Clarence S. Buller

The curdlan-type exopolysaccharide produced by Cellulomonas flavigena KU forms part of an extracellular glycocalyx involved in cellulose degradation.

The genus Cellulomonas is comprised of a group of Gram-positive, soil bacteria capable of utilizing cellulose as their sole source of carbon and energy. Cellulomonas flavigena KU was originally isolated from leaf litter and subsequently shown to produce large quantities of a curdlan-type (β-1,3-glucan) exopolysaccharide (EPS) when provided with an excess of glucose or other soluble carbon-source. We report here that curdlan EPS is also produced by Cellulomonas flavigena KU when growing on microcrystalline cellulose in mineral salts-yeast extract media. Microscopic examination of such cultures shows an adherent biofilm matrix composed of cells, curdlan EPS, and numerous surface structures resembling cellulosome complexes. Those Cellulomonas species that produce curdlan EPS are all non-motile and adhere to cellulose as it is broken down into soluble sugars. These observations suggest two very different approaches towards the complex process of cellulose degradation within the genus Cellulomonas.

Structural analysis of the curdlan-like exopolysaccharide produced by Cellulomonas flavigena KU

Cellulomonas flavigena KU produces large quantities of an insoluble exopolysaccharide (EPS) under certain growth conditions. The EPS has previously been shown to be a glucose polymer and to have solubility properties similar to curdlan, a β-1,3-D-glucan produced by Alcaligenes faecalis var. myxogenes 10C3K. Furthermore, EPS purified by alkaline extraction stains with aniline blue, a dye specific for curdlan-type polysaccharides. However, EPS-producing colonies of C. flavigena KU do not stain on aniline blue agar as do those of curdlan-producing bacteria. These facts prompted a more thorough structural analysis of the EPS. Here we report that purified EPS is indeed identical to curdlan in primary structure, but that the native form of the EPS may differ from curdlan in physical conformation. Journal of Industrial Microbiology & Biotechnology (2002) 29, 200–203 doi:10.1038/sj.jim.7000277

Formation of an extracellular energy reserve byCellulomonas flavigena strain KU

SummaryConditions of growth are described which lead to the formation of a dense capsule aboutCellulomonas flavigena and provide data which suggest that, although accumulated as an extracellular structure, it may function as an energy reserve. The capsule is formed when the bacteria are cultured in a minimal medium containing an excess of one of several carbohydrates. The bacterial cells which are encapsulated are also densely aggregated. The capsule is not formed and the cells are not aggregated when the bacteria are cultured in complex growth media. The transfer of aggregated cells to a medium devoid of carbon and energy source results in disappearance of the capsule and disaggregation of the cells.

Production and purification of an extracellular polyglucan produced byCellulomonas flavigena strain KU

SummaryA polysaccharide is synthesized byCellulomonas flavigena strain KU when it is cultured in a synthetic medium which uses ammonium salts as a nitrogen source and contains an excess of a carbon and energy source. Production of the polysaccharide begins in late log phase and reaches a maximimum during stationary phase. In batch cultures it may be produced in yields of up to 9 g dry polysaccharide/liter of culture. It is not secreted into the growth medium but rather remains associated with the cells, resulting, apparently, in their aggregation. When such aggregated cells are extracted with dilute sodium hydroxide solutions the polysaccharide is solubilized. Neutralization of supernatant fluid of such extracts results in sedimentation of the polysaccharide which may then be purified by extensive washing with water. The polysaccharide is insoluble in water, alcohols or acetone, but dissolves in concentrated formic acid, dimethyl-sulfoxide, and dilute sodiumor potassium hydroxide. Thin-layer and gas-liquid chromatographic analysis of hydrolysates indicated that it is a polyglucan. When resuspended in water at concentrations of 2–3% it forms a stable hydrogel.

Isolation and characterization of a new strain ofCellulomonas flavigena

SummaryA cellulolytic bacterium was isolated from leaf litter. Its nutritional characteristics and most of its morphological features closely resemble those of ATCC # 482, which is considered to be the type species ofCellulomonas flavigena (Stackebrandt and Keddie in Bergeys Manual of Systematic Bacteriology). However, when stationary phase cells from cultures using a minimal medium containing an excess carbon and energy source are compared, a very prominent morphological difference is manifest. Phase contrast microscopy and transmission electron microscopy indicate the presence of large swollen polar structures in the type species. The absence of such structures from the new isolate and the production of large amounts of an extracellular polysaccharide indicate that it is a new strain ofCellulomonas flavigena.