Does cellulose II exist in native alga cell walls? Cellulose structure of Derbesia cell walls studied with SFG, IR and XRD

In nature, algae produce cellulose I where all glucan chains are aligned parallel. However, the presence of cellulose II with anti-parallel glucan chains has been reported for certain Derbesia (Chlorophyceae algae) cell walls; if this is true, it would mean a new biological process for synthesizing cellulose that has not yet been recognized. To answer this question, we examined cellulose structure in Derbesia cell walls, intact as well as treated with cellulose isolation procedures, using sum-frequency-generation spectroscopy, infrared (IR) spectroscopy and X-ray diffraction (XRD). Derbesia walls contain large amounts of mannan and small amounts of crystalline cellulose. Evidence for cellulose II in the intact cell walls was not found, whereas cellulose II in the trifluoroacetic acid (TFA) treated cell wall samples were detected by IR and XRD. A control experiment conducted with ball-milled Avicel cellulose samples showed that cellulose II structure could be formed as a result of TFA treatment and drying of amorphous cellulose. These data suggest that the cellulose II structure detected in the TFA-treated Derbesia gametophyte wall samples is most likely due to reorganization of amorphous cellulose during the sample preparation. Our results contradict the previous report of cellulose II in native alga cell walls. Even if the crystalline cellulose II exists in intact Derbesia gametophyte cell walls, its amount would be very small (below the detection limit) and thus biologically insignificant.