Reactive oxygen species and development in microbial eukaryotes

Enhancement of protein production in Aspergillus niger by engineering the antioxidant defense metabolism

BACKGROUND

Research on protein production holds significant importance in the advancement of food technology, agriculture, pharmaceuticals, and bioenergy. Aspergillus niger stands out as an ideal microbial cell factory for the production of food-grade proteins, owing to its robust protein secretion capacity and excellent safety profile. However, the extensive oxidative folding of proteins within the endoplasmic reticulum (ER) triggers ER stress, consequently leading to protein misfolding reactions. This stressful phenomenon results in the accelerated generation of reactive oxygen species (ROS), thereby inducing oxidative stress. The accumulation of ROS can adversely affect intracellular DNA, proteins, and lipids.

RESULT

In this study, we enhanced the detoxification of ROS in A. niger (SH-1) by integrating multiple modules, including the NADPH regeneration engineering module, the glutaredoxin system, the GSH synthesis engineering module, and the transcription factor module. We assessed the intracellular ROS levels, growth under stress conditions, protein production levels, and intracellular GSH content. Our findings revealed that the overexpression of Glr1 in the glutaredoxin system exhibited significant efficacy across various parameters. Specifically, it reduced the intracellular ROS levels in A. niger by 50%, boosted glucoamylase enzyme activity by 243%, and increased total protein secretion by 88%.

CONCLUSION

The results indicate that moderate modulation of intracellular redox conditions can enhance overall protein output. In conclusion, we present a strategy for augmenting protein production in A. niger and propose a potential approach for optimizing microbial protein production system.

Contrasting effects of NADPH oxidases on the fungal hyphae growth and immune responses in Pleurotus ostreatus

Pleurotus ostreatus is one of the most consumed mushroom species, as it serves as a high-quality food, favors a rich secondary metabolism, and has remarkable adaptability to the environment and predators. In this study, we investigated the function of two key reactive oxygen species producing enzyme NADPH oxidase (PoNoxA and PoNoxB) in P. ostreatus hyphae growth, metabolite production, signaling pathway activation, and immune responses to different stresses. Characterization of the Nox mutants showed that PoNoxB played an important role in the hyphal formation of the multicellular structure, while PoNoxA regulated apical dominance. The ability of P. ostreatus to tolerate a series of abiotic stress conditions (e.g., osmotic, oxidative, membrane, and cell-wall stresses) and mechanical damage repair was enhanced with PoNoxA over-expression. PoNoxB had a greater responsibility in regulating the polysaccharide composition of the cell wall and methyl jasmonate and gibberellin GA1 biosynthesis, and improved mushroom resistance against Tyrophagus putrescentiae. Moreover, mutants were involved in the jasmonate and GA signaling pathway, and toxic protein defense metabolite production. Our findings shed light on how the oyster mushroom senses stress signals and responds to adverse environments by the complex regulators of Noxs.

A network of transcription factors in complex with a regulating cell cycle cyclin orchestrates fungal oxidative stress responses

BACKGROUND

Response to oxidative stress is universal in almost all organisms and the mitochondrial membrane protein, BbOhmm, negatively affects oxidative stress responses and virulence in the insect fungal pathogen, Beauveria bassiana. Nothing further, however, is known concerning how BbOhmm and this phenomenon is regulated.

RESULTS

Three oxidative stress response regulating Zn2Cys6 transcription factors (BbOsrR1, 2, and 3) were identified and verified via chromatin immunoprecipitation (ChIP)-qPCR analysis as binding to the BbOhmm promoter region, with BbOsrR2 showing the strongest binding. Targeted gene knockout of BbOsrR1 or BbOsrR3 led to decreased BbOhmm expression and consequently increased tolerances to free radical generating compounds (H2O2 and menadione), whereas the ΔBbOsrR2 strain showed increased BbOhmm expression with concomitant decreased tolerances to these compounds. RNA and ChIP sequencing analysis revealed that BbOsrR1 directly regulated a wide range of antioxidation and transcription-associated genes, negatively affecting the expression of the BbClp1 cyclin and BbOsrR2. BbClp1 was shown to localize to the cell nucleus and negatively mediate oxidative stress responses. BbOsrR2 and BbOsrR3 were shown to feed into the Fus3-MAPK pathway in addition to regulating antioxidation and detoxification genes. Binding motifs for the three transcription factors were found to partially overlap in the promoter region of BbOhmm and other target genes. Whereas BbOsrR1 appeared to function independently, co-immunoprecipitation revealed complex formation between BbClp1, BbOsrR2, and BbOsrR3, with BbClp1 partially regulating BbOsrR2 phosphorylation.

CONCLUSIONS

These findings reveal a regulatory network mediated by BbOsrR1 and the formation of a BbClp1-BbOsrR2-BbOsrR3 complex that orchestrates fungal oxidative stress responses.

Lipopeptide C17 Fengycin B Exhibits a Novel Antifungal Mechanism by Triggering Metacaspase-Dependent Apoptosis in Fusarium oxysporum

Fusarium wilt is a worldwide soil-borne fungal disease caused by Fusarium oxysporum that causes serious damage to agricultural products. Therefore, preventing and treating fusarium wilt is of great significance. In this study, we purified ten single lipopeptide fengycin components from Bacillus subtilis FAJT-4 and found that C17 fengycin B inhibited the growth of F. oxysporum FJAT-31362. We observed early apoptosis hallmarks, including reactive oxygen species accumulation, mitochondrial dysfunction, and phosphatidylserine externalization in C17 fengycin B-treated F. oxysporum cells. Further data showed that C17 fengycin B induces cell apoptosis in a metacaspase-dependent manner. Importantly, we found that the expression of autophagy-related genes in the TOR signaling pathway was significantly upregulated; simultaneously, the accumulation of acidic autophagy vacuoles in F. oxysporum cell indicated that the autophagy pathway was activated during apoptosis induced by C17 fengycin B. Therefore, this study provides new insights into the antifungal mechanism of fengycin.

Snowball: a novel gene family required for developmental patterning of fruiting bodies of mushroom-forming fungi (Agaricomycetes)

The morphogenesis of sexual fruiting bodies of fungi is a complex process determined by a genetically encoded program. Fruiting bodies reached the highest complexity levels in the Agaricomycetes; yet, the underlying genetics is currently poorly known. In this work, we functionally characterized a highly conserved gene termed snb1, whose expression level increases rapidly during fruiting body initiation. According to phylogenetic analyses, orthologs of snb1 are present in almost all agaricomycetes and may represent a novel conserved gene family that plays a substantial role in fruiting body development. We disrupted snb1 using CRISPR/Cas9 in the agaricomycete model organism Coprinopsis cinerea. snb1 deletion mutants formed unique, snowball-shaped, rudimentary fruiting bodies that could not differentiate caps, stipes, and lamellae. We took advantage of this phenotype to study fruiting body differentiation using RNA-Seq analyses. This revealed differentially regulated genes and gene families that, based on wild-type RNA-Seq data, were upregulated early during development and showed tissue-specific expression, suggesting a potential role in differentiation. Taken together, the novel gene family of snb1 and the differentially expressed genes in the snb1 mutants provide valuable insights into the complex mechanisms underlying developmental patterning in the Agaricomycetes.

IMPORTANCE

Fruiting bodies of mushroom-forming fungi (Agaricomycetes) are complex multicellular structures, with a spatially and temporally integrated developmental program that is, however, currently poorly known. In this study, we present a novel, conserved gene family, Snowball (snb), termed after the unique, differentiation-less fruiting body morphology of snb1 knockout strains in the model mushroom Coprinopsis cinerea. snb is a gene of unknown function that is highly conserved among agaricomycetes and encodes a protein of unknown function. A comparative transcriptomic analysis of the early developmental stages of differentiated wild-type and non-differentiated mutant fruiting bodies revealed conserved differentially expressed genes which may be related to tissue differentiation and developmental patterning fruiting body development.

