Copper ion-stimulated McoA-laccase production and enzyme characterization in Proteus hauseri ZMd44

Production optimization, characterization, and application of a novel thermo- and pH-stable laccase from Bacillus drentensis 2E for bioremediation of industrial dyes

Environmental pollution driven by rapid industrialization and urbanization, has become serious concern due to adverse health effects. Among various bioremediation strategies, laccase, an oxidoreductase enzyme with wide substrate range and high redox-potential (0.4-0.8 V) has garnered significant attention due to its ability to oxidize various organic pollutants into non-toxic products. However, its practical application is often limited due to susceptibility to extreme pH and inhibitory compounds present in wastewater. To overcome this challenge, bacterial laccase, also known as versatile laccases, offer superior stability under harsh environmental conditions making them ideal for bioremediation. Furthermore, isolating native bacterium from contaminated sites enhances their potential, as these organisms are naturally adapted to pollutant-rich environments with intrinsic degradation ability. In this study, Bacillus drentensis 2E was isolated from dye-effluent release site. Laccase production was systematically optimized by One-Factor-at-a-Time, Plackett-Burman Design, and Central Composite Design, yielding a 2.45-fold increase in activity compared to unoptimized condition. Optimized media composition is as follows (g/L): KNO3-5.034,Glucose-3, KH2PO4-0.3,MgSO4-0.3, NaCl-0.55, CaCl2-0.55, CuSO4-0.178 mM, inoculum volume-3.54 %. The enzyme was further characterized for kinetic properties against ABTS, guaiacol and syringaldazine. It demonstrated exceptional stability across a wide temperature (20 ± 1 °C-70 ± 1 °C) and pH range (3.0 ± 0.01-8.0 ± 0.01) with heavy metal tolerance to Ca2+, Mn2+, Mg2+,Zn2+,Cu2+,Co2+,Ni2+. Also, BDLaccase effectively degraded Acid Red-27 (99.76 ± 2.27 %) and Direct Blue-6 (67.43 ± 2.31 %) within 5 h, as confirmed using UV-Vis spectroscopy, FT-IR, and LC-MS. These findings suggests that, BDLaccase is a robust biocatalyst for bioremediation especially in treatment of dyes due to its broad stability and efficiency.

Evaluating lignin degradation under limited oxygen conditions by bacterial isolates from forest soil

Lignin, a heterogeneous aromatic polymer present in plant biomass, is intertwined with cellulose and hemicellulose fibrils, posing challenges to its effective utilization due to its phenolic nature and recalcitrance to degradation. In this study, three lignin utilizing bacteria, Klebsiella sp. LEA1, Pseudomonas sp. LEA2, and Burkholderia sp. LEA3, were isolated from deciduous forest soil samples in Nan province, Thailand. These isolates were capable of growing on alkali lignin and various lignin-associated monomers at 40 °C under microaerobic conditions. The presence of Cu2+ significantly enhanced guaiacol oxidation in Klebsiella sp. LEA1 and Pseudomonas sp. LEA2. Lignin-related monomers and intermediates such as 2,6-dimethoxyphenol, 4-vinyl guaiacol, 4-hydroxybenzoic acid, benzoic acid, catechol, and succinic acid were detected mostly during the late stage of incubation of Klebsiella sp. LEA1 and Pseudomonas sp. LEA2 in lignin minimal salt media via GC-MS analysis. The intermediates identified from Klebsiella sp. LEA1 degradation suggested that conversion and utilization occurred through the β-ketoadipate (ortho-cleavage) pathway under limited oxygen conditions. The ability of these bacteria to thrive on alkaline lignin and produce various lignin-related intermediates under limited oxygen conditions suggests their potential utility in oxygen-limited processes and the production of renewable chemicals from plant biomass.

Production of a novel laccase from Ceratorhiza hydrophila and assessing its potential in natural dye fixation and cytotoxicity against tumor cells

BACKGROUND

Flavonoid natural dyes have gained attention because they are nontoxic and eco-friendly. However, they do not work effectively with artificial fibers and require the use of mordants, which are considered as hazardous chemicals. Laccase enzyme catalyzes the oxidation of phenols, forming phenoxyl radicals that undergo a further polymerization process. So, laccase can oxidize flavonoid dyes, and it can be used instead of harmful mordants in flavonoid dye fixation on cotton fabrics. Laccases also are involved in a variety of metabolic processes, and they have anti-proliferative effects toward HepG2 and MCF-7 tumor cells.

