# From Biodeterioration to Creativity: Bioreceptivity of Spruce Pine 87 Glass Batch by Fungi
## 4 Discussion
### Measuring Damage: Two Species, One Glass  
When comparing the behaviours of the two fungi over the same glass substrate, it is possible to observe that: (i) the mycelia over the samples inoculated with _Aspergillus niger_ is less dense than the ones with spores of _Penicillium_ at t\({}_{6}\) in PDA, as spores and even in the contaminated reference samples; (ii) the biopitting and formation of crystals over the surfaces is more pronounced with AS1, in particular when inoculated with the nutritive medium (PDA). The damage patterns differ according to the fungi specimen (_c.f._ Figure 2a), i.e., the _Penicillium chrysogenum_ hyphae fingerprints and craters, stains and iridescence are more visible than the _Aspergillus niger_ ones, and the biopitting and crystals are less dominant in PS1. The inoculated fungi were also able to biodeteriorate SPB-87 glass to different degrees. This behaviour is rather different from what can be observed in the control samples (i.e., early stages of glass alteration), as the authors know well from similar soda-lime silicate glass environmental alteration, that at this point (a maximum of 6 months) has almost negligible damage compared to the one observed in the inoculated samples (e.g., [PERSON] et al. [21], [PERSON] and [PERSON] [36]). The \(\upmu\)-Raman analysis revealed minerals that remained in the glass after the cleaning procedure, something also previously reported [4,6,7]. Most crystalline structures found in our experiment (CaCO\({}_{3}\) and CaC\({}_{2}\)O\({}_{4}\cdot\)H\({}_{2}\)O) are rich in Ca. Nonetheless, the leaching of the bivalent ion Ca\({}^{2+}\) is not usually preferential compared to Na\({}^{+}\) in soda-rich silicate glasses such as SPB-87 [21,37]. [PERSON] and [PERSON] [5] reported that the enrichment of some elements in specific areas can be induced by biomineralisation or produced by the mobilisation of elements by microorganisms. Calcium carbonate (CaCO\({}_{3}\)) is know to be a common water corrosion product widely reported in accelerated or long term ageing, mostly in silicate glass immersion experiments (e.g., [PERSON] and [PERSON] [38], [PERSON] et al. [39]). Short-term or environmental glass alteration experiments in soda-line-silicate glasses (e.g., [PERSON] et al. [21], [PERSON] and [PERSON] [36]) seldom report the presence of this corrosion product in early stages (up to one year exposure), except if pollutants or other external factors are contributing to accelerate the glass surfaces deterioration [40]. The fact that CaCO\({}_{3}\) is present in PS1 and AS1 inoculated samples but is not observed in reference samples, and even less in the control, point to the role of fungi the formation of the observed CaCO\({}_{3}\). It has been well-established, for instance, that the rate of silicate mineral and basaltic glass weathering promoted by environmental microorganisms is usually higher than that of pure chemical weathering [41; 42]. Additionally, other authors already reported the presence of similar biominerals (calcite, kalcinite, and whewellite) in different glass types due to the presence of _Penicillium anantiogriseum_[43]. The main mechanisms underlying microorganisms-silicates interaction have been reported as including: (i) the destruction of the lattice via redox; (ii) the exchange of charge-balancing cations (K\({}^{+}\), Na\({}^{+}\), Ca\({}^{2+}\)) for protons at the surface; and (iii) the production of metabolic by-products (e.g., extracellular enzymes, chelating agents, organic acids), which form network-destabilising surface complexes, or metal complexes [41; 44]. Elements such as Al, Ca, Fe, K, Mg, and Na (released from the material) are assimilated by the biomass [35; 45]. Nonetheless, the crystalline structures and chemical alterations observed here for each fungi present some differences that deserve attention. On the one hand, in the case of AS1, the apparent dissolution and redeposition of elements such as Mg, Zn, and Al increased significantly over time with the growth of the biomass (see Table 3).