Oxidative stress and toxicology of Cu2+ based on surface areas in mixed cultures of green alga and cyanobacteria: The pivotal role of H2O2

Author(s)

Gallo, Michelle ^[1] ; Morse, David ^[2] ; Hollnagel, Heloisa C. ^[3] ; Barros, Marcelo P. ^[1]

Affiliation

^[1] Cruzeiro do Sul Univ, Program Hlth Sci, Rua Galvao Bueno 868, BR-01506000 Sao Paulo, SP - Brazil

^[2] Univ Montreal, Inst Rech Biol Vegetale, Dept Sci Biol, Montreal, PQ H1X 2B2 - Canada

^[3] Univ Fed Sao Paulo UNIFESP, Campus Osasco, BR-06110295 Osasco, SP - Brazil

• Document type: Journal article
• Source: AQUATIC TOXICOLOGY; v. 222, MAY 2020.
• Web of Science Citations: 0

Abstract

The toxicity of heavy metals in algal monocultures is well studied and is mediated by reactive oxygen and nitrogen species (ROS/RNS). However, little is known about the toxicity of heavy metals and the mechanisms involved in mixed cultures. Here we examine the oxidative stress and toxic effects of Cu2+ on the green alga Dunaliella salina (DS) and the cyanobacteria Synecochoccus elongatus (SE) in both mono- and mixed cultures. We find that both species benefit in mixed cultures and acquire higher resistance to Cu2+ toxicity, with a particularly marked effect on SE. DS has a larger surface area than SE, so increases in the number of DS cells compared to SE diminishes the proportion of SE surface area exposed to Cu2+, and contributes to increasing cyanobacterial resistance in mixed cultures. However, these mixed cultures also display as an unexpected property an increased resistance of DS in mixed cultures. SE and DS cells showed significant differences on the kinetics of H2O2 production and antioxidant capacities. The integrated (overall) redox response of mixed cultures, in terms of total amount of H2O2 produced, was proportional to the total surface area of algal species exposed to Cu2+, independent of algal composition in mixed systems. However, mixed cultures display emergent properties, as the time course of H2O2 accumulation is not a simple function of the composition of the mixed cultures. Emergent properties are also observed in the speed of membrane lipid oxidation by the two species, as measured using mixed cultures in which only one of the two species is labeled using the membrane oxidation indicator C-11-BODIPY581/591. We suggest that, in addition to H2O2, other redox signals (e.g. NO center dot) and allelochemicals (auxins, cytokinins, etc.) may be used to construct a complex inter-species communication network. This could allow mixed algal systems, whatever their composition, to integrate their cellular responses and perform as a coherent unit against toxic Cu2+ ions. (AU)

• FAPESP's process: 17/06032-2 - Biochemical, physiological and transcriptomic strategies to study the relationship between carotenoids, oxidative stress and Citrus fruit quality
• Grantee: Marcelo Paes de Barros
• Support Opportunities: Scholarships abroad - Research