, 2008). Chitin degradation via released chitinases has been well described for marine bacteria of the genera Vibrio and Pseudoalteromonas (Keyhani & Roseman, 1999; Baty et al., 2000; Meibom et al., 2004) and for freshwater bacteria of the genus Aeromonas (Janda, 1985; von Graevenitz, 1987; Lan et al., 2008). On the contrary, chitin degradation via cell-associated chitinases is largely unexplored. It has been described that many chitinolytic bacteria of the Cytophaga/Flavobacterium group of Ruxolitinib the Bacteroidetes, which are abundant inhabitants of marine and freshwater environments and contribute significantly to polymer

degradation in the open water (Cottrell & Kirchman, 2000; Kirchman, 2002; Lemarchand et al., 2006; Alonso et al., 2007; Beier & Bertilsson, 2011), do not release chitinases (Sundarraj & Bhat, 1972; Gooday, 1990). Recent genome analyses of several Bacteroidetes such as Flavobacterium johnsoniae suggest that chitin degradation in this group of bacteria proceeds via surface-bound chitinolytic enzymes that are very similar MAPK inhibitor to the well-described starch utilization system (sus) of Bacteroides thetaiotaomicron (Bauer et al., 2006; Xie et al., 2007; Martens et al., 2009; McBride et al., 2009).

The goal of our study was to investigate the interactions of bacteria with contrasting mechanisms for chitin degradation to identify the strategies they apply for overcoming their respective disadvantages. As this is difficult to study within natural communities, we set up a reductionistic laboratory model system with a defined co-culture

of aquatic bacteria, Aeromonas hydrophila strain AH-1N and Flavobacterium sp. strain 4D9. Previously, we reported that strains of Aeromonas and of the Cytophaga/Flavobacterium group were dominant in the same enrichment cultures, in which the microbial communities of the littoral zone of the oligotrophic PRKACG Lake Constance had been supplied with artificial organic particles as substrate (Styp von Rekowski et al., 2008). Thus, members of these bacterial groups coexist in the same environment. As described above for polymers in general, naturally occurring chitin is usually linked to other organic components such as proteins or glucans (Gooday, 1990). To account for this in our study, we embedded chitin into agarose beads. Aeromonas hydrophila strain AH-1N (Lynch et al., 2002) and Flavobacterium sp. strain 4D9, a Lake Constance isolate formerly called Cytophaga sp. strain 4D9 (Styp von Rekowski et al., 2008; GenBank accession number EF395377), were cultivated in the mineral medium B (Jagmann et al., 2010). When acetate (5 mM) and tryptone (0.1%) were used as carbon and energy sources, 5 mM NH4Cl was present in the medium. When suspended chitin [0.5% (w/v)], embedded chitin (two chitin-containing agarose beads per test tube), or GlcNAc (5 mM) served as carbon, energy, and nitrogen source, ammonium was omitted from the medium. Both strains were maintained on solid (1.