ABSTRACT
The secretomes of the strain Cellulosimicrobium cellulans F16 grown on different carbon sources were analyzed by zymography, and the subcellular surface structures were extensively studied by electron microscope. The exo-cellulase and xylanase systems were sparse when cells were grown on soluble oligosaccharides, but were significantly increased when grown on complex and water-insoluble polysaccharides, such as Avicel, corn cob, and birchwood xylan. The cellulosome-like protuberant structures were clearly observed on the cell surfaces of strain F16 grown on cellulose, with diameters of 15-20 nm. Fibrous structures that connected the adjacent cells can be seen under microscope. Moreover, protuberances that adsorbed the cell to cellulose were also observed. As the adhesion of Cellulosimicrobium cellulans cells onto cellulose surfaces occurs via thick bacterial curdlan-type exopolysaccharides (EPS), such surface layer is potentially important in the digestion of insoluble substrates such as cellulose or hemicellulose, and the previously reported xylanosomes are part of such complex glycocalyx layer on the surface of the bacterial cell.
Subject(s)
Actinobacteria/enzymology , Actinobacteria/ultrastructure , Carbon/metabolism , Actinobacteria/metabolism , Bacterial Adhesion , Cellulose/metabolism , Cellulosomes/ultrastructure , Glycocalyx/ultrastructure , Polysaccharides, Bacterial/metabolism , Polysaccharides, Bacterial/ultrastructure , Xylosidases/metabolism , beta-Glucans/metabolism , beta-Glucosidase/metabolismABSTRACT
The hemicellulolytic enzyme system produced by Cellulosimicrobium cellulans strain F16 was resolved by ultracentrifugation and size exclusion chromatography. The particle size and molecular weight were determined by both dynamic light scattering and negative stain electron microscopy. The results showed that xylanosomes produced by strain F16 were found to have an apparent sedimentation coefficient of 28 S, were diverse in size (18-70 nm), molecular weight (11-78 MDa) and morphology, but resembled in subunit composition (SDS-PAGE and proteomic results). It is proposed that particles of 22 nm may be the basic unit, while 43 nm and 60 nm particles observed may be dimer and trimer of the basic unit, or xylanosomes with smaller size might be degradation products of larger size xylanosomes. Moreover, such xylanosomes are also found to have strong binding affinity toward water-insoluble substrates such as Avicel, birchwood xylan, and corn cob.
