Highlighted article: Shi-You Ding, Yu-San Liu, Yining Zeng, Michael E. Himmel, John O. Baker, Edward A. Bayer (2012) How Does Plant Cell Wall Nanoscale Architecture Correlate with Enzymatic Digestibility? Science 23:1055-1060
cell walls stained with phloroglucinol, which stains lignin (not from paper)
I spent three years trying to uncover the various mysteries of plant cell wall architecture without ever considering using an imaging approach. Admittedly, I was a PhD student in a molecular biology group and the necessary microscopy equipment was not exactly under my nose, but Ding et al. (paper published in November’s issue of Science) make such good use of imaging for cell wall research, I am kicking myself for not being as inventive Shi-You Ding and his group at NREL in Colorado, USA.
The paper describes the use of bright-field microscopy, confocal laser scanning microscopy, two-colour stimulated Raman scattering microscopy, and atomic force microscopy to look at the structure of primary and secondary cell walls. The authors were able to follow degradation by bacterial cellulosomes and fungal cellulases of cell walls that were untreated or stripped of lignin.
As the authors say in the abstract, their main conclusions are in support of existing ideas. It has been reasonably well established that lignin is the main barrier to enzyme digestibility, but in my opinion this is the best evidence so far that this is the case. The second conclusion, the theory that leaving the polymers intact as much as possible during pretreatment because damaged micro- or macro-fibres are less effectively hydrolysed than structurally intact ones, is not demonstrated at all in this paper.
For me, there are two results in particular in this paper that are novel and useful. First of all, the atomic force microscopy images in this paper show that the acid chlorite delignification method is an efficient way of stripping away lignin with minimal polysaccharide damage.
Secondly, there is evidence that fungal cellulases use different mechanisms to bacterial cellulosomes, and act more quickly to hydrolyse de-lignified cell walls under the conditions used. Both pieces of information are valuable to cell wall researchers and biofuel producers, and projects like my PhD will run more smoothly because of them.
Image credit: Charis Cook