Effect of cadmium (Cd2+) on the metabolome and physiology of Brazilian red macroalgae

Author(s)

Luiza de Araújo Motta

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2021-10-21

Examining board members

Pio Colepicolo; Carlos Takeshi Hotta; Claudio Martin Pereira de Pereira; Maurício Yonamine

• Advisor: Pio Colepicolo

Abstract

Algae are fundamental organisms for the evolution of terrestrial life, mainly because they are important producers of O2 and organic matter. These organisms are responsible for half of the total global photosynthetic activity. Furthermore, algae play an important role in energy transformations, in nutrient recycling and represent the basis of the food chain in aquatic environments. Because of these and others ecological functions performed by marine algae, these organisms have been studied for their capacity of being used in biomonitoring and bioremediation of the environment, which is attributable to a great application of environmental conservation. The effects of non-essential metals in aquatic environments, including cadmium, are already known and are mainly related to the imbalance of the cellular redox system. Metabolomic analysis has become an important tool for environmental conservation, with a high technical sensitivity its guarantee an early and efficient toxicological diagnosis. The main objective of this study was to better understand the metabolic effects of Cd2+ exposure on the Brazilian red algae selected with a greater resistance. For this propose, the macroalgae Gracilaria domingensis, Crassyphycus caudatus and Hypnea spinella were grown in natural seawater and exposed to increasing concentrations of cadmium (Cd2+), the daily growth rate was evaluated for each specie. From these growth curves the specie with greater resistance was selected and another toxicological test designed to determine the IC50 of Cd2+ exposure. From these results it was evaluated the effect of Cd2+ exposure in the metabolism of the selected macroalgae, including concentrations legally permitted by Conama for marine environments. The metabolism was evaluated specific for the photosynthesis (fluorescence measurements) and with general metabolomic analyses (Gas chromatographymass spectrometry- GC-MS). The metabolomic data was normalized and scaled to be compared in multivariate statistical tests (PCA and OPLS-DA). The results of the toxicological assays indicated C. caudatus as the specie with the greater resistance for Cd2+ exposure, with the IC50 of 3 mg/L that can be observed with 48h of exposure. Photosynthetic measurements showed changes in some of the parametersanalyzed, including for those concentration legally allowed in the national environment. In the metabolomic analysis, several specific changes were detected, however, the total metabolic profile was just considered statistically different from that observed in the control group, only in the highest concentration of Cd2+ evaluated, its IC50 (3 mg/L). The differences observed showed significatively changes in 6 metabolic pathways, where the main results are related to a greater photorespiration activity, which we suggested as an attempt of the macroalgae in maintaining the carbon flow affected by the reduction of photosynthetic activity. Important cellular antioxidant production pathways were also more active in the presence of the metal, as a response of defense against oxidative damage caused by the metal. In addition, more activity of glycerol metabolism was detected, suggested as a cellular need for glycerophospholipid bioavailability for the isolation of the metal ions absorbed in vesicles and/or an increase in degradation of stored triglycerides used as source of energy impaired by oxidative damage. The understanding of metabolic changes triggered by Cd2+ with the detection of defense mechanisms performed by the macroalgae, show an important diagnosis of the possible damage caused by pollution in the marine environment. (AU)

• FAPESP's process: 18/10216-4 - Analysis of the biochemical effects of Brazilians red macroalgae species exposed to cadmium
• Grantee: Luiza de Araujo Motta
• Support Opportunities: Scholarships in Brazil - Master