# FTIR Spectroscopy for Identification and Intra-Species Characterization of _Serpula Iacrymans_
## 3 Results
### Partial Least Square Discriminant Analysis  
After the acquisition of the FTIR spectra of the different mycelium samples, the data were subjected to min-max and vector normalisation in parallel to determine the most efficient technique. The normalisation data were then processed by the same statistical analysis, PLS-DA.  
Figure 1: Fourier transform infrared (FTIR) spectra of fungi obtained after growth in liquid medium and min-max normalisation. Characteristic spectral ranges corresponding to major macromolecules are indicated by dotted boxes (I, fatty acids; II, proteins; III, polysaccharides and nucleic acids). Each spectrum is the average of at least five spectra obtained after repeating independent experiments under identical conditions.  
The PLS-DA method carried out on the FTIR spectra of the different fungi after growth on the PES membrane and the harvesting of the mycelium allows the classification of the spectra with a percentage of correct attribution of 100% at the level of the phylum, species, and strain for the two methods of data normalisation (Figures 2 and 3).  
The PLS-DA method performed on the FTIR spectra of mycelia after fungal culture on the PES membrane and direct analysis on the membrane (Figure 4) classifies the spectra with a 100% correct attribution percentage at phylum as well as species level for both data normalisation methods. In the case of min-max normalisation, the percentage of correct attribution is 94.44% at the strain level within the species _S. lacrymans_. In this case, 16.7% of the spectra of _S. lacrymans_ UBOCC-A-110074 are attributed to strain _S. lacrymans_ UBOCC-A-110108 and 20% of the spectra of _S. lacrymans_ UBOCC-A-110108 are attributed to strain _S. lacrymans_ UBOCC-A-110074 and 80% of the spectra of _S. lacrymans_ UBOCC-A-110074 are correctly attributed to each of these two strains, respectively. The percentage of correct attribution is 100% for all strains when vector normalisation is performed, indicating a higher efficiency than min-max normalisation for this sample type (Figure 4).  
Figure 3: Confusion matrix obtained for the discrimination of the strains after growth on the PES membrane and scraping the surface of the membrane to harvest the mycelium. Min–max normalization (**A**), Vector normalization (**B**). R. p., Rhodonia placenta. S. l., Serpula lacrymans. T. h., Trichoderma harzianum.  
Figure 2: Confusion matrix obtained for the discrimination of the phylum (**A**) and the species (**B**) after growth on the polyether sulfone (PES) membrane and scraping the surface of the membrane to harvest the mycelium.  
The method is less efficient for identifying fungi when cultured in liquid medium with a variable result according to the type of normalisation (Figure 5). A percentage of the correct attribution at the level of the strain of 80.95% and 99.05% is obtained for min-max and vector normalisation, respectively. After min-max normalisation, 6.7% of the spectra of _S. lacrymans_ LRMH-RX-01 were attributed to _R. placenta_ LRMH-Op-001, which belonged to another species, and the attribution of the spectra of the _S. lacrymans_ strains UBOCC-A-110074, UBOCC-A-110108 and UBOCC-A-111008 were sometimes incorrect, with some spectra being associated with the wrong strain. After vector normalisation, the percentage of correct attribution was 99.05% (Figure 5). In this case, 6.7% of the spectra of _S. lacrymans_ UBOCC-A-110074 were wrongly attributed to _S. lacrymans_ LRMH-SF-EC3-003.