RESULTS

Among fifteen fungal isolates, the fungus Ceratorhiza hydrophila isolated from the submerged plant Myriophyllum spicatum was selected as the most potent laccase producer. Optimization of the production medium resulted in a 9.9-fold increase in laccase productivity. The partially purified Ceratorhiza hydrophila laccase could successfully improve the affinity of cotton fabrics toward quercetin (flavonoid) dye with excellent color fastness properties. The partially purified laccase also showed anti-proliferative activity against HepG2 and MCF-7 tumor cells. However, high laccase concentration is required to estimate IC50.

CONCLUSIONS

Ceratorhiza hydrophila MK387081 is an excellent laccase producer. The partially purified laccase from Ceratorhiza hydrophila can be used in textile dyeing and printing processes as a safer alternative to the conventional hazardous mordants. Also, it can be used in preparation of cancer treatment drugs. However, further studies are needed to investigate IC50 for both cell types at higher laccase concentrations.

Optimization, purification and characterization of laccase from Ganoderma leucocontextum along with its phylogenetic relationship

The aim of this work to study an efficient laccase producing fungus Ganoderma leucocontextum, which was identified by ITS regions of DNA and phylogenetic tree was constructed. This study showed the laccase first-time from G. leucocontextum by using medium containing guaiacol. The growth cultural (pH, temperature, incubation days, rpm) and nutritional (carbon and nitrogen sources) conditions were optimized, which enhanced the enzyme production up to 4.5-folds. Laccase production increased 855 U/L at 40 °C. The pH 5.0 was suitable for laccase secretion (2517 U/L) on the 7th day of incubation at 100 rpm (698.3 U/L). Glucose and sucrose were good carbon source to enhance the laccase synthesis. The 10 g/L beef (4671 U/L) and yeast extract (5776 U/L) were the best nitrogen source for laccase secretion from G. leucocontextum. The laccase was purified from the 80% ammonium sulphate precipitations of protein identified by nucleotides sequence. The molecular weight (65.0 kDa) of purified laccase was identified through SDS and native PAGE entitled as Glacc110. The Glacc110 was characterized under different parameters. It retained > 90% of its activity for 16 min incubation at 60 °C in acidic medium (pH 4.0). This enzyme exerted its optimal activity at pH 3.0 and temperature 70 °C with guaiacol substrate. The catalytic parameters K_m and V_max was 1.658 (mM) and 2.452 (mM/min), respectively. The thermo stability of the laccase produced by submerged fermentation of G. leucocontextum has potential for industrial and biotechnology applications. The results remarked the G. leucocontextum is a good source for laccase production.

Impact of pH regulation on multicopper oxidase production and swarming motility in the bacterium Proteus hauseri ZMd44

Proteus hauseri ZMd44, a biodecolorizing bacterium, has been known to produce electricity and multicopper oxidase (Mco-laccase) under copper induction. However, optimization and regulation of production have not been explored. This study is the first attempt to evaluate several parameters on biomass and Mco-laccase production of P. hauseri ZMd44. Through orthogonal experiments with Taguchi's L9, it was found that P. hauseri ZMd44 was sensitive to pH value. The cells grew relatively quickly at pH 7, thus the biomass and Mco-laccase production reached 1.66 g/L and 1043.6 U/L, respectively. Higher pH values also influenced the swarming motility, which is an important characteristic of P. hauseri ZMd44 that affects urinary tract infection. The swarming circle and the diameter of the swarm, represented by the motility velocity, were found to be more controlled after 24 h of growth at pH 6. The swarming ability of P. hauseri was completely inhibited by the addition of 3 mM copper or zinc ions. Therefore, the Mco-laccase and swarming motility could be controlled by regulating pH and ion content.

Eichhornia crassipes: Agro-waster for a novel thermostable laccase production by Pycnoporus sanguineus SYBC-L1

The aim of this study was to explore the utilization of an intractable waster of Eichhornia crassipes in laccase production by Pycnoporus sanguineus SYBC-L1. E. crassipes as the sole carbon and nitrogen source was confirmed to produce laccase (7.26 U/g dry substrate). The fermentation medium for the maximum enzyme production was optimized and the laccase was then purified and characterized. The optimized culture medium was 25.1% E. crassipes, 13.9% sawdust, 1.5 mM CuSO₄, 40 μM gallic acid, 65% moisture content and initial pH 6.0. A maximum laccase activity of 32.02 U/g dry substrate was detected at 9th day, which was 4.5-fold compared to the initial medium. The molecular mass of the purified Lac-S was 58.4 kDa. The optimum activity of Lac-S for DMP was at pH 3.0 and 70°C. Lac-S showed not only high catalytic activities at low temperature, but also good stabilities toward pH and temperature. The residual catalytic activities of Lac-S were 30%, 40% and 50% at 0°C, 10°C and 20°C, and the half-lives at 50°C, 60°C and 70°C were 21.7, 9.7 and 1.5 h, respectively. The results provide a significant basis for E. crassipes further utilization and Lac-S specific application in harsh industry.

