Biotechnological potential of fungi from a mangrove ecosystem: Enzymes, salt tolerance and decolorization of a real textile effluent

Exploration of Mangrove Endophytes as Novel Sources of Tannase Producing Fungi

Tannase, a highly adaptive biocatalyst, plays a pivotal role in diverse bioconversion reactions in nature. This enzyme exhibits numerous applications across various industrial sectors, including food, pharmaceuticals, chemicals, and beverages. This study aimed to screen and characterize fungal endophytes isolated from mangrove plants for their enzyme tannase-producing ability. Eighty-five filamentous endophytic fungi were isolated from different mangrove samples and subsequently identified. These fungal strains were initially screened using the tannic acid agar plate method. Out of the screened strains, 13 fungal isolates demonstrated tannase production ability. The quantitative estimation of extracellular tannase was performed using the submerged fermentation technique. Among the studied endophytes, eight isolates, namely LV_084 (21.21 IU/mL), LV_074 (15.41 IU/mL), LV_078 (6.98 IU/mL), LV_038 (6.97 IU/mL), LV_077 (6.32 IU/mL), LV_016 and LV_066 (6.37 IU/mL), and LV_060 (6.18 IU/mL) exhibited excellent tannase activity. Among these isolates, LV_084 Phyllosticta capitalensis and LV_074 Aspergillus chevalieri showed the highest enzyme-producing ability. These isolates were authenticated using ITS rDNA sequencing, followed by BLAST search and phylogenetic analysis. Furthermore, the physical and chemical conditions for the maximum enzyme production were optimized. This is the first report of enzyme tannase production by Phyllosticta capitalensis and Aspergillus chevalieri.

Isolation and Characterization of a Promising Lignocellulolytic Enzyme Producer Pseudolagarobasidium acaciicola SL3-03 from Mangrove Soil in Thailand

Lignocellulolytic enzymes isolation from mangrove-derived organisms has many industrial advantages due to their efficiency in dealing with extreme and challenging conditions, such as high temperatures and salt concentrations. This study aimed to isolate fungal enzyme producers from mangrove soil in Thailand to produce lignocellulolytic enzymes (carboxymethyl cellulase: CMCase, xylanase, and laccase) and to characterize these enzymes to support industrial applications. Forty-eight fungi were isolated from the mangrove samples, and their enzyme-producing capabilities were assessed using primary and secondary screening methods. The findings revealed that Pseudolagarobasidium acaciicola SL3-03 emerged as a promising producer of lignocellulolytic enzymes. It exhibited the ability to produce 1.345 U/mL of CMCase, 1.293 U/mL of xylanase, and 43.126 U/mL of laccase. Furthermore, the enzymatic characteristics of P. acaciicola SL3-03 were analyzed. The CMCase exhibited optimal activity at 50 °C and pH 5.5, the xylanase at 50 °C and pH 4.8, and the laccase at 55 °C and pH 5. Besides, the CMCase and xylanase from P. acaciicola SL3-03 expressed high halotolerance abilities that could maintain activity and stability under high salt concentrations (149% activity at 5 M NaCl). Future studies may focus on structural analysis of the enzymes to further characterize and identify their specific types. The results suggest that mangrove soil harbors significant potential for discovering proficient lignocellulolytic enzyme producers with desirable characteristics, which can be advantageous for industrial applications.

Halophilic Pectinase-Producing Bacteria from Arthrocnemum macrostachyum Rhizosphere: Potential for Fruit-Vegetable Juice Processing

This study aimed to isolate salt-tolerant pectinolytic bacteria from the rhizosphere of a salt marsh plant and utilize their pectinases for the clarification of detox juice preparation. Sixteen halophilic bacterial strains were isolated from the rhizospheric soil of Arthrocnemum macrostachyum. The isolates were screened for pectinase activity, and two strains, ASA21 and ASA29, exhibited the highest pectinase production in the presence of 2.5% NaCl, reaching 13.3 and 14.1 IU mL-1, respectively. The strains were identified as Bacillus paralicheniformis and Paenibacillus sp. by 16S rDNA sequencing and phylogenetic analysis. Growth kinetics and pectinase production studies revealed that both strains produced pectinase during the log phase, with ASA29 demonstrating higher growth and pectinase titers. The pectinase from ASA29 exhibited enhanced activity in the presence of 3% NaCl. The pectinases from both strains were applied for the clarification of detox juice prepared from beetroot, carrots, and apples. The use of 20 IU mL-1 pectinase from ASA29 for 2-3 h yielded > 96% juice with high total phenolic content and antioxidant activities. This study highlights the potential of salt-tolerant pectinolytic bacteria from the rhizosphere for biotechnological applications, particularly in the clarification of juices with high salt content.

