At this point of time, strain AH-1N had reached 5-fold and 8.7-fold lower CFU numbers in the suspended and in the biofilm fraction, respectively, compared to the single culture (Fig. 2a). In contrast, strain

4D9 reached 34-fold higher CFU numbers in the suspended and 13 700-fold higher CFU numbers in the biofilm fraction compared GKT137831 mw to its single culture (Fig. 2a). Growth of strain 4D9 in the biofilm fraction of the co-culture was visible by the formation of its characteristic orange colonies on the surface of the agarose beads (Fig. 2b). These colonies turned red upon treatment with KOH, indicating the presence of the pigment flexirubin, which is characteristic for bacteria of the Cytophaga/Flavobacterium group (Reichenbach et al., 1980). Apparently, strain 4D9 was able to grow especially in the biofilm fraction of the co-culture even though it could not degrade embedded chitin itself, and it even overgrew strain AH-1N. The strong growth stimulation of strain 4D9 in the biofilm fraction could be the

outcome of different strategies. First, strain 4D9 might have been able to access chitin within the selleck products agarose bead by penetrating into cavities within the agarose that had resulted from chitin degradation. However, as strain 4D9 only grew on the periphery of the agarose beads, (Fig. 2b) this was unlikely. Second, strain 4D9 might have grown with organic substrates that were released by strain AH-1N. These could have been either chitin degradation products or other substrates. To identify the substrates causing the strong growth stimulation of strain 4D9 in the

biofilm fraction of the co-culture, it was first analyzed, which compounds were released during growth of strain AH-1N with embedded chitin in single cultures. These analyses revealed that acetate and ammonium were transiently released, while GlcNAc and its oligomers could not be detected (not Adenosine triphosphate shown). However, strain 4D9 grew very poorly with acetate (Fig. 4) ruling out this compound as a substrate. Second, it was analyzed which products are formed by chitinolytic enzymes of strain AH-1N by incubating embedded chitin in cell-free supernatant of this strain. During this incubation, chitin largely disappeared from the agarose beads, and HPLC analysis showed that up to 2 mM of GlcNAc accumulated (Fig. 3b). As strain 4D9 could grow with GlcNAc (Fig. 4), growth of strain 4D9 in the co-culture might be based on GlcNAc. To investigate this possibility, strain 4D9 was incubated with embedded chitin in cell-free supernatant of strain AH-1N. In these cultures, GlcNAc did not accumulate and strain 4D9 reached about 1400-fold higher CFU numbers in the suspended fraction (Fig. 5a) and about 64-fold higher CFU numbers in the biofilm fraction (Fig. 5b) compared to the control, in which strain 4D9 was incubated with embedded chitin in medium B.