Laccase-like enzyme activities from chlorophycean green algae with potential for bioconversion of phenolic pollutants

Abstract

In order to explore the abundance and potential environmental functions of green algal laccases, we screened various algae for extracellular laccase-like activities, characterized basic features of these activities in selected species and exemplarily studied the transformation of environmental pollutants and complex natural compounds by the laccase of Tetracystis aeria. Oxidation of the classical laccase substrate ABTS was found to be widespread in chlorophycean algae. The oxidation activity detected in members of the 'Scenedesmus' clade was caused by an unknown thermostable low-molecular-mass compound. In contrast, species of the Moewusinia, including Chlamydomonas moewusii and T. aeria, excreted putative 'true' laccases. Phenolic substrates were oxidized by these enzymes optimally at neutral to alkaline pH. The Tetracystis laccase efficiently transformed bisphenol A, 17α-ethinylestradiol, nonylphenol and triclosan in the presence of ABTS as redox mediator, while anthracene, veratrylalcohol and adlerol were not attacked. Lignosulfonate and humic acid underwent slight (de)polymerization reactions in the presence of the laccase and mediator(s), probably involving the oxidation of phenolic constituents. Possible natural functions of the enzymes, such as the synthesis of complex polymers or detoxification processes, may assist the survival of the algae in adverse environments. In contaminated surface waters, laccase-producing green algae might contribute to the environmental breakdown of phenolic pollutants.

Phenoloxidases in Plants—How Structural Diversity Enables Functional Specificity

“…There are conflicting reports on exact appearance of LACs in plants. Green unicellular algae, such as Volvox carteri and Chlamydomonas reinhardtii, were suggested to have genes encoding for LACs Zhao et al, 2013) although no LAC enzymatic activities had been detected in these species (Otto et al, 2015).…”

Effects of sodium sulfate on the freshwater microalgaChlamydomonas moewusii: implications for the optimization of algal culture media

“…Kinetic equations, which describe the growth in relation to a nutrient, are important in understanding many phenomena in biotechnological and ecological processes. C. moewusii is a microalga widely used as a model organism for many studies in biology, for example, toxicological studies (Su arez et al 2010, Mera et al 2014, flagellar structure (Jones and Lewin 1960), studies with chloroplasts (Richard et al 1994), biosynthesis of metabolites , biotransformation (Otto et al 2015), and genetic studies (Bussieres et al 1996).…”

Extracellular polymeric substances with high radical scavenging ability produced in outdoor cultivation of the thermotolerant chlorophyte Graesiella sp.

“…Some extracellular enzymes such as protease (Kellam and Walker 1987), phenol oxidase (Otto and Schlosser 2014), and laccase like enzyme (Otto et al 2015) have been identified in some Chlorophyta EPSs. Other exoenzymes were also found in several microalga strains (Liu et al 2016).…”