Blue and Yellow Laccases from Alternaria sp. Strain HU: Characterization and Immobilization on Magnetic Nanoparticles

Laccases are important and valuable enzymes with a great potential for biotechnological applications. In this study, two novel laccases, LacHU1 and LacHU2, from Alternaria sp. HU have been purified and characterized. The molecular mass of each isoenzyme was ~66 kDa. LacHU1 laccases was yellow and had no typical blue oxidase spectra and LacHU2 had a blue color and characteristic absorption spectra. The catalytic efficiency of LacHU1 for most substrates was higher than that of LacHU2 laccase. Both isoenzymes effectively oxidize flavonoids. Alternaria sp. laccases were successfully immobilized on magnetic nanoparticles. The thermostability of immobilized laccases increased and optimal pH shifted to more alkaline compared to the free laccases. Potential applications of laccases from Alternaria sp. HU are in the oxidation of flavonoids in cotton or in water treatment processes.

Exploring fungal-mediated solutions and its molecular mechanistic insights for textile dye decolorization

Decolorization of textile dyes and study of their intermediate compounds is necessary to comprehend the mechanism of dye degradation. In the present study, different fungal mediated solutions were explored to provide an alternative to treat the reactive dyes. Growing biomass of Pleurotus sajor caju showed 83% decolorization (249.99 mg L-1 removal) of Reactive Blue 13 (RB 13) and 63% decolorization (188.83 mg L-1) of Reactive Black 5 (RB 5) at 300 mg L-1 initial concentration on 8 d. Higher laccase activity was positively correlated with increase in decolorization. However, increasing dye concentration has inhibitory effect on fungal biomass due to increase in toxicity. In laccase mediated decolorization, laccase produced from P. sajor caju using carbon rich waste material as substrate showed 89% decolorization (276.36 mg L-1 removal) of RB 13 and 33% decolorization (105.37 mg L-1 removal) of RB 5 at 300 mg L-1 initial dye concentration in 100 min at 30 °C and pH 3.0'. Comparing the two methods, laccase-mediated decolorization shows better decolorization in less time and does not produce sludge. Further, the present work also attempted to study the dye degradation pathway for Reactive blue 13 via laccase mediated process. Fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) were utilized to identify the degraded products. The GC-MS analysis showed the formation of naphthalene, naphthalene 2-ol, benzene,1-2, dicarboxylic acid, 4, amino, 6,chloro, 1-3-5, triazin-2-ol as the final degraded products after enzymatic degradation of RB 13. These findings provide in-depth study of laccase-mediated textile dye degradation mechanism.

Metagenomic-based discovery and comparison of the lignin degrading potential of microbiomes in aquatic and terrestrial ecosystems via the LCdb database

Lignin, as an abundant organic carbon, plays a vital role in the global carbon cycle. However, our understanding of the global lignin-degrading microbiome remains elusive. The greatest barrier has been absence of a comprehensive and accurate functional gene database. Here, we first developed a curated functional gene database (LCdb) for metagenomic profiling of lignin degrading microbial consortia. Via the LCdb, we draw a clear picture describing the global biogeography of communities with lignin-degrading potential. They exhibit clear niche differentiation at the levels of taxonomy and functional traits. The terrestrial microbiomes showed the highest diversity, yet the lowest correlations. In particular, there were few correlations between genes involved in aerobic and anaerobic degradation pathways, showing a clear functional redundancy property. In contrast, enhanced correlations, especially closer inter-connections between anaerobic and aerobic groups, were observed in aquatic consortia in response to the lower diversity. Specifically, dypB and dypA, are widespread on Earth, indicating their essential roles in lignin depolymerization. Estuarine and marine consortia featured the laccase and mnsod genes, respectively. Notably, the roles of archaea in lignin degradation were revealed in marine ecosystems. Environmental factors strongly influenced functional traits, but weakly shaped taxonomic groups. Null mode analysis further verified that composition of functional traits was deterministic, while taxonomic composition was highly stochastic, demonstrating that the environment selects functional genes rather than taxonomic groups. Our study not only develops a useful tool to study lignin degrading microbial communities via metagenome sequencing but also advances our understanding of ecological traits of these global microbiomes.

