SHARLEEN LIVINA ISAAC
UNIVERSITI PUTRA MALAYSIA (UPM)
Why bacterial laccases?
Now, imagine going to the river for fishing. Industrial wastes are found lying around. Then, adding to the misery, once a favorite spot to unwind is now stinking of dead organisms and effluents. Such a horrible sight it must be. Sadly, this is the reality these days. However, what if there is an alternative? The alternative to revitalize the environment again?
LACCASES! Mother Nature’s very own Batman, Superman, and Avengers combined will revive the deteriorating environment. They can survive in extreme conditions regardless of pH, temperature, organic solvents, and salt concentrations, besides possessing a high redox potential. Most importantly, with their superpowers, they can degrade wastes from industrial processes.
Laccase, an oxidoreductase enzyme, attacks only phenolic compounds. It was first discovered from a Japanese lacquer tree, Rhus verniczfera, thus coining the term ‘laccase’. Almost a century later, the isolation of the first bacterial laccase from Azospirillum lipoferum marked the beginning of a much robust enzyme for its use in industrial processes and environmental revitalization.
Typically, laccase from the multi-copper oxidase origin possesses four copper atoms involved in converting an oxygen molecule to water molecules on additional reduction of four electrons without releasing any reactive oxygen species. Hailing from the cupredoxin family, the four copper atoms unique to each other in terms of the oxidation state consists of two beta-sheets, taking the shape of a Greek key beta-barrel. In addition, one of the four copper atoms gives laccase its blue coloration, while laccases lacking that particular copper atom are typically known to exhibit yellow or white coloration.
Interestingly, phylogenetic studies have attested that this enzyme has evolved through time in organisms because of gene duplication but executed similar biochemical activity.
Being widely distributed and studied in fungi and plants, bacterial laccases confined either extracellularly or intracellularly exhibit better features than their counterparts from the Eukaryota domain. Although fungal laccases, unlike bacterial laccases, possess a higher redox potential, numerous studies have manifested the setbacks of fungal laccases and regarded them futile to some extent due to their longer fermentation rate, low yield, and their ability to grow only under acidic conditions, deterring their applications in industry as most operations require them to work in extreme conditions. Conversely, laccases of bacterial origin are more tolerant to extreme temperatures, pH and easily reproducible in a greater yield, apt for industrial applications.
Their applications include:
1. Delignification of pulp and paper: Common approaches for pulp bleaching release halogenic organic compounds through the utilization of chlorine. Thermus sp. 2.9 and Amycolatopsis sp. 75iv3 laccases were highly stable in the delignification of pulp and paper.
2. Construction of biosensors: Electrochemical biosensors using laccases are commonly utilized due to their high reactivity and selectivity. The biosensors have also been found effective in detecting phenolic compounds in wine, pharmaceutical, and wastewater samples.
3. Degradation of pollutants: Laccases have also aided in bioremediation. Many studies have shown that laccase from Bacillus sp. could degrade chlorophenols – used in pesticides, herbicides, antiseptics, and disinfectants, and bisphenols – used in plastic-making.
4. Decolorization of textile dyes: Textile effluents often involves a high concentration of chloride ions. However, Pantoea anantis Sd-1 and Bacillus sp. CF96 laccase isolated from a termite’s digestive system is among the few bacterial laccases that exhibited high thermal stability and persisted through high salt concentration in textile dye decolorization.
Studies on bacterial laccases are still scarce. However, their biotechnological applications remain diverse. Just as the worldwide epiphany that the environment might serve as thresholds for various compounds of furtive but forbidding chemicals and waste released into the surroundings, bacterial laccase may be the only saving grace in alleviating the environment. Industrial wastes being a constant threat to the pristine waters and nature as the overwhelming improper waste management incessantly occurring, laccases will be the turn of the tide. On top of everything, it is a win-win situation. The industry will still be able to make profits with the inexpensive and bountiful production of bacterial laccase. Nature, on the other hand, will be preserved of its serenity. By and large, the right strategies implemented through protein engineering, synthetic biology, and genetic engineering in revamping the enzyme kinetics and activity undoubtedly can vanquish even more severe environmental issues.