جداسازي و شناسايي باكتري‌هاي تخريب‌كننده‌ي ليگنين و ارزيابي عملكرد آن‌ها در تخريب ليگنين و زيست‌توده ليگنوسلولزي

Isolation an‎d identification of lignin-degrading bacteria an‎d assessment of their performance in degrading lignin an‎d lignocellulosic biomass

زيست فناوري

Lignin, a heteropolymer in the lignocellulose structure, plays a key role in the strength an‎d stability of plants. This heteropolymer is often considered a "nuisance" in industries like pulp an‎d paper mills because various physical an‎d chemical methods are used to separate cellulose an‎d hemicellulose from it. Unfortunately, the separated lignin is usually not properly disposed of an‎d is therefore improperly released into the environment. Using biological methods for lignin degradation offers significant advantages. For example, these methods are not only cost-effective but can also break down lignin into simpler compounds with higher added value. Consequently, the resulting compounds can be used as raw materials in other industries, preventing the improper release of lignin into the environment. The objective of this research was to search for an‎d isolate bacteria with lignin-degrading enzymes. Furthermore, experiments were conducted on the bacterium Deinococcus radiodurans to eva‎luate its potential in this area. Three bacteria, including Acinetobacter olivorans (SFD1), Enterobacter cloacae (SFD2), an‎d Escherichia coli (SFD3), were isolated an‎d registered with the accession numbers PP767398, PP951854, an‎d PQ368848 on the NCBI website, respectively. The activity levels of manganese peroxidase (MnP), lignin peroxidase (LiP), an‎d laccase (Lac) enzymes, which are involved in the lignin degradation process, were measured in these three isolates by the oxidation of substrates such as 2,6-dimethoxyphenol, veratryl alcohol, an‎d 3-ethylbenzothiazoline-6-sulfonic acid (ABTS), respectively. The results showed that the highest activities for lignin peroxidase, manganese peroxidase, an‎d laccase were recorded for Deinococcus radiodurans (615 units), Acinetobacter olivorans (130 units), an‎d Enterobacter cloacae (4120 units), respectively. Additionally, the gene encoding the multicopper oxidase (CueO) enzyme, which is similar to laccase, was identified in the Escherichia coli isolate using a set of designed primers, which justifies the ability of this isolated strain to degrade lignin. The released low-molecular-weight compounds were eva‎luated an‎d identified using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Fourier-Transform Infrared Spectroscopy (FT-IR) analysis also showed changes in the chemical structure an‎d the production of alcohol, phenolic (OH-), an‎d aromatic (C=C) compounds by the isolates. The obtained results indicated that the isolated bacteria an‎d the Deinococcus radiodurans strain efficiently degrade lignin, with the highest degradation (66.4%) observed for the Enterobacter cloacae isolate. Notably, this research for the first time isolated an‎d introduced a naturally-occurring Escherichia coli strain with lignin-degrading ability (44%). Given the importance of Escherichia coli as a host strain in industrial bioprocesses, this isolate holds high potential for use in biorefineries for lignin valorization an‎d for the removal of lignin from industrial effluents.

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