Tannery effluent treatments with mangrove fungi, grass root biomass, and biochar

Tannery effluents contain high amounts of polluting chemicals, such as salts and heavy metals released often to surface waters. New economic and eco-friendly purification methods are needed. Two adsorbing materials and five salt-tolerant fungal isolates from mangrove habitat were studied. Purification experiments were carried out using the pollutant adsorbents biochar and the biomass of vetiver grass (Chrysopogon zizanioides) roots and the fungi Cladosporium cladosporioides, Phomopsis glabrae, Aspergillus niger, Emericellopsis sp., and Scopulariopsis sp., which were isolated from mangrove sediment. They efficacy to reduce pollutants was studied in different combinations. Salinity, turbidity, total dissolved solids, total suspended solids, phenols, nitrogen, ammonia. Biological and chemical oxygen demand (BOD, COD) and several heavy metals were measured. The adsorbents were efficient reducing the pollutants to 15-50% of the original. The efficiency of the combination of biochar and roots was generally at the same level as the adsorbents alone. Some pollutants such as turbidity, COD and ammonium were reduced slightly more by the combination than the adsorbents alone. From all 14 treatments, Emericellopsis sp. with biochar and roots appeared to be the most efficient reducing pollutants to < 10-30%. BOD and COD were reduced to ca 5% of the original. The treatment was efficient in reducing also heavy metals (As, Cd, Cr, Mn Pb, Zn). The fungal species originating from the environment instead of the strains present in the tannery effluent reduced pollutants remarkably and the adsorbents improved the reduction efficiency. However, the method needs development for effluents with high pollutant concentrations to fulfil the environmental regulations.

Halophilic filamentous fungi and their enzymes: Potential biotechnological applications

Recently, interest in the study of microorganisms growing under extreme conditions, particularly halophiles, has increased due to their potential use in industrial processes. Halophiles are the class of microorganisms that grow optimally at high NaCl concentrations and are capable of producing halophilic enzymes capable of catalyzing reactions under harsh conditions. So far, fungi are the least studied halophilic microorganisms, even though they have been shown to counteract these extreme conditions by producing secondary metabolites with very interesting properties. This review highlights mechanisms that allow halophilic fungi to adapt high salinity and the specificity of their enzymes to a spectrum of action in industrial and environmental applications. The peculiarities of these enzymes justify the urgent need to apply green alternative compounds in industries.

Hyper-Production of Pullulan by a Novel Fungus of Aureobasidium melanogenum ZH27 through Batch Fermentation

Pullulan, which is a microbial exopolysaccharide, has found widespread applications in foods, biomedicines, and cosmetics. Despite its versatility, most wild-type strains tend to yield low levels of pullulan production, and their mutants present genetic instability, achieving a limited increase in pullulan production. Therefore, mining new wild strains with robust pullulan-producing abilities remains an urgent concern. In this study, we found a novel strain, namely, Aureobasidium melanogenum ZH27, that had a remarkable pullulan-producing capacity and optimized its cultivation conditions using the one-factor-at-a-time method. To elucidate the reasons that drove the hyper-production of pullulan, we scrutinized changes in cell morphology and gene expressions. The results reveal that strain ZH27 achieved 115.4 ± 1.82 g/L pullulan with a productivity of 0.87 g/L/h during batch fermentation within 132 h under the optimized condition (OC). This pullulan titer increased by 105% compared with the initial condition (IC). Intriguingly, under the OC, swollen cells featuring 1-2 large vacuoles predominated during a rapid pullulan accumulation, while these swollen cells with one large vacuole and several smaller ones were prevalent under the IC. Moreover, the expressions of genes associated with pullulan accumulation and by-product synthesis were almost all upregulated. These findings suggest that swollen cells and large vacuoles may play pivotal roles in the high level of pullulan production, and the accumulation of by-products also potentially contributes to pullulan synthesis. This study provides a novel and promising candidate for industrial pullulan production.