Ferric reduction oxidase in Lilium pumilum affects plant saline-alkaline tolerance by regulating ROS homeostasis

Ferric reduction oxidase (FRO) plays important roles in biotic and abiotic stress. However, the function of ferric reduction oxidase from Lilium pumilum in response to NaHCO3 is unknown. Here we report the functional characterization of ferric reduction oxidase 7 in Lilium pumilum (LpFRO7) in stresses. Under NaHCO3 stress, the LpFRO7 overexpression lines exhibited lower accumulation of reactive oxygen species (ROS), higher activities in antioxidant enzyme (CAT, SOD and POD) and ferrite reductase, resulting in improved tolerance compared to the wild type (WT). In order to determine the functional network of LpFRO7, it was confirmed by EMSA assays, Yeast one-hybrid assays and Dual luciferase reporter assays that LpbHLH115 transcription factor can bind to the promoter of LpFRO7. Yeast two-hybrid assays, BiFC, and LCI assays were performed to prove that LpFRO7 can interact with LpTrx. Combining these findings, we concluded that LpFRO7 affects plant saline-alkaline tolerance by regulating ROS homeostasis.

Biocontrol potential of endophytic bacterium Bacillus altitudinis GS-16 against tea anthracnose caused by Colletotrichum gloeosporioides

Background

As one of the main pathogens causing tea anthracnose disease, Colletotrichum gloeosporioides has brought immeasurable impact on the sustainable development of agriculture. Given the adverse effects of chemical pesticides to the environment and human health, biological control has been a focus of the research on this pathogen. Bacillus altitudinis GS-16, which was isolated from healthy tea leaves, had exhibited strong antagonistic activity against tea anthracnose disease.

Methods

The antifungal mechanism of the endophytic bacterium GS-16 against C. gloeosporioides 1-F was determined by dual-culture assays, pot experiments, cell membrane permeability, cellular contents, cell metabolism, and the activities of the key defense enzymes.

Results

We investigated the possible mechanism of strain GS-16 inhibiting 1-F. In vitro, the dual-culture assays revealed that strain GS-16 had significant antagonistic activity (92.03%) against 1-F and broad-spectrum antifungal activity in all tested plant pathogens. In pot experiments, the disease index decreased to 6.12 after treatment with GS-16, indicating that strain GS-16 had a good biocontrol effect against tea anthracnose disease (89.06%). When the PE extract of GS-16 treated mycelial of 1-F, the mycelial appeared deformities, distortions, and swelling by SEM observations. Besides that, compared with the negative control, the contents of nucleic acids, protein, and total soluble sugar of GS-16 group were increased significantly, indicating that the PE extract of GS-16 could cause damage to integrity of 1-F. We also found that GS-16 obviously destroyed cellular metabolism and the normal synthesis of cellular contents. Additionally, treatment with GS-16 induced plant resistance by increasing the activities of the key defense enzymes PPO, SOD, CAT, PAL, and POD.

Conclusions

We concluded that GS-16 could damage cell permeability and integrity, destroy the normal synthesis of cellular contents, and induce plant resistance, which contributed to its antagonistic activity. These findings indicated that strain GS-16 could be used as an efficient microorganism for tea anthracnose disease caused by C. gloeosporioides.

Trichoderma virens Big Ras GTPase-1, a molecular switch for transforming a mutualistic fungus to plants in a deleterious microbe

Trichoderma spp. are ascomycete filamentous fungi widely distributed worldwide that establish mutualistic relationships with plants by antagonizing phytopathogens in the rhizosphere and colonizing the plant roots, hence, promoting plant growth and triggering the systemic resistance against phytopathogens. During the first stages of root colonization by Trichoderma, plants recognize the fungus as an invader by inducing the plant defense system, including the production of reactive oxygen species (ROS). Some members of the small Ras GTPases regulate NADPH oxidases and, therefore, ROS production. However, their role in mutualistic microorganisms that colonize plant roots is poorly understood. It has been demonstrated that Trichoderma virens strains lacking TBRG-1, a member of a new family of the Ras GTPases, impair their biocontrol capability and behave like a pathogen on tomato seeds and seedlings. Here, we found that TBRG-1 is essential in T. virens to maintain the mutualistic relationship with plants because a mutant-lacking tbrg-1 gen could not induce plant growth in Arabidopsis and tomatoes. Furthermore, treatment of Arabidopsis seedlings with Δtbrg-1 induced strongly PR-1a, the systemic acquired resistance (SAR) marker gene at early times of the interaction, which correlated with enhanced foliar damage by Botrytis cinerea, resembling the behavior of a biotrophic phytopathogen. Additionally, leaves of plants treated with either T. virens wild-type (wt) or Δtbrg-1 and challenged or not with Botrytis showed ROS production to a different extent, as well as differential expression of cell detoxification-related genes, CAT1, and APX1. Root colonization assays of sid-2 and jar1 mutant lines affected in SAR and induced systemic resistance (ISR) by Δtbrg-1 and the wt strain, suggest an important role of both pathways in the recognition of the fungus and that TBRG-1 plays a pivotal role in root colonization. Furthermore, we found that TBRG-1 is a negative regulator of NoxR expression, which may impact the mutualistic interaction.

A Putative NADPH Oxidase Gene in Unicellular Pathogenic Candida glabrata Is Required for Fungal ROS Production and Oxidative Stress Response

Most previous studies on fungal NADPH oxidases (Nox) focused on multicellular fungi and highlighted the important roles of Nox-derived reactive oxygen species (ROS) in cellular differentiation and signaling communication. However, there are few reports about Nox in unicellular fungi. A novel NOX ortholog, CAGL0K05863g (named CgNOX1), in Candida glabrata was investigated in this study. Deletion of CgNOX1 led to a decrease in both intracellular and extracellular ROS production. In addition, the Cgnox1∆ mutant exhibited hypersensitivity to hydrogen peroxide and menadione. Also, the wild-type strain showed higher levels of both CgNOX1 mRNA expression and ROS production under oxidative stress. Moreover, the absence of CgNOX1 resulted in impaired ferric reductase activity. Although there was no effect on in vitro biofilm formation, the CgNOX1 mutant did not produce hepatic apoptosis, which might be mediated by fungal Nox-derived ROS during co-incubation. Together, these results indicated that the novel NOX gene plays important roles in unicellular pathogenic C. glabrata and its interaction with host cells.

Multifunctional regulation of NADPH oxidase in growth, microsclerotia formation and virulence in Metarhizium rileyi

OBJECTIVES

Microsclerotia (MS), anti-stress structures produced by many filamentous fungi, have been proven to be a great substitute for conidia in the production of insecticides within entomogenous fungi. NADPH oxidase (Nox) is a highly conserved ROS-response protein family that is widespread in eukaryotes and plays distinct roles in environmental fitness among various filamentous fungi. However, it is not clear whether the formation of MS and pathogenicity in entomogenous fungi is regulated by the Nox inside. In this study, we reported the presence of NADPH oxidase homologs in a great potential biocontrol fungus, Metarhizium rileyi, and further showed multiple biological functions.

