Name: FERNANDA BRÊDA ALVES
Type: PhD thesis
Publication date: 06/09/2019
Advisor:

Name	Role
Mathias Ahii Chia	Co-advisor *
Valéria de Oliveira Fernandes	Advisor *

Examining board:

Name	Role
Camilla Rozindo Dias Milanez	Internal Alternate *
Karoline Magalhães Ferreira Lubiana	External Examiner *
Maria do Carmo Pimentel Batitucci	Internal Examiner *
Mathias Ahii Chia	Co advisor *
Micheline Kézia Cordeiro de Araújo	External Examiner *
Paola Alfonsa Vieira Lo Monaco	External Alternate *
Valéria de Oliveira Fernandes	Advisor *
Viviana Borges Corte	Internal Examiner *

Summary: ABSTRACT
Cyanobacteria are photosynthetic organisms that make up the base of the aquatic food chain. Changes in the physical and chemical conditions of aquatic environments, such as increased nutrients and the presence of agrochemicals, alter the structure and dynamics of phytoplankton. Herbicides contaminate the aquatic environment through surface runoff at high concentrations; these compounds cause oxidative stress, interfere with the normal functioning of enzymes and alter the metabolic profile of microalgae and cyanobacteria. The present study investigated the toxicological and physiological effects of clethodim herbicide, as well as nitrogen variation in allelopathic interactions and toxin production by Microcystis aeruginosa BCCUSP232 and Raphidiopsis raciborskii ITEPA1. Effective concentrations (EC50) after 96 hours of exposure of both strains to clethodim were 192.98 mg / L and 168.73 mg / L for R. raciborskii and M. aeruginosa, respectively. The presence of clethodim significantly increased the total microcystin content of M. aeruginosa. In mixed cultivation M. aeruginosa, presented higher cell density when exposed to clethodim, while the highest density of R. raciborskii was observed when exposed to clethodim with limited nitrogen addition. The total content of microcystins (MCs) in mixed culture was 68% higher in nitrogen-enriched cultures than control. A similar increase in MC content was recorded in M. aeruginosa monocultures treated with R. raciborskii exudate. Total saxitoxin concentration was higher in R. raciborskii mixed cultures simultaneously exposed to high nitrogen and clethodim. The intracellular H2O2 content of M. aeruginosa cultures decreased while in R. raciborskii cultures increased during exposure to nitrogen and clethodim. GST activities in cultures of both strains were higher in the presence of clethodim. Our study revealed that nitrogen enrichment and low clethodim concentration could lead to excessive proliferation of M. aeruginosa and R. raciborskii and cyanotoxin production in aquatic environments.

Keyword: Cyanobacteria; Cyanotoxins; Toxicity; Allelopathy; Agrochemicals