Characterization of a Novel One-Domain Halotolerant Laccase from Parageobacillus thermoglucosidasius and Its Application in Dye Decolorization

Laccases are widespread multi-copper oxidases and generally classified into three-domain laccases and two-domain laccases. In this study, a novel laccase PthLac from Parageobacillus thermoglucosidasius harbored only one domain of Cu-oxidase_4 and showed no sequence relatedness or structure similarity to three-domain and two-domain laccases. PthLac was heterologously expressed in Escherichia coli, purified, and characterized. The optimum temperature and pH of PthLac on guaiacol were at 60 ℃ and pH 6, respectively. The effects of various metal ions on PthLac were analyzed. All the tested metal ions did not suppress the activity of PthLac, except for 10 mM Cu2+, which increased the activity of PthLac to 316%, indicating that PthLac was activated by Cu2+. Meanwhile, PthLac kept 121% and 69% activity when incubated at concentrations of 2.5 and 3 M NaCl for 9 h, suggesting the long-term halotolerancy of this enzyme. In addition, PthLac showed resistance to the organic solvents and surfactants, and displayed dye decolorization capacity. This study enriched our knowledge about one-domain laccase and its potential industrial applications.

Improving algal growth in an anaerobic digestion piggery effluent by fungal pretreatment: Process optimization, the underlying mechanism of fungal decolorization, and nitrogen removal

Anaerobic digestion piggery effluent (ADPE) shows high chromaticity and ammonium levels, severely inhibiting algal growth. Fungal pretreatment has great potential for decolorization and nutrient removal from wastewater, which coupled with microalgal cultivation may be a reliable strategy for sustainable ADPE resource utilization. In this study, we selected and identified two locally isolated eco-friendly fungal strains for ADPE pretreatment, and fungal culture conditions were optimized for decolorization and ammonium nitrogen (NH4+-N) removal. Subsequently, the underlying mechanisms of fungal decolorization and nitrogen removal were investigated, and the feasibility of using pretreated ADPE for algal cultivation was explored. The results showed that two fungal strains were identified as Trichoderma harzianum and Trichoderma afroharzianum, respectively, presenting good growth and decolorization performance for ADPE pretreatment. The optimized culture conditions were as follows: 20% ADPE, 8 g L-1 glucose, initial pH 6, 160 rpm, 25-30 °C, and 0.15 g L-1 initial dry-weight. ADPE decolorization was mainly caused by fungal biodegradation of color-related humic substances through manganese peroxidase secretion. The removed nitrogen was completely converted into fungal biomass as nitrogen assimilated, ca. 90% of which was attributed to NH4+-N removal. The pretreated ADPE significantly improved algal growth and nutrient removal, demonstrating the feasibility of developing an eco-friendly fungi-based pretreatment technology.

Tramates trogii biomass in carboxymethylcellulose-lignin composite beads for adsorption and biodegradation of bisphenol A

Tramates trogii biomass was immobilized in carboxymethyl cellulose-lignin composite beads via cross-linking with Fe(III) ions (i.e., Fe(III)-CMC@Lig(1-4)@FB). The composite beads formulations were used for the adsorption and degradation of bisphenol A (BPA) using the free fungal biomass as a control system. The maximum adsorption capacity of the free fungal biomass and Fe(III)-CMC@Lig-3@FB for BPA was found to be 57.8 and 95.6, mg/g, respectively. The degradation rates of BPA were found to be 87.8 and 89.6% for the free fungal biomass and Fe(III)CMC@Lig-3@FB for 72 h in a batch reactor, respectively. Adsorption of BPA on the free fungal biomass and Fe(III)CMC@Lig-3@FB fungal preparations described by the Langmuir and Temkin isotherm models, and the pseudo-second-order kinetic model. The values of Gibbs free energy of adsorption (ΔG°) were - 20.7 and - 25.8 kJ/mol at 298 K for BPA on the free fungal biomass and Fe(III)-CMC@Lig-3@FB beads, respectively. Moreover, the toxicities of the BPA and degradation products were evaluated with three different test organisms: (i) a freshwater micro-crustacean (Daphnia magna), (ii) a freshwater algae (Chlamydomonas reinhardti), and (iii) a Turkish winter wheat seed (Triticum aestivum L.). After treatment with the Fe(III)CMC@Lig-3@FB formulation, the degradation products had not any significant toxic effect compared to pure BPA. This work shows that the prepared composite bioactive system had a high potential for degradation of BPA from an aqueous medium without producing toxic end-products. Thus, it could be a good candidate for environmentally safe biological methods.