RESULTS

Three Nox homologous genes in M. rileyi showed high expression throughout the entire process of MS formation. Targeted deletion of MrNoxA, MrNoxB and MrNoxR all led to a decrease in MS yield and impaired morphology. Moreover, the anti-adversity assay showed that they are indispensable for growth, osmotic pressure and oxidative stress regulation in Metarhizium rileyi. Most importantly, △MrNoxR and △MrNoxA but not △MrNoxB showed a dramatic reduction in virulence via inoculation. The normality of appressoria might be unaffected in mutants since there are no striking differences in virulence compared with WT by topical injections.

CONCLUSION

Our results revealed that NADPH oxidase plays important roles in growth regulation, MS formation and pathogenicity in M. rileyi, perhaps in the ROS response and hyphal polarity.

Production of extracellular superoxide radical in microorganisms and its environmental implications: A review

Extracellular superoxide radical (O2•-) is ubiquitous in microbial environments and has significant implications for pollutant transformation. Microbial extracellular O2•- can be produced through multiple pathways, including electron leakage from the respiratory electron transport chain (ETC), NADPH oxidation by the transmembrane NADPH oxidase (NOX), and extracellular reactions. Extracellular O2•- significantly influences the geochemical processes of various substances, including toxic metals and refractory organic pollutants. On one hand, extracellular O2•- can react with variable-valence metals and detoxify certain highly toxic metals, such as As(III), Cr(VI), and Hg(II). On the other hand, extracellular O2•- can directly or indirectly (via Bio-Fenton) degrade many organic pollutants, including a variety of emerging contaminants. In this work, we summarize the production mechanisms of microbial extracellular O2•-, review its roles in the transformation of environmental pollutants, and discuss the potential applications, limiting factors, and future research directions in this field.

Filamentous actin destabilization by H2O2 favors DnmA aggregation, with crucial roles of cysteines 450 and 776 in mitochondrial and peroxisomal division in Aspergillus nidulans

IMPORTANCE

Mitochondria constitute major sources of H2O2 and other reactive oxygen species in eukaryotic cells. The division of these organelles is crucial for multiple processes in cell biology and relies on highly regulated mechano-GTPases that are oligomerization dependent and belong to the dynamin-related protein family, like A. nidulans DnmA. Our previous work demonstrated that H2O2 induces mitochondrial constriction, division, and remodeling of the outer membrane. Here, we show that H2O2 also induces a DnmA aggregation consistent with higher-order oligomerization and its recruitment to mitochondria. The study of this response uncovered that H2O2 induces the depolymerization and reorganization of actin as well as the critical role that cysteines 450 and 776 play in DnmA function. Our results provide new insights into the mechanisms of reactive oxygen species cell signaling and how they can regulate the dynamics of the actin cytoskeleton and the division of mitochondria and peroxisomes.

Microfluidic single-cell measurements of oxidative stress as a function of cell cycle position

Single-cell measurements routinely demonstrate high levels of variation between cells, but fewer studies provide insight into the analytical and biological sources of this variation. This is particularly true of chemical cytometry, in which individual cells are lysed and their contents separated, compared to more established single-cell measurements of the genome and transcriptome. To characterize population-level variation and its sources, we analyzed oxidative stress levels in 1278 individual Dictyostelium discoideum cells as a function of exogenous stress level and cell cycle position. Cells were exposed to varying levels of oxidative stress via singlet oxygen generation using the photosensitizer Rose Bengal. Single-cell data reproduced the dose-response observed in ensemble measurements by CE-LIF, superimposed with high levels of heterogeneity. Through experiments and data analysis, we explored possible biological sources of this heterogeneity. No trend was observed between population variation and oxidative stress level, but cell cycle position was a major contributor to heterogeneity in oxidative stress. Cells synchronized to the same stage of cell division were less heterogeneous than unsynchronized cells (RSD of 37-51% vs 93%), and mitotic cells had higher levels of reactive oxygen species than interphase cells. While past research has proposed changes in cell size during the cell cycle as a source of biological noise, the measurements presented here use an internal standard to normalize for effects of cell volume, suggesting a more complex contribution of cell cycle to heterogeneity of oxidative stress.

Sensing of H2O2-induced oxidative stress by the UPF factor complex is crucial for activation of catalase-3 expression in Neurospora

UPF-1-UPF-2-UPF-3 complex-orchestrated nonsense-mediated mRNA decay (NMD) is a well-characterized eukaryotic cellular surveillance mechanism that not only degrades aberrant transcripts to protect the integrity of the transcriptome but also eliminates normal transcripts to facilitate appropriate cellular responses to physiological and environmental changes. Here, we describe the multifaceted regulatory roles of the Neurospora crassa UPF complex in catalase-3 (cat-3) gene expression, which is essential for scavenging H2O2-induced oxidative stress. First, losing UPF proteins markedly slowed down the decay rate of cat-3 mRNA. Second, UPF proteins indirectly attenuated the transcriptional activity of cat-3 gene by boosting the decay of cpc-1 and ngf-1 mRNAs, which encode a well-studied transcription factor and a histone acetyltransferase, respectively. Further study showed that under oxidative stress condition, UPF proteins were degraded, followed by increased CPC-1 and NGF-1 activity, finally activating cat-3 expression to resist oxidative stress. Together, our data illustrate a sophisticated regulatory network of the cat-3 gene mediated by the UPF complex under physiological and H2O2-induced oxidative stress conditions.

A combined transcriptomic and physiological approach to understanding the adaptive mechanisms to cope with oxidative stress in Fusarium graminearum

In plant-pathogen interactions, oxidative bursts are crucial for plants to defend themselves against pathogen infections. Rapid production and accumulation of reactive oxygen species kill pathogens directly and cause local cell death, preventing pathogens from spreading to adjacent cells. Meanwhile, the pathogens have developed several mechanisms to tolerate oxidative stress and successfully colonize plant tissues. In this study, we investigated the mechanisms responsible for resistance to oxidative stress by analyzing the transcriptomes of six oxidative stress-sensitive strains of the plant pathogenic fungus Fusarium graminearum. Weighted gene co-expression network analysis identified several pathways related to oxidative stress responses, including the DNA repair system, autophagy, and ubiquitin-mediated proteolysis. We also identified hub genes with high intramodular connectivity in key modules and generated deletion or conditional suppression mutants. Phenotypic characterization of those mutants showed that the deletion of FgHGG4, FgHGG10, and FgHGG13 caused sensitivity to oxidative stress, and further investigation on those genes revealed that transcriptional elongation and DNA damage responses play roles in oxidative stress response and pathogenicity. The suppression of FgHGL7 also led to hypersensitivity to oxidative stress, and we demonstrated that FgHGL7 plays a crucial role in heme biosynthesis and is essential for peroxidase activity. This study increases the understanding of the adaptive mechanisms to cope with oxidative stress in plant pathogenic fungi. IMPORTANCE Fungal pathogens have evolved various mechanisms to overcome host-derived stresses for successful infection. Oxidative stress is a representative defense system induced by the host plant, and fungi have complex response systems to cope with it. Fusarium graminearum is one of the devastating plant pathogenic fungi, and understanding its pathosystem is crucial for disease control. In this study, we investigated adaptive mechanisms for coping with oxidative stress at the transcriptome level using oxidative stress-sensitive strains. In addition, by introducing genetic modification technique such as CRISPR-Cas9 and the conditional gene expression system, we identified pathways/genes required for resistance to oxidative stress and also for virulence. Overall, this study advances the understanding of the oxidative stress response and related mechanisms in plant pathogenic fungi.

