## 1 Introduction  
Many bacteria produce extracellular polysaccharides (EPS) that are involved in attachment. EPS enable cell-cell attachment, facilitating the formation of flocs (rafts of aggregated cells in aqueous environments) and biofilms through enhancing attachment to surfaces in soils or on plants and animals. In pathogenesis they may confer resistance to host defenses [1], thereby promoting intracellular survival [2]. In non-pathogenic contexts, they may increase access to nutrients and protect against environmental stresses (e.g., desiccation and toxic agents) [3, 4]. Some EPS are hydrophilic or gel forming polymers and are loosely adherent to the bacterial surface forming a slime layer (e.g., xanthan from _xanthomas__ampstris_ and succinoglycan from _rhizobia_ and _agrobacterium_ species). Others form a discrete capsule, which overlies the cell surface but is not attached to it (e.g., hyaluron from _streptomycinococcus_ species and _pasteurella__mulucida_[5, 6]). In _azotobacter__vinelandai_ a calcium alginate gel forms a coat around the resting cyst stage [7]. Some bacteria are known to produce several different EPSs simultaneously, such as _agrobacteriumum tumefaciens_, which can produce at least five [8]. A few EPS are water-insoluble, notably the (1-4)-\(\beta\)-glucan, cellulose, e.g., _gluconacetobacter xylinus_[9], _agrobacteriumum tumefaciens_[8], species of _pseudomonas_, _chromobacter_,alalaligenes, rhizobium, azotobacter_[10], members of the enterobacteriaceae [11; 12], and as a sheath around filamentous cyanobacteria [13]. Curdlan, a linear (1\(\rightarrow\)3)-\(\beta\)-D-glucan, is another example of a water insoluble EPS. This polysaccharide is produced by various _agrobacterium_ species [14], some rhizobium isolates [6], the gram-positive _cellulomonas flavigena_[15; 16] and an isolate of _rahmella variigena_, a member of the enterobacteriaceae family [17]. Interestingly, in all cases cited above, curdlan production in the laboratory requires N-limited culture medium with ample carbohydrate, which fits with the general observation that the production of EPS [18; 19; 20; 21; 22], as well as the internally stored polyhydroxyalkanoates [23] are frequently induced by nutritional stress, e.g., N, P or S limitation. It is nonetheless remarkable that the capacity for curdlan production is not restricted to a single class or even a phylum (e.g., gram-negative), but rather to a handful of bacteria that seem related only by their soil habitat. So far, curdlan production has only been detected in rhizosphere-dwelling bacteria, and is in every case regulated by N-limitation. The biological role of curdlan has not been demonstrated, but it has been suggested to help form a biofilm that protects against predation, starvation, and desiccation [8]. Such a role is consistent with microscopic observations of _C. flavigena_[24], a soil-dwelling, curdlan-producing bacterium that colonizes and decomposes plant material using cellulose as a source of carbohydrate. However, little information is available on the form of nascent curdlan, its deposition, and the ongoing nature of its interaction with the cell surface. Curdlan is occasionally referred to in the literature as a capsule, although clear evidence for a capsular form has not been provided. Curdlan-producing _agrobacterium_ strains grown on glucose-rich yeast extract agar medium produce a coherent, aniline blue-staining, pellicle which may be stripped from areas of confluent bacterial growth [14], giving the appearance of curdlan deposition as a disorganized mass at the colony surface. However, such an appearance does not rule out the possibility of a capsular form. One possibility is that curdlan is produced as a discrete capsule by some cells located strictly in the periphery of a biofilm. This scenario takes into account the strong dependency of curdlan production on oxygen availability [25]. Peripheral cells would, in this way, have the role of providing curdlan as a protecting layer for the whole population.