Potential of Fungal Endophytes Isolated from Pasture Species in Spanish Dehesas to Produce Enzymes under Salt Conditions

Endophytic fungi have been found to produce a wide range of extracellular enzymes, which are increasingly in demand for their industrial applications. Different by-products from the agrifood industry could be used as fungal growth substrates for the massive production of these enzymes, specifically as a way to revalorize them. However, such by-products often present unfavorable conditions for the microorganism’s growth, such as high salt concentrations. Therefore, the objective of the present study was to evaluate the potential of eleven endophytic fungi—which were isolated from plants growing in a harsh environment, specifically, from the Spanish dehesas—for the purposes of the in vitro production of six enzymes (i.e., amylase, lipase, protease, cellulase, pectinase and laccase) under both standard and salt-amended conditions. Under standard conditions, the studied endophytes produced between two and four of the six enzymes evaluated. In most of the producer fungal species, this enzymatic activity was relatively maintained when NaCl was added to the medium. Among the isolates evaluated, Sarocladium terricola (E025), Acremonium implicatum (E178), Microdiplodia hawaiiensis (E198), and an unidentified species (E586) were the most suitable candidates for the massive production of enzymes by using growth substrates with saline properties (such as those found in the many by-products from the agrifood industry). This study should be considered an initial approach by which to further study the identification of these compounds as well as to develop the optimization of their production by directly using those residues.

Diversity and Potential Function of Prokaryotic and Eukaryotic Communities from Different Mangrove Sediments

Mangrove trees generally play important roles in protecting intertidal ecosystems. The mangrove root-associated sediments provide a repertoire of microbial communities that contribute to pivotal ecological functions in the system. In the present study, we used the high-throughput sequencing and PICRUSt-predicted functional information (based on 16S/18S rDNA profiles) to investigate the bacterial, archaeal, and fungal communities in two mangrove systems, located in the estuary of the Jiulong River (China), with different contaminated conditions and frequencies of human activity. Diverse distribution patterns for microbial communities were observed in six sediment samples collected from the two survey areas, which were found to be related mainly to the substrates in mangrove sediments. The sediments were predominated by relatively higher ratios of heterotrophic bacteria that participated in the degradation of organic matters, including phylum of Chloroflexi, Acidobacteriota, Desulfobacterota, and Proteobacteria. In addition, Crenarchaeota and Ascomycota presented the highest abundances of archaea and fungi, respectively. The relatively high concentrations of calcium, nitrogen, magnesium, and phosphorus in mangrove sediments correlated significantly with the microbial communities. In addition, although the potential functions were similar in the two sites based on COG and KEGG pathways, the abundances of enzymes involved in the degradation processes of cellulose and hemicellulose and the metabolism of nitrogen and sulfur presented distinctions. These results provide insights into the environmental conditions shaping microbial assemblies of the mangrove sediments under the impacts of human activities; for instance, a more abundant amount of calcium was found in urban areas in this study.

Endophytic fungi from Dongxiang wild rice (Oryza rufipogon Griff.) show diverse catalytic potential for converting glycyrrhizin

Endophytic fungi inhabiting niche environments are novel biocatalyst resources that need to be exploited urgently. In this study, 63 endophytic fungi isolated from Dongxiang wild rice (Oryza rufipogon Griff.) were tested to assess their potentials to transform glycyrrhizin (GL) into glycyrrhetinic acid monoglucuronide (GAMG) or glycyrrhetinic acid (GA), of which 12 strains were shown to have β-d-glucuronidase activity. Based on morphological characteristics and rDNA ITS sequence analysis, the strains S59, L138, L55 and R57 with high GL molar conversion rates (55%, 45%, 65% and 89%) were further identified as Microsphaeropsis arundinis S59, Penicillium rubens L138, Aspergillus flavus L55 and Eupenicillium javanicum R57, respectively. These four strains with four different types of GL conversion processes were identified, i.e., (1) GL → GAMG in M. arundinis S59, (2) GL → GAMG and GA in A. flavus L55, (3) GL → GA in P. rubens L138, and (4) GL → GAMG → GA in E. javanicum R57, in which the bioconversion type (4) is reported for the first time. The study not only provided abundant and diverse β-d-glucuronidase resources that can be used for GL bioconversion, especially for GAMG biosynthesis from endophytic fungi, but also expanded our knowledge of potential roles of endophytes as new biocatalysts in biotransformation.