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Extracellular, low‐affinity β‐ N ‐acetylglucosaminidases linked to the dynamics of diatoms and crustaceans in freshwater systems of different trophic degree
Author(s) -
Vrba Jaroslav,
KofroňováBobková Jitka,
Pernthaler Jakob,
Simek Karel,
Macek Miroslav,
Psenner Roland
Publication year - 1997
Publication title -
internationale revue der gesamten hydrobiologie und hydrographie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.524
H-Index - 52
eISSN - 1522-2632
pISSN - 0020-9309
DOI - 10.1002/iroh.19970820213
Subject(s) - epilimnion , crustacean , diatom , biology , extracellular , algae , eutrophication , trophic level , phytoplankton , ecology , nutrient , biochemistry , hypolimnion
Extracellular hydrolysis of 4‐methylumbelliferyl β‐ N ‐acetylglucosaminide was measured in the oligomesotrophic Piburger See and the eutrophic Římov reservoir during spring and summer phytoplankton blooms, respectively. Total enzymatic activity (TEA) ranged between 0.2 and 19.1 nmol 1 −1 h −1 in the reservoir and between 0.8 and 12.4 nmol 1 −1 h −1 in the lake. High‐affinity ( K m < 1 μmol 1 −1 ) and lowaffinity ( K m > 100 μmol 1 −1 ) enzymes were kinetically identifiable in most samples from both localities. The low‐affinity enzyme activity (LEA) usually accounted for >60% (mean: 80%) of TEA. LEA and diatom biomass significantly correlated over time in the reservoir epilimnion ( r s = 0.578) and in the lake metalimnion ( r s = 0.862). As diatoms possess chitin and take up its monomer, N ‐acetylglucosamine, two explanations of the observed relationships are suggested: extracellular β‐ N ‐acetylglucosaminidase activity partly originates either from ectoenzymes of chitinolytic bacteria attached to diatom cells or from ectoenzymes of diatoms, enabling them to take up N ‐acetylglucosamine from ambient amino sugars instead of synthesizing it de novo. A significant positive correlation of LEA with crustacean abundance was found in the lake epilimnion ( r s = 0.850), apparently reflecting the growing spring populations of frequently moulting juvenile crustaceans. A possible contribution of chitinolytic bacteria, accompanying the crustacean populations, to LEA is discussed.

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