Significance and Roles of Proteus spp. Bacteria in Natural Environments

Proteus spp. bacteria were first described in 1885 by Gustav Hauser, who had revealed their feature of intensive swarming growth. Currently, the genus is divided into Proteus mirabilis, Proteus vulgaris, Proteus penneri, Proteus hauseri, and three unnamed genomospecies 4, 5, and 6 and consists of 80 O-antigenic serogroups. The bacteria are known to be human opportunistic pathogens, isolated from urine, wounds, and other clinical sources. It is postulated that intestines are a reservoir of these proteolytic organisms. Many wild and domestic animals may be hosts of Proteus spp. bacteria, which are commonly known to play a role of parasites or commensals. However, interesting examples of their symbiotic relationships with higher organisms have also been described. Proteus spp. bacteria present in soil or water habitats are often regarded as indicators of fecal pollution, posing a threat of poisoning when the contaminated water or seafood is consumed. The health risk may also be connected with drug-resistant strains sourcing from intestines. Positive aspects of the bacteria presence in water and soil are connected with exceptional features displayed by autochthonic Proteus spp. strains detected in these environments. These rods acquire various metabolic abilities allowing their adaptation to different environmental conditions, such as high concentrations of heavy metals or toxic substances, which may be exploited as sources of energy and nutrition by the bacteria. The Proteus spp. abilities to tolerate or utilize polluting compounds as well as promote plant growth provide a possibility of employing these microorganisms in bioremediation and environmental protection.

Oxidation of polycyclic aromatic hydrocarbons using Bacillus subtilis CotA with high laccase activity and copper independence

Bacterial laccase CueO from Escherichia coli can oxidize polycyclic aromatic hydrocarbons (PAHs); however, its application in the remediation of PAH-contaminated soil mainly suffers from a low oxidation rate and copper dependence. It was reported that a laccase with a higher redox potential tended to have a higher oxidation rate; thus, the present study investigated the oxidation of PAHs using another bacterial laccase CotA from Bacillus subtilis with a higher redox potential (525 mV) than CueO (440 mV). Recombinant CotA was overexpressed in E. coli and partially purified, exhibiting a higher laccase-specific activity than CueO over a broad pH and temperature range. CotA exhibited moderate thermostability at high temperatures. CotA oxidized PAHs in the absence of exogenous copper. Thereby, secondary heavy metal pollution can be avoided, another advantage of CotA over CueO. Moreover, this study also evaluated some unexplained phenomena in our previous study. It was observed that the oxidation of PAHs with bacterial laccases can be promoted by copper. The partially purified bacterial laccase oxidized only two of the 15 tested PAHs, i.e., anthracene and benzo[a]pyrene, indicating the presence of natural redox mediators in crude cell extracts. Overall, the recombinant CotA oxidizes PAHs with high laccase activity and copper independence, indicating that CotA is a better candidate for the remediation of PAHs than CueO. Besides, the findings here provide a better understanding of the oxidation of PAHs using bacterial laccases.

Insights into copper effect on Proteus hauseri through proteomic and metabolic analyses

This is the first-attempt to use liquid chromatography coupled with tandem mass (LC-MS-MS) in deciphering the effects of copper ion on Proteus hauseri. Total 941 proteins in copper-addition (+Cu) group and 898 proteins in non-copper-addition (-Cu) group were found, which containing 221 and 178 differential proteins in +Cu and -Cu group, respectively. Differential proteins in both groups were defined into 14 groups by their functional classification which transport/membrane function proteins were the major different part between the two groups, which took 19.5% and 7.7%, respectively. The result of BioCyc and KEGG analyses on metabolic pathway indicated that copper could interrupted the pathway of chemotaxis CheY and inhibited the swarming of P. hauseri, which provided a potential in controlling the pathogenicity of this strain.

