Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Laccase mediator system obtained from a marine spore exhibits decolorization potential in harsh environmental conditions Elaheh Asadi a , Ali Makhdoumi a,* , Ahmad Asoodeh b a Department of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran b Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran ARTICLE INFO Keywords: Decolorization Detoxification Laccase Laccase-mediator system Marine ABSTRACT Laccases play a significant role in remedying dye pollutants. Most of these enzymes are originated from ter- restrial fungi and bacteria, thus they are not proper to be used in the environments with neutral/alkaline pH, or they may require laborious extraction/purification steps. These limitations can be solved using marine spore laccases through high stability and easy to use application. In the current study, laccase activity of the marine spore -forming Bacillus sp. KC2 was measured according to the guaiacol and syringaldazine oxidation. Abiotic stresses like pH of 6, temperature of 37 °C and 0.3 mM CuSO 4 (in comparison with optimal sporulation con- ditions: pH of 8, temperature of 20 °C and 0.0 mM CuSO 4 ) enhanced laccase formation in sporal coat. Maximum activity of enzyme was observed at 50 °C and pH 7, which did not change in the alkaline pH and temperature range of 20–70 °C. Results indicated ions, inhibitors and solvent stability of the enzyme and its activity were stimulated by Co 2+ , Mn 2+ , PMSF, acetone, acetonitrile, ethanol, and methanol. The spore laccase could de- colorize synthetic dyes from various chemical groups including azo (acid orange, amaranth, trypan blue, congo red, and amido black), indigo (indigo carmine), thiazine (methylene blue, and toluidine blue), and triar- ylmethane (malachite green) with ABTS/syringaldazine mediators after 5 h. Degradation products were not toxic against Sorghum vulgare and Artemia salina model organisms. The enzyme mediator system showed high potentials for dye bioremediation over a wide range of harsh conditions. 1. Introduction Laccase (1,4-benzenediol: oxygen oxidoreductases) catalyzes en- vironmental friendly oxidation of different kinds of aromatic substrates coupled with direct reduction of molecular oxygen to water, without formation of intermediate hydrogen peroxide (Morozova et al., 2007a). The main substrates are phenolic and its relevant compounds; however, the substrate can be extended to non-phenolic compounds by inserting low molecular weight mediators (Laccase -Mediator System [LMS]) (Morozova et al., 2007b). The mediators are first oxidized by the en- zyme, after that they can oxidize (and degrade) non-phenolic com- pounds. It can be beneficial, when the redox potential of non-phenolic substances is higher than that enzyme, and the substrate cannot be oxidized directly. ABTS (2,2′-azino-bis(3-thylbenzothiazoline-6-sul- phonic acid)) is one of the most widely used mediator in the LMS (Christopher et al., 2014). Laccase and LMS can oxidize and remove various recalcitrant hazardous compounds such as Polycyclic Aromatic Hydrocarbons (PAH), Pentachlorophenols (PCP), Polychlorinated Bi- phenyls (PCB), and synthetic dyes (Chandra and Chowdhary, 2015). It is estimated that, almost 7 × 10 5 ˗ 1 × 10 8 tons dyes are produced annually all over the world and one-tenth of which may enter the en- vironment through industrial wastes (Chauhan et al., 2017). Dyes can adversely influence on the human and environmental health. They are toxic, mutagenic, carcinogenic, and allergen for human and other ani- mals. They reduce light penetration and photosynthesis in aqueous ecosystems, and they have negative aesthetic effects. Thus, efficient treatments to remove toxic dyes are extremely vital before discharging dyestuffs wastes into the environment (Pereira and Alves, 2012). Laccases are well determined in terrestrial organisms like higher plants, fungi, bacteria, and arthropods. Fungal laccases are good to be used in the industry, and they show higher enzymatic rate (due to higher redox potential). Isolation of bacterial laccase was first reported in 1993 (Givaudan et al., 1993) and after that, several bacterial taxa including Bacillus, Geobacillus, Streptomyces, Rhodococcus, Staphylo- coccus, Lysinibacillus, Aquisalibacillus, Pseudomonas, Enterobacter, Delfia, Proteobacterium and Alteromonas were reported as laccase producers (Chauhan et al., 2017). Applying most of these fungal and bacterial laccases for remediation processes is limited due to environmental https://doi.org/10.1016/j.ecoenv.2020.110184 Received 25 September 2019; Received in revised form 4 January 2020; Accepted 8 January 2020 * Corresponding author.Department of Biology, Faculty of Science, Ferdowsi University of Mashhad, P.O. Box: 91775-1436, Mashhad, Iran. E-mail address: a.makhdomi@um.ac.ir (A. Makhdoumi). Ecotoxicology and Environmental Safety 191 (2020) 110184 0147-6513/ © 2020 Elsevier Inc. All rights reserved. T