Abstract
Laccases are oxidases that have numerous industrial and applications. They are well known as lignin degrading enzymes.
Majority of activity has been demonstrated in fungal species and their physiological roles is mainly the oxidation of phenolic subunit which leads to biodegradation.
In this study we evaluated the potential of fungal isolates from agro-wastes for laccase . Fungal cultures were screened for laccase production by plate test method using 2’ 2’ – azinobis-(-3-ethyl benzthiazoline -6- suphonate) (ABTS).
The isolates were further screened for laccase production in submerged culture using synthetic medium. Utilization of selected agro- wastes(sawdust, plantain and banana peels) residue for laccase production was evaluated.
Out of 12 fungal cultures tested, 5 cultures were found to be laccase positive and these were identified as Geotrichum sp, Cephalosporium sp, Trichoderma sp, Trametes sp and Fusarium sp.
These five fungal cultures were further used for quantitative screening with synthetic medium, Trichoderma sp gave the highest enzyme activity of 57.1U/l followed by Trametes sp with 51.99 U/l, Fusarium sp had 29.2 U/l.
Geotrichum sp and Cephalosporium sp recorded the lowest activities with 28.04 U/l and 9.72 U/l respectively all at the fourth day of incubation.
Trichoderma sp was selected as the most potent in producing enzyme and therefore used for further studies where the use of selected agro waste medium as different carbon sources, effect of different inoculum sizes, pH and use shaker was evaluated .
With respect to agro-wastes used sawdust medium gave the highest with 151.17 U/l followed by plantain peel medium with 62.49U/l, banana peel medium was the lowest with 54.94U/l.
Protein content obtained from sawdust medium was 45.8mg/ml, plantain peel medium had 29.2mg/ml while banana peel was the lowest with 16.8mg/ml all at the sixth day of the fermentation process.
The optimum pH for banana peel, plantain peel and sawdust was 5.94,5.83 and 5.95 respectively.
Introduction
Background Of Study
Fungi are vast group of eukaryotic organisms including yeast and molds that have a significant role in nature by breaking down organic material. These organisms are also producers of important antibodies, enzymes and food.
They are the only organisms that are able to completely mineralize lignocelluloses, the most abundant recalcitrant renewable material available in nature.
Fungi cells do so by producing several sets of enzymes for breaking down polysaccharides, celluloses and hemicelluloses as well as lignin, a natural aromatic polymer.
Ligninases or ligninolytic enzymes constitute a group of oxidoreductases that are specialized in polymerization as well as in the degradation of lignin (Thurston, 1994).
These enzymes are mostly produced by so called white-rot fungi and litter decomposing fungi (Assavanig et al., 1992).
Laccase is one of the three main ligninases and differs from the others in its ability to catalyze the oxidation of lignin components using molecular oxygen as the electron acceptor, which in turn is reduced to water (Kiiskinen and Saloheino, 2004).
In order to bring about the degradation of complex structures, laccases make use of small molecules as electron mediators both in nature and in the application developed by humans.
Laccase is among the oldest known enzymes, laccase activity was first discovered in 1883 in the sap of the Japanese lacquer tree Rhus vernicifera leading to its polymerization and the product is used commonly as Japanese lacquer varnish (Benfield et al., 1964).
Since then, the oxidative activity of laccase has been used in a number of industrial and environmental applications.
Although laccases originate from different sources like higher plant, bacteria, fungi and insect (Mayer and Staples, 2002) those from fungi origin are used in most of the application.
Laccases from a large number of fungi have been studied. These enzymes offer great variability in terms of induction mechanisms, degree of polymorphism, expression of different isoenzymes and physico–chemical and catalytic properties.
This variability determines the application for the isolated laccase and depends on whether the enzyme has a potential to oxidize a substrate or whether it is robust enough to be used in a certain application.
Hence, the search for fungal laccases with different properties and potential application is still on-going. It is expected that new isolated enzymes may catalyze old known process by a better way or may oxidize new substrates for novel application.
References
Abadulla, E., Tazanov, T., Costa, S., Robra, K., Cavaco-Paulo, A.,Gubitz, G.(2000).Decolorization and Detoxification of textile dyes with a Laccase from Trametes hirsula.Applied EnvironmentalMicrobiology66: 3357-3362.
Abyanova, A., Chulkin, A., Vavilova., E., Fedorova, T., Loginov, D., Koroleva, O.(2010).A heterologous production of Trametes hirsuta laccase in the fungus Penicillium Canescens.Applied Biochemistry Microbiology 46:313-317.
Acevedo, F., Pizzul, L., Castillo, M., Cueva, R., Diez, M.(2011).Degradation of polycyclic aromatic hydrocarbon by the Chilean white – rot fungus Anthracophyllum discolor. Journal Hazard Mater 185: 212 – 219.
Alcantra, A., De Fuente, I., Sinisterra, J.(1998).Rhizomucor miehei lipase as the catalyst in the resolution of chiral compounds. Chemistry Physics Lipids 93:168-187
Alper, N., Acar, J.(2004). Removal of phenolic compounds in pomegranate jucies using ultrafiltration and laccase-ultrafiltration combinating.Journal of Saudi Society of Agricultural Science 48:184 – 187.
Amitai, G., Adani, R., Sod-Moriah, G., Rabinovitz, I.,Vincze, A.,Leaader,H.(1998). Oxidative biodegradation of phosphorothiolates by fungal laccase FEBSLett 438:195- 200.
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