Position-dependent changes in phycobilisome abundance in multicellular cyanobacterial filaments revealed by Raman spectral analysis

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The one-dimensional filamentous cyanobacterium, Anabaena sp. PCC 7120, shows a simple pattern consisting of two types of cells under the nitrogen-deprived conditions. We found that the microbial pigment composition in differentiated (heterocyst) and undifferentiated cells (vegetative cells) were distinguished by using a Raman microscope. The Raman bands of phycocyanin and allophycocyanin were higher in the vegetative cells than those in the heterocysts. However, these bands were statistically lower in a part of vegetative cells, which were located far from a nearby heterocyst. That is, the pigment composition in the individual cells was affected by a locational information in a filament.

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  1. In fact, we confirmed that one of the cells a–g was finally differentiated into a heterocyst.

    Where is the data that supports this claim that one of the vegetative cells differentiated into a heterocyst?

  2. selecting the central points of the cells.

    Were any measurements made across the cell using parameters for the maximal spatial resolution (0.25 µm)? It would be good to note (in a supplemental figure perhaps) that there was no difference across the 3 µm cell and justify using the center point of each cell for all of the measurements.

  3. To interpret the Raman spectra, as well as the positional differences in the spectra along the filaments, it would be helpful to the reader to see images of the filaments. How do the spectra relate to the images of the filaments?