Universität zu Köln

Sadler, Thomas ORCID: 0000-0002-8621-379X and von Elert, Eric ORCID: 0000-0001-7758-716X (2014). Dietary exposure of Daphnia to microcystins: No in vivo relevance of biotransformation. Aquat. Toxicol., 150. S. 73 - 83. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1879-1514

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Abstract

Anthropogenic nutrient input into lakes has contributed to the increased frequency of toxic cyanobacterial blooms. Daphnia populations have been shown to be locally adapted to toxic cyanobacteria and are able to suppress bloom formation; little is known about the physiology behind this phenomenon. Microcystin-LR (MCLR) is the most widespread cyanobacterial toxin, and, based on in vitro experiments, it is assumed that the enzyme glutathione-S-transferase (GST) might act as the first step of detoxification in Daphnia by conjugating MCLR with glutathione. In the present study Daphnia magna was fed a diet of 100% Microcystis aeruginosa PCC7806, a cyanobacterial strain that contains MCLR in high amounts (4.8-5.6 fg cell(-1)), in order to test for a possible conjugation of MCLR with GST in Daphnia in vivo. We used high-resolution LCMS to analyze incubation water, cyanobacterial cells and Daphnia tissue for the presence of MCLR conjugation products as well as unconjugated MCLR. Newly formed conjugation products were detected neither in Daphnia tissue nor in the incubation water. Moreover, the presence of Daphnia led to a decrease in unconjugated MCLR in the cyanobacterial cell fraction due to grazing, in comparison to a control without daphnids, which was well reflected by a similar increase of MCLR in the respective incubation water. As a consequence, the MCLR content did not change due to Daphnia presence within the entire experimental setup. In summary, MCLR ingestion by Daphnia led neither to the formation of conjugation products, nor to a decrease of unconjugated MCLR. GST-mediated conjugation thus seems to be of minor relevance for microcystin (MC) tolerance in Daphnia in vivo. This finding is supported by the fact that GST activity in Daphnia feeding on the MC-containing wildtype or a MC-free mutant of M. aeruginosa PCC7806 revealed an identical increase of specific activity in comparison to a cyanobacteria-free diet. Therefore, the frequently observed induction of GST activity upon exposure to toxic cyanobacteria is not a specific MC effect but a general cyanobacterial effect. This suggests that GST in Daphnia is involved in an oxidative stress response rather than in the specific detoxification of MCs. Furthermore, our results indicate the presence of an efficient transport mechanism which efficiently removes unconjugated MCLR from the Daphnia tissue. Further studies are needed to elucidate the nature of this transport mechanism. (C) 2014 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Sadler, Thomas UNSPECIFIED orcid.org/0000-0002-8621-379X UNSPECIFIED von Elert, Eric UNSPECIFIED orcid.org/0000-0001-7758-716X UNSPECIFIED
URN:	urn:nbn:de:hbz:38-438865
DOI:	10.1016/j.aquatox.2014.02.017
Journal or Publication Title:	Aquat. Toxicol.
Volume:	150
Page Range:	S. 73 - 83
Date:	2014
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1879-1514
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language CYANOBACTERIAL TOXINS; GLUTATHIONE TRANSFERASES; PROTEIN PHOSPHATASES; POPULATION-GROWTH; OXIDATIVE STRESS; AQUATIC ANIMALS; BIGHEAD CARP; LR; ZOOPLANKTON; AERUGINOSA Multiple languages Marine & Freshwater Biology; Toxicology Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/43886