title: Bacterial chitin hydrolysis in two lakes with contrasting trophic statuses.
abstract: Chitin, which is a biopolymer of the amino sugar glucosamine (GlcN), is highly abundant in aquatic ecosystems, and its degradation is assigned a key role in the recycling of carbon and nitrogen. In order to study the significance of chitin decomposition in two temperate freshwater lakes with contrasting trophic and redox conditions, we measured the turnover rate of the chitin analog methylumbelliferyl-N,N'-diacetylchitobioside (MUF-DC) and the presence of chitinase (chiA) genes in zooplankton, water, and sediment samples. In contrast to the eutrophic and partially anoxic lake, chiA gene fragments were detectable throughout the oligotrophic water column and chiA copy numbers per ml of water were up to 15 times higher than in the eutrophic waters. For both lakes, the highest chiA abundance was found in the euphotic zone--the main habitat of zooplankton, but also the site of production of easily degradable algal chitin. The bulk of chitinase activity was measured in zooplankton samples and the sediments, where recalcitrant chitin is deposited. Both, chiA abundance and chitinase activity correlated well with organic carbon, nitrogen, and concentrations of particulate GlcN. Our findings show that chitin, although its overall contribution to the total organic carbon is small (~0.01 to 0.1%), constitutes an important microbial growth substrate in these temperate freshwater lakes, particularly where other easily degradable carbon sources are scarce.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters-Research and Management, Kastanienbaum, Switzerland. Krista.Koellner@eawag.ch
authors.forename: Krista E
authors.initials: KE
authors.lastname: Köllner
authors.forename: Dörte
authors.initials: D
authors.lastname: Carstens
authors.forename: Esther
authors.initials: E
authors.lastname: Keller
authors.forename: Francisco
authors.initials: F
authors.lastname: Vazquez
authors.forename: Carsten J
authors.initials: CJ
authors.lastname: Schubert
authors.forename: Josef
authors.initials: J
authors.lastname: Zeyer
authors.forename: Helmut
authors.initials: H
authors.lastname: Bürgmann
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism*; D002686:Chitin / Q000378:metabolism*; D002688:Chitinases / Q000235:genetics / Q000378:metabolism; D005618:Fresh Water / Q000382:microbiology*; D019015:Geologic Sediments / Q000382:microbiology; D006868:Hydrolysis; D006923:Hymecromone / Q000031:analogs & derivatives / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism; D015048:Zooplankton / Q000382:microbiology
chemical_list: D009844:Oligosaccharides; D002686:Chitin; D006923:Hymecromone; C033855:4-methylumbelliferyl-N,N-diacetylchitobioside; D002688:Chitinases
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