Screening of newly isolated marine-derived fungi for their laccase production and decolorization of different dye types

Highlights

• Marine derived fungi were isolated using the new isolation process.

• Decolorization of six different dyes was achieved over 50% by Alternaria sp. D21.

• Laccase from marine derived fungi is important in environmental pollution removal.

• The findings of the study are promising for the prevention of marine pollution.

Abstract

Six marine-derived fungi (Alternaria sp. D11, Alternaria sp. D21, Cadophora sp. D43, Cadophora luteo-olivacea D51, Phoma sp. K2BR, Phoma sp. K21) were isolated from the Çakalburnu Lagoon, Izmir Bay, Aegean Sea in Turkey. An effective method has been developed for marine-derived fungi isolation and laccase production of the fungi has been studied. This method consisted of immersing a sterile solid substrate containing lignin into the aquatic system under aseptic conditions and removing at the end of 10 days, isolation for laccase producing fungi of marine origin. The decolorization potential of the isolate Alternaria sp. D21 with the highest laccase activity was investigated for dyes containing azo, anthraquinone, triarylmethane and heterocyclic chemical classes. The decolorization rates were determined as 98% for Methyl orange, 93% for Acid green 3, 78% for Methylene blue, 71% for Remazol Brilliant Blue, 58% for Crystal violet, and 53% for Congo red after 144 h at 100 mg/L concentration of dyes. The ability of the marine-derived fungi to remove dyes of different chemical classes is also promising for waste containing mixtures of various pollutants.

Introduction

Pollution of aquatic environments is a big problem today and continues to increase. The wastes of many industries are dumped into marine and freshwater systems. One of these industries is textile industries that produce intensive dye wastes (Rao et al., 2010). Most of the annual synthetic dye production is made up of azo, anthroquinone, triphenylmethane and heterocyclic polymeric dyes. In addition, anthraquinone dyes constitute the second most used dye group in the world. Sectors in which they are used; paper and cellulose industry, textile and paint industries (Vala and Dave, 2017, Rao et al., 2010).

After the painting process, 10%–15% of the unused dyes are added to the water systems as waste. Dyes released into aquatic systems make it difficult for sunlight to reach the lower layers, thus causing reduced primary production and lower efficiency. Most synthetic dyes are toxic, mutagenic and carcinogenic. Most physico-chemical methods used conventionally for color removal have one or more limitations. These limitations include high cost, many chemical compounds, and limited applicability. These reasons led researchers and scientists to find biological and environmentally friendly methods (Vala and Dave, 2017).

The fungi have strong extracellular enzyme production capacity and most studies have been focused on them for finding environmentally friendly wates removal methods. There are many studies on fungal enzymes in terrestrial systems. However, there is not enough data on aquatic systems (Richards et al., 2012, Ben Ali et al., 2020). In marine environments, fungi are involved in the degradation of lignocellulosic materials. Lignolytic fungi of marine origin, including Basidiomycetes, Ascomycetes and Deuteromycetes, have spores with different characteristics than their terrestrial counterparts. The expression “grows only under sea conditions and creates spores” describes obligate marine fungi (Kohlmeyer and Kohlmeyer, 1979). “Facultative marine fungi” is a definition used for terrestrial-based fungi, which are capable of growth and spore formation in marine environments. The fungi perform degradation of lignin by extracellular enzymes such as laccase, manganese peroxidase and lignin peroxidase. These enzymes have also been reported to be effective on environmental contaminants such as dye and textile wastes, agricultural chemicals, and pulp mills wastes (Kiiskinen et al., 2004, Mtui and Nakamura, 2004).

Laccases (EC 1.10.3.2) are a multigenic family of multicopper oxidase found in bacteria, fungi and plants (Reiss et al., 2013, Ben Ali et al., 2020). Fungal laccases are dimeric or tetrameric glycoproteins with four copper atoms in the catalytic domain per monomer. Laccases have a wide range of substrates that can serve industrial purposes and biological waste disposal processes. An important feature that distinguishes laccases from other lignolytic enzymes is that they do not need the addition of cofactors for their activity. The fact that these enzymes are usually secreted naturally and are highly stable outside the cell provide them an important advantage in environmental applications (Yoshitake et al., 1993, Ben Ali et al., 2020).

The production of laccases from new sources is very important industrially and one of these sources could be the marine environments. The fungi from marine sources that colonize mangrove leaves, ramages, weeds and pieces of wood can produce lignin degrading enzymes (Pointing and Hyde, 2000, Bucher et al., 2004). The fungi in marine systems are expected to adapt to growth under saline (10–34 ppt salinity) and alkaline conditions because the pH of the seawater is in the range of 7.5–8.2. The textile, paper, cellulose factories and molasses-using factories are industries that produce lignin-derived compounds as waste. Laccase producing marine-derived fungi are used for bioremediation applications of these wastes. The content of these wastes is alkaline and highly salty. The marine-derived fungi have adapted to salty and alkaline conditions due to their habitats. For this reason, the potential of facultative or obligate marine-origin fungi of these waste removal studies is high (Raghukumar et al., 2008).

In this study, a new isolation method of laccase producing fungi from two different aquatic environments such as lagoon and marine water was applied. Then, laccase production in saline and alkaline conditions by marine origin fungi, which are not frequently detected in these environments; was investigated by different media, indicator compounds and decolorization of Remazol Brilliant Blue R dye. In addition, decolorization rates of dyes belonging to different chemical classes were examined without using mediators.