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AME 27:125-136 (2002)
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Abstract
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Microbial activity and bacterial community structure during degradation of microcystins
Kirsten Christoffersen1,*, Susanne Lyck1, Anne Winding2
1Freshwater Biological Laboratory, University of Copenhagen, 3400 Hillerød, Denmark
2Department of Microbial Ecology and Biotechnology, National Environmental Research Institute, 4000 Roskilde, Denmark
*E-mail: kchristoffersen@zi.ku.dk
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ABSTRACT: Degradation of realistic microcystin concentrations in lake water with indigenous bacteria was studied in laboratory and field experiments following inoculation with lysed toxic algal material containing microcystin primarily from
Microcystis sp. or purified commercial microcystin-LR to microcosms. It was hypothesised that the bacterial community from a lake with frequent occurrence of toxic cyanobacteria can degrade microcystin along with other organic compounds. The
initial dissolved microcystin concentrations ranged between 10 and 136 µg l-1 (microcystin-LR equivalents) in the laboratory experiment, using toxic natural algal material from 3 lakes and purified microcystin-LR, and between 2 and 54 µg
l-1 in the field experiment, using toxic natural algal material and material from a highly toxic culture. Lysed material from a non-toxic algal culture (Scenedesmus sp.) was included in the latter experiment to evaluate the effects of
organic lysates on bacterial proliferation in the absence of microcystin. An exponential decline of the dissolved toxins was observed in all cases with toxins present, and the degradation rates ranged between 0.5 and 1.0 d-1. No lag phases were
observed but slow initial degradation rates occurred in 2 out of 7 cases. Microcystin was almost eliminated from the water after around 8 d. Results from concomitant measurements of bacterial abundance and net production showed an elevated bacterial
activity within 1 to 2 d after the inoculation with algal lysates including microcystins, and this resulted in a net accumulation of bacterial cells. The heterotrophic nanoflagellates responded quickly to the bacterial growth and probably consumed a
considerable amount of the bacteria. The microbial activities returned to initial values within 5 to 6 d as the toxins and other dissolved organic substrates (measured as dissolved organic carbon [DOC]) were degraded. The degradation of DOC correlated
with the degradation of microcystin, which suggests that these processes are coupled. The diversities of the bacterial communities from the laboratory and field microcosm experiments were analysed by polymerase chain reaction-density gradient gel
electrophoresis (PCR-DGGE) of 16S rDNA, which showed that the indigenous bacterial community responded quickly to the addition of lysates. Our study confirms that bacteria can efficiently degrade microcystins in natural waters with previous cyanobacterial
histories and that the degradation process can run quickly and without lag phases.
KEY WORDS: Microcystins · Degradation rates · Bacteria · Community structure · 16S rDNA
Full text in pdf format
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Published in AME Vol.
27, No. 2
(2002) on March 15
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2002
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