Fe-Based Nanomaterials and Plant Growth Promoting Rhizobacteria Synergistically Degrade Polychlorinated Biphenyls by Producing Extracellular Reactive Oxygen Species

Plant growth promoting rhizobacteria (PGPR) produce extracellular reactive oxygen species (ROS) to protect plants from external stresses. Fe-based nanomaterials can potentially interact with PGPR and synergistically degrade organic pollutants, yet they have received no study. Here, we studied how the interaction between a typical PGPR (Pseudomonas chlororaphis, JD37) and Fe-based nanomaterials facilitated the degradation of 2,4,4'-trichlorobiphenyl (PCB28), by comparing the zerovalent iron of 20 nm (nZVI20), 100 nm (nZVI100), and 5 μm; iron oxide nanomaterials (α-Fe2O3, γ-Fe2O3, and Fe3O4) of ca. 20 nm; and ferrous and ferric salts. Although all Fe materials (0.1 g L-1) alone could not degrade aqueous PCB28 (0.1 mg L-1) under dark or aerobic conditions, nZVI20, nZVI100, α-Fe2O3, and Fe2+ promoted PCB28 degradation by JD37, with the half-life of PCB28 shortened from 16.5 h by JD37 alone to 8.1 h with nZVI100 cotreatment. Mechanistically, the nanomaterials stimulated JD37 to secrete phenazine-1-carboxylic acid and accelerated the NADH/NAD+ conversion, promoting O2*- generation; JD37 increased Fe(II) dissolution from the nanomaterials, facilitating *OH generation; and the ROS gradually degraded PCB28 into benzoic acid through dihydroxy substitution, oxidation to quinone, and Michael addition. These findings provide a new strategy of nanoenabled biodegradation of organic pollutants by applying Fe-based nanomaterials and PGPR.

Variations in amino acids caused by drought stress mediate the predisposition of Carya cathayensis to Botryosphaeria canker disease

Abiotic stresses can affect the outcome of plant-pathogen interactions, mostly by predisposing the host plant to infection; however, the crosstalk between pathogens and plants related to such predisposition remains unclear. Here, we investigated the predisposition of Carya cathayensis to infection by the fungal pathogen Botryosphaeria dothidea (Bd) caused by drought in the host plant. High levels of drought stress resulted in a significant increase in plant susceptibility to Bd. Drought significantly induced the accumulation of H2O2 and the free amino acids Pro, Leu, and Ile, and in the phloem tissues of plants, and decreased the content of non-structural carbohydrates. In vitro assays showed that Bd was sensitive to H2O2; however, Pro played a protective role against exogenous H2O2. Leu, Ile, and Pro induced asexual reproduction of Bd. Our results provide the first analysis of how drought predisposes C. cathayensis to Botrysphaeria canker via amino acid accumulation in the host plant, and we propose a model that integrates the plant-pathogen interactions involved.

Involvement of Bacterial and Fungal Extracellular Products in Transformation of Manganese-Bearing Minerals and Its Environmental Impact

Manganese oxides are considered an essential component of natural geochemical barriers due to their redox and sorptive reactivity towards essential and potentially toxic trace elements. Despite the perception that they are in a relatively stable phase, microorganisms can actively alter the prevailing conditions in their microenvironment and initiate the dissolution of minerals, a process that is governed by various direct (enzymatic) or indirect mechanisms. Microorganisms are also capable of precipitating the bioavailable manganese ions via redox transformations into biogenic minerals, including manganese oxides (e.g., low-crystalline birnessite) or oxalates. Microbially mediated transformation influences the (bio)geochemistry of manganese and also the environmental chemistry of elements intimately associated with its oxides. Therefore, the biodeterioration of manganese-bearing phases and the subsequent biologically induced precipitation of new biogenic minerals may inevitably and severely impact the environment. This review highlights and discusses the role of microbially induced or catalyzed processes that affect the transformation of manganese oxides in the environment as relevant to the function of geochemical barriers.

Revealing holistic metabolic responses associated with lipid and docosahexaenoic acid (DHA) production in Aurantiochytrium sp. SW1

Aurantiochytrium sp. SW1, a marine thraustochytrid, has been regarded as a potential candidate as a docosahexaenoic acid (DHA) producer. Even though the genomics of Aurantiochytrium sp. are available, the metabolic responses at a systems level are largely unknown. Therefore, this study aimed to investigate the global metabolic responses to DHA production in Aurantiochytrium sp. through transcriptome and genome-scale network-driven analysis. Of a total of 13,505 genes, 2527 differentially expressed genes (DEGs) were identified in Aurantiochytrium sp., unravelling the transcriptional regulations behinds lipid and DHA accumulation. The highest number of DEG were found for pairwise comparison between growth phase and lipid accumulating phase where a total of 1435 genes were down-regulated with 869 genes being up-regulated. These uncovered several metabolic pathways that contributing in DHA and lipid accumulation including amino acid and acetate metabolism which involve in the generation of crucial precursors. Upon applying network-driven analysis, hydrogen sulphide was found as potential reporter metabolite that could be associated with the genes related to acetyl-CoA synthesis for DHA production. Our findings suggest that the transcriptional regulation of these pathways is a ubiquitous feature in response to specific cultivation phases during DHA overproduction in Aurantiochytrium sp. SW1.

Hyphopodium-Specific Signaling Is Required for Plant Infection by Verticillium dahliae

For successful colonization, fungal pathogens have evolved specialized infection structures to overcome the barriers present in host plants. The morphology of infection structures and pathogenic mechanisms are diverse according to host specificity. Verticillium dahliae, a soil-borne phytopathogenic fungus, generates hyphopodium with a penetration peg on cotton roots while developing appressoria, that are typically associated with leaf infection on lettuce and fiber flax roots. In this study, we isolated the pathogenic fungus, V. dahliae (Vda^Sm), from Verticillium wilt eggplants and generated a GFP-labeled isolate to explore the colonization process of Vda^Sm on eggplants. We found that the formation of hyphopodium with penetration peg is crucial for the initial colonization of Vda^Sm on eggplant roots, indicating that the colonization processes on eggplant and cotton share a similar feature. Furthermore, we demonstrated that the VdNoxB/VdPls1-dependent Ca²⁺ elevation activating VdCrz1 signaling is a common genetic pathway to regulate infection-related development in V. dahliae. Our results indicated that VdNoxB/VdPls1-dependent pathway may be a desirable target to develop effective fungicides, to protect crops from V. dahliae infection by interrupting the formation of specialized infection structures.

The Molecular Chaperone Mechanism of the C-Terminal Domain of Large-Size Subunit Catalases

Large-size subunit catalases (LSCs) have an additional C-terminal domain (CT) that is structurally similar to Hsp31 and DJ-1 proteins, which have molecular chaperone activity. The CT of LSCs derives from a bacterial Hsp31 protein. There are two CT dimers with inverted symmetry in LSCs, one dimer in each pole of the homotetrameric structure. We previously demonstrated the molecular chaperone activity of the CT of LSCs. Like other chaperones, LSCs are abundant proteins that are induced under stress conditions and during cell differentiation in bacteria and fungi. Here, we analyze the mechanism of the CT of LSCs as an unfolding enzyme. The dimeric form of catalase-3 (CAT-3) CT (TDC3) of Neurospora crassa presented the highest activity as compared to its monomeric form. A variant of the CAT-3 CT lacking the last 17 amino acid residues (TDC3Δ17aa), a loop containing hydrophobic and charged amino acid residues only, lost most of its unfolding activity. Substituting charged for hydrophobic residues or vice versa in this C-terminal loop diminished the molecular chaperone activity in all the mutant variants analyzed, indicating that these amino acid residues play a relevant role in its unfolding activity. These data suggest that the general unfolding mechanism of CAT-3 CT involves a dimer with an inverted symmetry, and hydrophobic and charged amino acid residues. Each tetramer has four sites of interaction with partially unfolded or misfolded proteins. LSCs preserve their catalase activity under different stress conditions and, at the same time, function as unfolding enzymes.