Expanding the laccase-toolbox: a laccase from Corynebacterium glutamicum with phenol coupling and cuprous oxidase activity

Laccases are oxidases with potential for application in biotechnology. Up to now only fungal laccases have been applied in technical processes, although bacterial laccases are generally easier to handle and more stable at alkaline pH values and elevated temperatures. To increase the toolbox of bacterial laccases and to broaden our knowledge about them, new enzymes have to be characterized. Within this study, we describe the new bacterial laccase CgL1 from Corynebacterium glutamicum. CgL1 was found to oxidize typical laccase substrates like 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), syringaldazine and 2,6-dimethoxyphenol. The enzyme also demonstrates cuprous oxidase activity. Furthermore, CgL1 is active for several hours at temperatures up to 60°C and at alkaline pH, as well as stable in different organic solvents. This makes CgL1 a potential candidate for technical applications. In addition, CgL1 was found to catalyze the CC/CO coupling of several phenolic compounds which can serve as precursors for the synthesis of natural products like antibiotics and phytohormones. This activity and product distribution were influenced by pH value and mediators used.

Copper response of Proteus hauseri based on proteomic and genetic expression and cell morphology analyses

The copper response of Proteus hauseri ZMd44 was determined using one-dimensional (1D) gel electrophoresis coupled with MALDI-TOF-TOF mass spectrometry for a similarity analysis of proteins isolated from P. hauseri ZMd44 cultured in CuSO4-bearing LB medium. Candidate proteins identified as a copper-transporting P-type ATPase (CTPP), phosphoenolpyruvate carboxykinase (PEPCK), flagellin (Fla), and outer membrane proteins (Omps) were the major copper-associated proteins in P. hauseri. In a comparative analysis of subcellular (i.e., periplasmic, intracellular, and inner membranes) and cellular debris, proteomics analysis revealed a distinct differential expression of proteins in P. hauseri with and without copper ion exposure. These findings were consistent with the transcription level dynamics determined using quantitative real-time PCR. Based on a genetic cluster analysis of copper-associated proteins from P. hauseri, Fla and one of the Omps showed greater diversity in their protein sequences compared to those of other Proteus species. Transmission electron microscopy (TEM) and the observed growth on LB agar plates showed that the swarming motility of cells was significantly suppressed and inhibited upon Cu(II) exposure. Thus, copper stress could have important therapeutic significance due to the loss of swarming motility capacity in P. hauseri, which causes urinary tract infections.

Draft Genome Sequence of the Bioelectricity-Generating and Dye-Decolorizing Bacterium Proteus hauseri Strain ZMd44

Proteus hauseri ZMd44 (CGMCC 6746), as a crucial biodecolorizing, bioelectricity-generating, and copper-resistant bacterium, is distinguished from the urinary pathogens Proteus penneri and Proteus mirabilis. To further investigate the genetic functions of this strain, the genome sequence and annotation of its open reading frames, which consist of 3,875,927 bp (G+C content, 38.12%), are presented here.

Molecular cloning and heterologous expression of laccase from Aeromonas hydrophila NIU01 in Escherichia coli with parameters optimization in production

Prior studies disclosed that Aeromonas hydrophila NIU01 was a biodecolorization and bioelectricity bacterium which was isolated from a cross-strait of Taiwan. However, enzymatic function, laccase, involved in this strain had never been reported. This first attempt is to explore its laccase activity, the molecular cloning and heterologous recombinant expression in Escherichia coli. A full-length novel gene of 1,647 bp, LacA, encoding of 549 amino acids was successfully cloned by polymerase chain reaction. The recombinant pET-15b(+)-NIU-LacA expression was compared in different E. coli strains. By applying Taguchi's L9 in culture optimization, the soluble laccase increased to 22.7 %, in which the conditions were obtained at 22 °C with initial shaking speed at 200 rpm, addition of lactose of 0.2 mM and CuSO4 of 0.5 mM to the medium, and shaking off while cell mass reached to OD(600nm) of 1.5. NIU-LacA was strongly inhibited by chloride ion. The optimal temperature was 60 °C and the optimum pH for ABTS (2,2'-azino-bis (3-ethylbenzthiazolinesulfonic acid) and 2,6-DMP (2,6-dimethoxyphenol) were pH 2.1 and pH 7.5 which enzymatic activity was 274.6 and 44.8 U/L, respectively. Further study in structural modeling of NIU-LacA showed the C terminal domain was the major variance in the three most closely A. hydrophila strains.