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

Abstract

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 (beta-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.

Insights into Clostridium phytofermentans biofilm formation: aggregation, microcolony development and the role of extracellular DNA

“…It is clear that there are numerous strategies for effective surface attachment, including extracellular polymer production and carbohydrate-binding modules present as part of both cellulosomes and individual cell surface-associated enzymes (Dumitrache et al, 2013a;Kenyon et al, 2005). Such mechanisms demonstrate how surface attachment provides a competitive strategy to acquire substrate where proximity facilitates efficient cellulose hydrolysis and assimilation.…”

Studies of the Extracellular Glycocalyx of the Anaerobic Cellulolytic Bacterium Ruminococcus albus 7

“…Kenyon and Buller (20) demonstrated that the aerobic gram-positive cellulolytic bacterium Cellulomonas flavigena KU produces curdlan, a ␤-1,3-glucan, and that this polymer is a component of the extracellular polymeric matrix of the bacterium during growth on cellulose. Interestingly, C. flavigena produces considerably more curdlan when grown on cellobiose (19), under which conditions the organism grows in a purely planktonic mode and would appear to have little need for an EPS that adheres to cellulose, unless its synthesis was a specific strategy for binding to newly encountered cellulose. By contrast, Mosoni and Gaillard-Martinie (33) reported that R. albus 20 forms only a very thin and irregular glycocalyx during growth on cellobiose.…”

Factors affecting accumulation and degradation of curdlan, trehalose and glycogen in cultures of Cellulomonas flavigena strain KU (ATCC 53703)

“…In contrast, the curdlan EPS produced by C. flavigena KU remains completely cell-associated, and no other EPSs have been detected Kenyon and Buller 2002). Kenyon et al (2005) provided evidence that the curdlan EPS produced by C. flavigena KU may form the basis of an extracellular biofilm matrix involved in cellulose degradation. In addition, there was already substantial proof that extracellular curdlan can serve as a source of carbon and energy for C. flavigena KU , whereas the curdlan produced by other strains of bacteria does (Nakanishi et al 1974).…”

“…Studies by Voepel and Buller (1990) clearly demonstrated that the curdlan EPS can be catabolized by C. flavigena KU if no other source of carbon and energy is available, and therefore, appears to function as an extracellular reserve compound. More recent studies have demonstrated that curdlan EPS is produced during growth of C. flavigena KU on a variety of substrates including cellulose and that the EPS forms the basis of an extracellular matrix promoting biofilm formation (Kenyon et al 2005).…”

“…Intriguingly, C. uda (ATCC 21399) is one of only a few Cellulomonas strains capable of producing large quantities of curdlan EPS Kenyon et al 2005). However, perhaps because of the high nitrogen content of their growth medium (Schimz et al 1983), Schimz and Overhoff did not observe any cellular aggregation indicative of curdlan biosynthesis.…”