscopy after 4- and 6-month incubation periods (t\({}_{4}\) and t\({}_{6}\), respectively) to assess the glass surfaces' morphology \begin{table}
\begin{tabular}{l l l} \hline \hline
**Strain nr.** & **Nearest Homologue (Accession Number)** & **Similarity (\%)** \\ \hline PS1 & _Penicillium chrysogenum_ UWR\_107 ITS region (KY465761) & 100\% \\  & AN TYPE fungus (NR\_077145) & \\ AS1 & _Aspergillus niger_ OR32F12 ITS region (MT510013) & 100\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Taxonomic classification of the fungal strains. and to detect the expected biocorrosion products. Optical microscopy allowed us to observe the glass surfaces and the associated mycelium growth, aesthetic and chromatic alterations, and the biocorrosion patterns in comparison with the non-inoculated samples. A summary of the results is presented in Figure 2 (and in more detail Appendix A, Figure A2), and it is shown each type of inoculated surfaces before (left column) and after the cleaning procedure (right column), for t\({}_{4}\) and t\({}_{6}\) periods of incubation. Over in both PDA and spores in Tween inoculation with _Penicillium chrysogenum_ (PS1), biological colonisation was clearly observed on both types of surfaces. Growth and densification of mycelium occurred between 4 (t\({}_{4}\)) and 6 months (t\({}_{6}\)) after the inoculation. Staining, etching, biopitting, and crystal formation were also observed, even after the cleaning procedure (Figure 2 and Appendix A, Figure A2a, marked as 'B', 'E', and 'F', respectively). The darkening of glass surfaces from deterioration processes is often associated with fungal growth [19]. _Penicillium chrysogenum_ spores produced biological colonisation and mycelium growth (with hyphae reaching the edges) in all glass samples (Appendix A, Figure A2b). These surface alterations (including crystal formation) increased over 6 months. At t\({}_{6}\), the hyphae fingerprints were visible even after performing the cleaning procedure in all inoculated samples (Figure 2), showing that fungal mycelium was strongly anchored on the glass surface. Therefore, it is not surprising to verify that _Penicillium chrysogenum_ spores inoculation produced a mycelium density smaller than the inoculated _Penicillium_ in PDA. Hence, in  
Figure 2: Optical microscopy results from (**a**) the inoculation of SPB-87 with _Penicillium chrysogenum_ and _Aspergillus niger_, and of (**b**) the reference samples placed inside the same conditions of the inoculation environment. Legend: (A) clear biological colonisation/mycelium, (B) chromatic alterations (spots, stains, iridescence), (C) mycelium growth up to the edge, (D) denser mycelium near the PDA, (E) Etching/biopitting produced by hyphae, (F) crystal formation, (G) growth of mycelium from the spores. this case, the nutritional source plays an important role in the fungal growth, although it is not a limiting factor, since fungal growth was observed for all cases. Observations of the surfaces inoculated with _Aspergillus niger_ shown in Figure 2 (and in more detail in Appendix A, Figure A3) also revealed that all samples with PDA showed biological colonisation and mycelium growth after 4 months of incubation (Figure 2a, and Appendix A, Figure A3a for more detail). However, hyphae do not reach the sample edges, in contrast to what occurred with samples inoculated with _Penicillium chrysogenum_ (Appendix A, Figure A2a). Biopitting and crystal formation was also observed at t4 for _Aspergillus niger_ in PDA ('E' and 'F' in Figure 2a and Appendix A, Figure A3a), similar to what was observed in the case of _Penicillium chrysogenum_ (Appendix A, Figure A2a). After 6 months, all samples inoculated with _Aspergillus niger_ samples showed a mycelium density similar to t4, which was less dense than the one observed for the _Penicillium chrysogenum_ one.