Estimating the Vertical Ionization Potential of Single-Stranded DNA Molecules

The electronic properties of DNA molecules, defined by the sequence-dependent ionization potentials of nucleobases, enable long-range charge transport along the DNA stacks. This has been linked to a range of key physiological processes in the cells and to the triggering of nucleobase substitutions, some of which may cause diseases. To gain molecular-level understanding of the sequence dependence of these phenomena, we estimated the vertical ionization potential (vIP) of all possible nucleobase stacks in B-conformation, containing one to four Gua, Ade, Thy, Cyt, or methylated Cyt. To do this, we used quantum chemistry calculations and more precisely the second-order Møller-Plesset perturbation theory (MP2) and three double-hybrid density functional theory methods, combined with several basis sets for describing atomic orbitals. The calculated vIP of single nucleobases were compared to experimental data and those of nucleobase pairs, triplets, and quadruplets, to observed mutability frequencies in the human genome, reported to be correlated with vIP values. This comparison selected MP2 with the 6-31G* basis set as the best of the tested calculation levels. These results were exploited to set up a recursive model, called vIPer, which estimates the vIP of all possible single-stranded DNA sequences of any length based on the calculated vIPs of overlapping quadruplets. vIPer's vIP values correlate well with oxidation potentials measured by cyclic voltammetry and activities obtained through photoinduced DNA cleavage experiments, further validating our approach. vIPer is freely available on the github.com/3BioCompBio/vIPer repository.

Reactive oxygen species affect the potential for mineralization processes in permeable intertidal flats

Intertidal permeable sediments are crucial sites of organic matter remineralization. These sediments likely have a large capacity to produce reactive oxygen species (ROS) because of shifting oxic-anoxic interfaces and intense iron-sulfur cycling. Here, we show that high concentrations of the ROS hydrogen peroxide are present in intertidal sediments using microsensors, and chemiluminescent analysis on extracted porewater. We furthermore investigate the effect of ROS on potential rates of microbial degradation processes in intertidal surface sediments after transient oxygenation, using slurries that transitioned from oxic to anoxic conditions. Enzymatic removal of ROS strongly increases rates of aerobic respiration, sulfate reduction and hydrogen accumulation. We conclude that ROS are formed in sediments, and subsequently moderate microbial mineralization process rates. Although sulfate reduction is completely inhibited in the oxic period, it resumes immediately upon anoxia. This study demonstrates the strong effects of ROS and transient oxygenation on the biogeochemistry of intertidal sediments.

Potential of Alpha-(α)-Solanine as a Natural Inhibitor of Fungus Causing Leaf Spot Disease in Strawberry

Curvularia trifolii is an important pathogenic fungus that causes leaf spot disease in strawberry and other crops. Increased resistance in pathogenic fungi against chemical fungicides necessitates the search for biological alternatives to control plant fungal diseases. The present study aimed to perform transcriptome and metabolome analysis of C. trifolii fungi. We evaluated the potential of an alkaloid, namely alpha (α)-solanine, to inhibit the growth of Curvularia under in vitro conditions. Furthermore, transcriptomic and metabolomic analysis of treated C. trifolii was performed to identify the differential genes and metabolites. Results revealed that treatment with α-solanine resulted in the poor growth and development of fungal spores. The transcriptome analysis revealed that 1413 genes were differentially expressed (DEGs), among which 340 unigenes were up-regulated, 100 unigenes were down-regulated, and the rest were unaffected in treated samples. Gene ontology analysis revealed that the majority of the genes were related to oxidative stress in the fungus. Additionally, using ultra-high performance liquid chromatography-tandem mass spectrometry, we identified 455 metabolites, among which the majority of metabolites were related to lipid biosynthesis. The high number of genes related to lipid biosynthesis and reactive oxygen species revealed that α-solanine causes oxidative stress in Curvularia, leading to growth inhibition, and can be potentially used as an alternative to chemical fungicides.

Role of AtYap1 in the reactive oxygen species regulation of lovastatin production in Aspergillus terreus

Lovastatin has great medical and economic importance, and its production in Aspergillus terreus is positively regulated at transcriptional level, by reactive oxygen species (ROS) generated during idiophase. To investigate the role of the transcription factor Yap1 in the regulation of lovastatin biosynthesis by ROS, an orthologue of yap1 was identified in A. terreus TUB F-514 and knocked down (silenced) by RNAi. Results confirmed that the selected knockdown strain (Siyap1) showed decreased yap1 expression in both culture systems (submerged and solid-state fermentation). Transformants showed higher sensitivity to oxidative stress. Interestingly, knockdown mutant showed higher ROS levels in idiophase and an important increase in lovastatin production in submerged and solid-state fermentations: 60 and 70% increase, respectively. Furthermore, sporulation also increased by 600%. This suggested that AtYap1 was functioning as a negative regulator of the biosynthetic genes, and that lack of AtYap1 in the mutants would be derepressing these genes and could explain increased production. However, we have shown that lovastatin production is proportional to ROS levels, so ROS increase in the mutants alone could also be the cause of production increase. In this work, when ROS levels were decreased with antioxidant, to the levels shown by the parental strain, the lovastatin production and kinetics were similar to the ones of the parental strain. This means that AtYap1 does not regulate lovastatin biosynthetic genes, and that production increase observed in the knockdown strain was an indirect effect caused by ROS increase. This conclusion is compared with studies on other secondary metabolites produced by other fungal species. KEY POINTS: • ROS regulates lovastatin biosynthesis at transcriptional level, in solid-state, and in submerged fermentations. • ATyap1 knockdown mutants showed important lovastatin production increases (60 and 70%) and higher ROS levels. • When ROS were decreased in the silenced mutant to the parental strain's level, lovastatin kinetics were identical to the parental strain's.

The catalase-peroxidase PiCP1 plays a critical role in abiotic stress resistance, pathogenicity and asexual structure development in Phytophthora infestans

Catalase-peroxidase is a heme oxidoreductase widely distributed in bacteria and lower eukaryotes. In this study, we identified a catalase-peroxidase PiCP1 (PITG_05579) in Phytophthora infestans. PiCP1 had catalase/peroxidase and secretion activities and was highly expressed in sporangia and upregulated in response to oxidative and heat stresses. Compared with wild type, PiCP1-silenced transformants (STs) had decreased catalase activity, reduced oxidant stress resistance and damped cell wall integrity. In contrast, PiCP1-overexpression transformants (OTs) demonstrated increased tolerance to abiotic stresses and induced the upregulation of PR genes in the host salicylic acid pathway. The high concentration of PiCP1 can also induced callose deposition in plant tissue. Importantly, both STs and OTs have severely reduced sporangia formation and zoospore releasing rate, but the sporangia germination rate and type varied depending on environmental conditions. Comparative sequence analyses show that catalase-peroxidases are broadly distributed and highly conserved among soil-borne plant parasitic oomycetes, but not in freshwater-inhabiting or strictly plants-inhabiting oomycetes. In addition, we found that silencing PiCP1 downregulated the expression of PiCAT2. These results revealed the important roles of PiCP1 in abiotic stress resistance, pathogenicity and in regulating asexual structure development in response to environmental change. Our findings provide new insights into catalase-peroxidase functions in eukaryotic pathogens.

