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Appl Environ Microbiol. 1993 September; 59(9): 3091-3101

4-Methylumbelliferyl-ß-N-Acetylglucosaminide Hydrolysis by a High-Affinity Enzyme, a Putative Marker of Protozoan Bacterivory

Jaroslav Vrba^*, Karel imek, Jií Nedoma and Petr Hartman

Hydrobiological Institute, Czech Academy of Science, Na sádkách 7, 37005 eské Budjovice, Czech Republic

ABSTRACT

Hydrolysis of an artificial fluorogenic substrate, 4-methylumbelliferyl-ß-N-acetylglucosaminide, has been studied in a monoculture predator-prey system with either a flagellate (Bodo saltans) or a ciliate (Cyclidium sp.) fed upon pure bacterial culture (Aeromonas hydrophila or Alcaligenes xylosoxidans). Aeromonas hydrophila produced a low-affinity ß-N-acetylglucosaminidase-like enzyme (K_m, >>100 µmol liter^-1) but Alcaligenes xylosoxidans did not. Inoculation of both bacterial strains with bacterivorous protozoa induced the occurrence of another, high-affinity, ß-N-acetylglucosaminidase-like enzyme (K_m, <0.5 µmol liter^-1). The latter enzyme showed significant, close correlations with total grazing rates of both B. saltans (r² = 0.96) and Cyclidium sp. (r² = 0.89) estimated by using uptake of fluorescently labelled bacteria. Further significant correlations between several protozoan parameters and kinetic parameters of this enzyme suggest its likely protozoan origin. If both types of enzyme occurred together, they could be satisfactorily distinguished by using kinetic data analysis. Hence, measurements of ß-N-acetylglucosaminidase-like activities might be promising to use to improve estimations of protozoan bacterivory.

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FOOTNOTES

^* Corresponding author.

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Appl Environ Microbiol. 1993 September; 59(9): 3091-3101

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