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134    Cha pte r  F i v e


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        Major differences have been found as hyphae mature;  differences
        between strains and species may be identified and interpreted in
                                            51
        terms of cell morphology and physiology.  Since the spatial resolu-
        tion achievable with sFTIR is typically an order of magnitude poorer
        than that of Raman, and since the information turns out to be quite
        different also, we deal with the each separately.

        5.4.1  Physical Considerations and Spectral
                Anomalies in sFTIR Spectra
        The walls of fungal hyphae are composed primarily of cross-linked sug-
        ars; the hyphae may be hundreds of micrometers in length, but are typi-
        cally only a few micrometers in diameter. Hence, their physical structure
        presents some challenges for FTIR imaging. We have acquired all our
        fungal FTIR spectra described here with synchrotron-source IR light, on
        instruments setup for single pixel or raster scanning.
            The differences between the mature regions of hyphae of three
        fungi, A. nidulans, Neurospora, and Rhizopus, are readily apparent in
                                                    9
        their sFTIR spectra, Fig. 5.3; see also Szeghalmi et al.  The A. nidulans
        hyphal width is about 3 μm, compared to up to 10 μm for the others.
        The mature hyphal walls, which are rich in cross-linked sugars,
        exhibit pronounced differences in number, energy, and relative inten-
                                                  –1
        sity of bands in the sugar region (900 to 1200 cm ). The CH-stretch
                             −1
        region (2800 to 3000 cm ) also shows marked differences between
                               −1
        species. The peak at 2854 cm  is a marker for CH stretch (characteristic
                                                2
        of membrane lipids) and is expected to be present surrounding the cell
        organelles. The CH bonds in the sugar molecules will also contribute
             2922
      0.7                1.0      1632
                         0.9          1527
      0.6
           2954  2876  2854  0.8  1738  1532            1015  988
      0.5    2925        0.7      1645                 1034

      0.4  2958    Rhizopus  0.6   1626  1452  1389  1147  1109  1078  963
     TR                  0.5     1648
      0.3       2873  2854  0.4  1738  1537        1148  1112  1077  1037  1018  990  Rhizopus
      0.2         Neurospora  0.3       1455
           2956  2926    0.2                               Neurospora
      0.1       2873  2855                         1154  1108  1072
                  Aspergillus  0.1
                                                           Aspergillus
      0.0                0.0
       3000       2800     1800   1600   1400   1200   1000
                  –1                             –1
        Wavenumber (cm )               Wavenumber (cm )
   FIGURE 5.3  IR spectra of hyphae from three different fi lamentous fungi: Aspergillus
   nidulans, Neurospora, and Rhizopus. Note that the intensity of Neurospora
   spectrum is fi ve-fold increased, for clarity of visual comparison. (Reproduced from
   Ref. 9, with permission of Springer Verlag.)
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