Direct observation of Mn distribution/speciation within and surrounding a basidiomycete fungus in the production of Mn-oxides important in toxic element containment

Biogenic manganese (Mn) oxides occur ubiquitously in the environment including the uranium (U) mill tailings at the Ningyo-toge U mine in Okayama, Japan, being important in the sequestration of radioactive radium. To understand the nanoscale processes in Mn oxides formation at the U mill tailings site, Mn²⁺ absorption by a basidiomycete fungus, Coprinopsis urticicola, isolated from Ningyo-toge mine water samples, was investigated in the laboratory under controlled conditions utilizing electron microscopy, synchrotron-based X-ray analysis, and fluorescence microscopy with a molecular pH probe. The fungus' growth was first investigated in an agar-solidified medium supplemented with 1.0 mmol/L Mn²⁺, and Cu²⁺ (0-200 μM), Zn²⁺ (0-200 μM), or diphenyleneiodonium (DPI) chloride (0-100 μM) at 25 °C. The results revealed that Zn²⁺ has no significant effects on Mn oxide formation, whereas Cu²⁺ and DPI significantly inhibit both fungal growth and Mn oxidation, indicating superoxide-mediated Mn oxidation. Indeed, nitroblue tetrazolium and diaminobenzidine assays on the growing fungus revealed the production of superoxide and peroxide. During the interaction of Mn²⁺ with the fungus in solution medium at the initial pH of 5.67, a small fraction of Mn²⁺ infiltrated the fungal hyphae within 8 h, forming a few tens of nm-sized concentrates of soluble Mn²⁺ in the intracellular pH of ∼6.5. After 1 day of incubation, Mn oxides began to precipitate on the hyphae, which were characterized as fibrous nanocrystals with a hexagonal birnessite-structure, these forming spherical aggregates with a diameter of ∼1.5 μm. These nanoscale processes associated with the fungal species derived from the Ningyo-toge mine area provide additional insights into the existing mechanisms of Mn oxidation by filamentous fungi at other U mill tailings sites under circumneutral pH conditions. Such processes add to the class of reactions important to the sequestration of toxic elements.

A lectin gene is involved in the defense of Pleurotus ostreatus against the mite predator Tyrophagus putrescentiae

The storage mite, Tyrophagus putrescentiae, found worldwide in many habitats, is an important pest of edible mushrooms. Excessive chemical spraying for pest control has been linked to environmental pollution, health risks, insecticide resistance development, and food safety. Host resistance can be sustainable and cost-effective and provide effective and economical pest control. Previous studies have reported that the oyster mushroom Pleurotus ostreatus has evolved effective defense mechanisms against T. putrescentiae attack, but the underlying mechanism remains unclear. Here we report that a lectin gene from P. ostreatus mycelia, Polec2, induced fungal resistance to mite grazing. Polec2 belongs to a galectin-like lectin classification, encoding a protein with β-sandwith-fold domain. Overexpression of Polec2 in P. ostreatus led to activation of the reactive oxygen species (ROS)/mitogen-activated protein kinases (MAPKs) signaling pathway, salicylic acid (SA), and jasmonate (JA) biosynthesis. The activation resulted in bursts of antioxidant activities of catalases (CAT), peroxidases (POD), superoxide dismutases (SOD), and increased production of SA, JA, jasmonic acid-isoleucine (JA-Ile) and jasmonic acid methyl ester (MeJA), accompanied by reduced T. putrescentiae feeding and suppressed its population. We also provide an overview of the phylogenetic distribution of lectins across 22 fungal genomes. Our findings shed light on the molecular mechanisms of P. ostreatus' defense against the mite predator and will be useful in investigating the molecular basis of fungi-fungivory interactions and gene mining for pest-resistance genes.

Light-independent anaerobic microbial oxidation of manganese driven by an electrosyntrophic coculture

Anaerobic microbial manganese oxidation (AMMO) has been considered an ancient biological metabolism for Mn element cycling on Archaean Earth before the presence of oxygen. A light-dependent AMMO was recently observed under strictly anoxic conditions, providing a new proxy for the interpretation of the evolution of oxygenic photosynthesis. However, the feasibility of biotic Mn(II) oxidation in dark geological habitats that must have been abundant remains unknown. Therefore, we discovered that it would be possible to achieve AMMO in a light-independent electrosyntrophic coculture between Rhodopseudomonas palustris and Geobacter metallireducens. Transmission electron microscopy analysis revealed insoluble particle formation in the coculture with Mn(II) addition. X-ray diffraction and X-ray photoelectron spectroscopy analysis verified that these particles were a mixture of MnO2 and Mn3O4. The absence of Mn oxides in either of the monocultures indicated that the Mn(II)-oxidizing activity was induced via electrosyntrophic interactions. Radical quenching and isotopic experiments demonstrated that hydroxyl radicals (•OH) produced from H2O dissociation by R. palustris in the coculture contributed to Mn(II) oxidation. All these findings suggest a new, symbiosis-dependent and light-independent AMMO route, with potential importance to the evolution of oxygenic photosynthesis and the biogeochemical cycling of manganese on Archaean and modern Earth.

Catalases in the pathogenesis of Sporothrix schenckii research

Pathogenic fungal infection success depends on the ability to escape the immune response. Most strategies for fungal infection control are focused on the inhibition of virulence factors and increasing the effectiveness of antifungal drugs. Nevertheless, little attention has been focused on their physiological resistance to the host immune system. Hints may be found in pathogenic fungi that also inhabit the soil. In nature, the saprophyte lifestyle of fungi is also associated with predators that can induce oxidative stress upon cell damage. The natural sources of nutrients for fungi are linked to cellulose degradation, which in turn generates reactive oxygen species (ROS). Overall, the antioxidant arsenal needed to thrive both in free-living and pathogenic lifestyles in fungi is fundamental for success. In this review, we present recent findings regarding catalases and oxidative stress in fungi and how these can be in close relationship with pathogenesis. Additionally, special focus is placed on catalases of Sporothrix schenckii as a pathogenic model with a dual lifestyle. It is assumed that catalase expression is activated upon exposure to H₂O₂, but there are reports where this is not always the case. Additionally, it may be relevant to consider the role of catalases in S. schenckii survival in the saprophytic lifestyle and why their study can assess their involvement in the survival and therefore, in the virulence phenotype of different species of Sporothrix and when each of the three catalases are required. Also, studying antioxidant mechanisms in other isolates of pathogenic and free-living fungi may be linked to the virulence phenotype and be potential therapeutic and diagnostic targets. Thus, the rationale for this review to place focus on fungal catalases and their role in pathogenesis in addition to counteracting the effect of immune system reactive oxygen species. Fungi that thrive in soil and have mammal hosts could shed light on the importance of these enzymes in the two types of lifestyles. We look forward to encouraging more research in a myriad of areas on catalase biology with a focus on basic and applied objectives and placing these enzymes as virulence determinants.

Effects of M. oleifera leaf extract on the growth, physiological response and related immune gene expression of crucian carp fingerlings under Aeromonas hydrophila infection

We evaluated the effect of dietary supplementation with Moringa oleifera leaf extract on the resistance to Aeromonas hydrophila infection in crucian carp. The fish were randomly divided into five groups: the basal diet, the basal diet supplied with 0.25% (0.25 M), 0.5% (0.5 M), 0.75% (0.75 M) and 1.0% M. oleifera leaf extract (1.0 M) for 8 weeks. The growth, antioxidant capabilities, related immune genes as well as resistance to A. hydrophila infection were determined. The results showed that compared with the control group, the weight gain, specific growth rate in the group of 0.5% M. oleifera leaf extract, serum superoxide dismutase (SOD), albumin (ALB) and glutathione peroxidase (GSH-Px), the gene expression of hepatopancreas BTB and CNC homolog 1 (Bach1), NF-E2-related factor 2 (Nrf2), peroxidases (PRX) and NADPH oxidase (NOX) in the group of 0.5%-1.0% M. oleifera leaf extract increased, while feed conversion ratio, serum cortisol, red blood cell (RBC), alanine aminotransferase (ALT), malonaldehyde (MDA) decreased in the group of 0.5%-1.0% M. oleifera leaf extract before the stress. After the infection, the group of 0.5% or 0.75% M. oleifera leaf extract also could improve the serum ALB, hepatopancreas Kelch-like-ECH-associated protein 1 (Keap1), Bach1, Nrf2, TOR, PRX and NOX and reduce cortisol compared with the control group. In summary, this study suggested that 0.5% M. oleifera leaf extract inclusion increased the growth performance, even had positive effects on physiological and immune function, and enhanced resistance against pathogenic infections in crucian carp. The optimum level of M. oleifera leaf extract for crucian carp was estimated to be 0.35%-0.48% based on polynomial comparison with FCR and SGR.

