Developing a method for real-time visualization of cellulase activity

Abstract

Studying the interactions between microorganisms and plant roots is crucial for understanding a variety of phenomena concerning crop yield and health. The role of root surface properties in these interactions, is rarely addressed. To this end, we previously built a synthetic system, from the inert polymer polydimethyl siloxane (PDMS), mimicking the root surface microstructure, using a replication technique. This replica enables the study of isolated effects of surface structure on microorganism-plant interactions. Since the root surface is composed mostly of cellulose, using cellulose-like materials as our replica, instead of PDMS, is the next logical step. This will enable following the hydrolysis of such surfaces as a result of microorganisms secreting Plant Cell Wall Degrading Enzymes (PCWDE), and in particular, cellulase. Visualization of such hydrolysis in a synthetic system can assist in studying the localization and activity of microorganisms and how they correlate with surface microtopography, separately from chemical plant signals. In this work, we modified the known carboxymethyl cellulase (CMC) hydrolysis visualization method to enable real-time tracking of cellulase activity of microorganisms on the surface. Surface was formed from pure CMC, rather than CMC incorporated in agar as is often done, and by that, eliminating diffusion issues. Acridine orange dye, which is compatible, at low concentrations, with microorganisms, as opposed to other routinely used dyes, was incorporated into the film. The dye disassociated from the film when hydrolysis occurred, forming a halo surrounding the point of hydrolysis. This enabled real-time visualization since the common need for post hydrolysis dyeing was negated. Using Root Knot Nematode (RKN) as a model organism that penetrates the plant root, we showed it was possible to follow microorganism cellulase secretion on the surface in the form of CMC film hydrolysis. Furthermore, the addition of natural additives, in the form of root extract was also shown to be an option and resulted in an increased RKN response. We tested our newly developed method by changing temperature and pH conditions and by characterization of the hydrolyzed surface using both Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). This method will be implemented in the future on a root surface microstructure replica. We believe the combination of this new method with our previously developed root surface microstructure replication technique can open a new avenue of research in the field of plant root-microorganism interactions.