Microbial activity and bacterial community structure during degradation of microcystins

TY - JOUR

T1 - Microbial activity and bacterial community structure during degradation of microcystins

AU - Christoffersen, K.

AU - Lyck, Susanne

AU - Winding, A.

PY - 2002

Y1 - 2002

N2 - 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 mug 1(-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 mug 1(-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 phase

AB - 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 mug 1(-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 mug 1(-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 phase

KW - Faculty of Science

KW - Keywords: microcystins; degradation rates; bacteria; community structure; 16S rDNA KeyWords Plus: CYANOBACTERIAL HEPATOTOXINS; ACTIVATED CARBON; LR; LAKE; WATER; ADSORPTION; BIODEGRADATION; HEPTAPEPTIDES; DESTRUCTION; BLOOMS

M3 - Journal article

SN - 0948-3055

VL - 27

SP - 125

EP - 136

JO - Aquatic Microbial Ecology

JF - Aquatic Microbial Ecology

IS - 2

ER -