Glutamine Synthetase Contributes to the Regulation of Growth, Conidiation, Sclerotia Development, and Resistance to Oxidative Stress in the Fungus Aspergillus flavus

The basic biological function of glutamine synthetase (Gs) is to catalyze the conversion of ammonium and glutamate to glutamine. This synthetase also performs other biological functions. However, the roles of Gs in fungi, especially in filamentous fungi, are not fully understood. Here, we found that conditional disruption of glutamine synthetase (AflGsA) gene expression in Aspergillus flavus by using a xylose promoter leads to a complete glutamine deficiency. Supplementation of glutamine could restore the nutritional deficiency caused by AflGsA expression deficiency. Additionally, by using the xylose promoter for the downregulation of AflgsA expression, we found that AflGsA regulates spore and sclerotic development by regulating the transcriptional levels of sporulation genes abaA and brlA and the sclerotic generation genes nsdC and nsdD, respectively. In addition, AflGsA was found to maintain the balance of reactive oxygen species (ROS) and to aid in resisting oxidative stress. AflGsA is also involved in the regulation of light signals through the production of glutamine. The results also showed that the recombinant AflGsA had glutamine synthetase activity in vitro and required the assistance of metal ions. The inhibitor molecule L-α-aminoadipic acid suppressed the activity of rAflGsA in vitro and disrupted the morphogenesis of spores, sclerotia, and colonies in A. flavus. These results provide a mechanistic link between nutrition metabolism and glutamine synthetase in A. flavus and suggest a strategy for the prevention of fungal infection.

The Development of New Nanocomposite Polytetrafluoroethylene/Fe2O3 NPs to Prevent Bacterial Contamination in Meat Industry

The bacterial contamination of cutting boards and other equipment in the meat processing industry is one of the key reasons for reducing the shelf life and consumer properties of products. There are two ways to solve this problem. The first option is to create coatings with increased strength in order to prevent the formation of micro damages that are favorable for bacterial growth. The second possibility is to create materials with antimicrobial properties. The use of polytetrafluoroethylene (PTFE) coatings with the addition of metal oxide nanoparticles will allow to the achieving of both strength and bacteriostatic effects at the same time. In the present study, a new coating based on PTFE and Fe₂O₃ nanoparticles was developed. Fe₂O₃ nanoparticles were synthesized by laser ablation in water and transferred into acetone using the developed procedures. An acetone-based colloidal solution was mixed with a PTFE-based varnish. Composites with concentrations of Fe₂O₃ nanoparticles from 0.001-0.1% were synthesized. We studied the effect of the obtained material on the generation of ROS (hydrogen peroxide and hydroxyl radicals), 8-oxoguanine, and long-lived active forms of proteins. It was found that PTFE did not affect the generation of all the studied compounds, and the addition of Fe₂O₃ nanoparticles increased the generation of H₂O₂ and hydroxyl radicals by up to 6 and 7 times, respectively. The generation of 8-oxoguanine and long-lived reactive protein species in the presence of PTFE/Fe₂O₃ NPs at 0.1% increased by 2 and 3 times, respectively. The bacteriostatic and cytotoxic effects of the developed material were studied. PTFE with the addition of Fe₂O₃ nanoparticles, at a concentration of 0.001% or more, inhibited the growth of E. coli by 2-5 times compared to the control or PTFE without NPs. At the same time, PTFE, even with the addition of 0.1% Fe₂O₃ nanoparticles, did not significantly impact the survival of eukaryotic cells. It was assumed that the resulting composite material could be used to cover cutting boards and other polymeric surfaces in the meat processing industry.

Monofunctional Heme-Catalases

The review focuses on four issues that are critical for the understanding of monofunctional catalases. How hydrogen peroxide (H2O2) reaches the active site and outcompetes water molecules to be able to function at a very high rate is one of the issues examined. Part of the answer is a gate valve system that is instrumental to drive out solvent molecules from the final section of the main channel. A second issue relates to how the enzyme deals with an unproductive reactive compound I (Cpd I) intermediate. Peroxidatic two and one electron donors and the transfer of electrons to the active site from NADPH and other compounds are reviewed. The new ascribed catalase reactions are revised, indicating possible measurement pitfalls. A third issue concerns the heme b to heme d oxidation, why this reaction occurs only in some large-size subunit catalases (LSCs), and the possible role of singlet oxygen in this and other modifications. The formation of a covalent bond between the proximal tyrosine with the vicinal residue is analyzed. The last issue refers to the origin and function of the additional C-terminal domain (TD) of LSCs. The TD has a molecular chaperone activity that is traced to a gene fusion between a Hsp31-type chaperone and a small-size subunit catalase (SSC).

Dissolved and particulate iron redox speciation during the LOHAFEX fertilization experiment

The redox speciation of iron was determined during the iron fertilization LOHAFEX and for the first time, the chemiluminescence assay of filtered and unfiltered samples was systematically compared. We hypothesize that higher chemiluminescence in unfiltered samples was caused by Fe(II) adsorbed onto biological particles. Dissolved and particulate Fe(II) increased in the mixed layer steadily 6-fold during the first two weeks and decreased back to initial levels by the end of LOHAFEX. Both Fe(II) forms did not show diel cycles downplaying the role of photoreduction. The chemiluminescence of unfiltered samples across the patch boundaries showed strong gradients, correlated significantly to biomass and the photosynthetic efficiency and were higher at night, indicative of a biological control. At 150 m deep, a secondary maximum of dissolved Fe(II) was associated with maxima of nitrite and ammonium despite high oxygen concentrations. We hypothesize that during LOHAFEX, iron redox speciation was mostly regulated by trophic interactions.

Possible Synergies of Nanomaterial-Assisted Tissue Regeneration in Plasma Medicine: Mechanisms and Safety Concerns

Cold atmospheric plasma and nanomedicine originally emerged as individual domains, but are increasingly applied in combination with each other. Most research is performed in the context of cancer treatment, with only little focus yet on the possible synergies. Many questions remain on the potential of this promising hybrid technology, particularly regarding regenerative medicine and tissue engineering. In this perspective article, we therefore start from the fundamental mechanisms in the individual technologies, in order to envision possible synergies for wound healing and tissue recovery, as well as research strategies to discover and optimize them. Among these strategies, we demonstrate how cold plasmas and nanomaterials can enhance each other's strengths and overcome each other's limitations. The parallels with cancer research, biotechnology and plasma surface modification further serve as inspiration for the envisioned synergies in tissue regeneration. The discovery and optimization of synergies may also be realized based on a profound understanding of the underlying redox- and field-related biological processes. Finally, we emphasize the toxicity concerns in plasma and nanomedicine, which may be partly remediated by their combination, but also partly amplified. A widespread use of standardized protocols and materials is therefore strongly recommended, to ensure both a fast and safe clinical implementation.

H2O2 Induces Calcium and ERMES Complex-Dependent Mitochondrial Constriction and Division as Well as Mitochondrial Outer Membrane Remodeling in Aspergillus nidulans

The dynamin-like protein DnmA and its receptor FisA are essential for H₂O₂-induced mitochondrial division in Aspergillus nidulans. Here, we show that in the absence of DnmA or FisA, mitochondria show few spontaneous transient constrictions, the frequency of which is extensively increased by H₂O₂ or the carbonyl cyanide m-chlorophenyl hydrazone (CCCP). While H₂O₂-induced constrictions are transient, CCCP induces a drastic and irreversible alteration of mitochondrial filaments. H₂O₂ induces a gradual mitochondrial depolarization, while CCCP-induced depolarization is abrupt. The calcium chelator BAPTA-AM prevents the formation of mitochondrial constrictions induced by either H₂O₂ or CCCP. H₂O₂ also induces major rearrangements of the mitochondrial outer membrane, which remain after constrictions dissipate, as well as changes in endoplasmic reticulum (ER) and nuclear morphology. Similar mitochondrial constriction, ER and nuclear morphology changes are detected during the early stages of asexual development. ER and ER-Mitochondria encounter structure (ERMES) complex—composed of proteins Mdm10, Mmm1, Mdm43 and Mdm12—are important for mitochondrial division in Saccharomyces cerevisiae. As the Mdm10 ortholog MdmB was found to be essential in A. nidulans, we evaluated its functions in ΔmdmB terminal mutants and ΔmdmB heterokaryons. ΔmdmB conidia produce a short germ tube that fails to grow further, in which inherited mitochondria become gigantic and round shaped, lacking clear contacts with the ER. In slow-growing ΔmdmB heterokaryotic mycelia, multiple hyphae contain very long mitochondria with high ROS levels, as occur in ΔdnmA and ΔfisA mutants. In this hyphae, H₂O₂ fails to induce mitochondrial constrictions but not outer mitochondrial membrane reshaping, indicating that these are two separate effects of H₂O₂. Our results indicate that H₂O₂ induces a generalized mitochondrial constriction response, prior to actual division, involving gradual depolarization; they also indicate that Ca²⁺ and the ERMES complex are critical for both mitochondrial constriction and division. This supports a view of mitochondrial dynamics as the result of a cascade of signaling events that can be initiated in vivo by H₂O₂.

Antimicrobial Mechanism and Secondary Metabolite Profiles of Biocontrol Agent Streptomyces lydicus M01 Based on Ultra-High-Performance Liquid Chromatography Connected to a Quadrupole Time-of-Flight Mass Spectrometer Analysis and Genome Sequencing

Streptomyces lydicus was used as biopesticide for crop protection in agriculture, however, the antimicrobial mechanism remains unclear and no systematic research on the secondary metabolites of S. lydicus has been reported. In this study, the extract of S. lydicus M01 culture was used to treat plant pathogen Alternaria alternata and morphological changes in the plasma membrane and cell wall of hyphae and conidia were observed. Fluorescence microscopy combined with different dyes showed that the accumulation of reactive oxygen species and cell death were also induced. To investigate the secondary metabolites in the culture filtrate, an online detection strategy of ultra-high-performance liquid chromatography connected to a quadrupole time-of-flight mass spectrometer (UPLC-Q-TOF-MS) was used for identification. The results revealed an excess of 120 metabolites, mainly consisted of fungicides, antibacterial agents, herbicides, insecticides, and plant growth regulators, such as IAA. Among which the five dominant components were oxadixyl, chloreturon, S-metolachlor, fentrazamide, and bucarpolate. On the other hand, the complete genome of S. lydicus M01 was sequenced and a number of key function gene clusters that contribute to the biosynthesis of active secondary metabolites were revealed. This is the first systematic characterization of S. lydicus secondary metabolites, and these results offer novel and valuable evidence for a comprehensive understanding of the biocontrol agent S. lydicus and its application in agriculture.

ClNOX1/ClNOXR-mediated MAPK and cAMP-PKA signalling pathways and ROS metabolism are involved in Curvularia lunata sexual reproduction and host infection

NADPH oxidases (NOXs) and hydrogen peroxide (H₂ O₂ ) are involved in physiological and pathological processes, and cell fate decisions in organisms. However, regulatory mechanism of NOXs and the role of H₂ O₂ on fungal sexual reproduction and host infection remain largely unexplored. Here, we identified ROS metabolic genes and key signalling genes of MAPK and cAMP-PKA pathways in Curvularia lunata, which were NOX ClNOX1 and ClNOXR, superoxide dismutase ClSOD1 and catalase ClCAT4, redox-regulated transcription factor ClAP1, Ras small GTPases Clg2P, pheromone-response MAPK ClK1 and cAMP-PKA ClSCHA, and characterized the functions of these genes. The results showed that ClNOX1 localized to the plasma membrane. ClNOX1 and ClNOXR were involved in sexual reproduction and host infection via ClNOX1/ClNOXR-derived H₂ O₂ as well as MAPK and cAMP-PKA signalling pathways. H₂ O₂ acted as a signalling molecule to regulate sexual reproduction and host infection in C. lunata.

Large-Size Subunit Catalases Are Chimeric Proteins: A H2O2 Selecting Domain with Catalase Activity Fused to a Hsp31-Derived Domain Conferring Protein Stability and Chaperone Activity

Bacterial and fungal large-size subunit catalases (LSCs) are like small-size subunit catalases (SSCs) but have an additional C-terminal domain (CT). The catalytic domain is conserved at both primary sequence and structural levels and its amino acid composition is optimized to select H₂O₂ over water. The CT is structurally conserved, has an amino acid composition similar to very stable proteins, confers high stability to LSCs, and has independent molecular chaperone activity. While heat and denaturing agents increased Neurospora crassa catalase-1 (CAT-1) activity, a CAT-1 version lacking the CT (C63) was no longer activated by these agents. The addition of catalase-3 (CAT-3) CT to the CAT-1 or CAT-3 catalase domains prevented their heat denaturation in vitro. Protein structural alignments indicated CT similarity with members of the DJ-1/PfpI superfamily and the CT dimers present in LSCs constitute a new type of symmetric dimer within this superfamily. However, only the bacterial Hsp31 proteins show sequence similarity to the bacterial and fungal catalase mobile coil (MC) and are phylogenetically related to MC_CT sequences. LSCs might have originated by fusion of SSC and Hsp31 encoding genes during early bacterial diversification, conferring at the same time great stability and molecular chaperone activity to the novel catalases.

bZIP transcription factors PcYap1 and PcRsmA link oxidative stress response to secondary metabolism and development in Penicillium chrysogenum

Background

Reactive oxygen species (ROS) trigger different morphogenic processes in filamentous fungi and have been shown to play a role in the regulation of the biosynthesis of some secondary metabolites. Some bZIP transcription factors, such as Yap1, AtfA and AtfB, mediate resistance to oxidative stress and have a role in secondary metabolism regulation. In this work we aimed to get insight into the molecular basis of this regulation in the industrially important fungus Penicillium chrysogenum through the characterization of the role played by two effectors that mediate the oxidative stress response in development and secondary metabolism.

Results

In P. chrysogenum, penicillin biosynthesis and conidiation are stimulated by the addition of H2O2 to the culture medium, and this effect is mediated by the bZIP transcription factors PcYap1 and PcRsmA. Silencing of expression of both proteins by RNAi resulted in similar phenotypes, characterized by increased levels of ROS in the cell, reduced conidiation, higher sensitivity of conidia to H2O2 and a decrease in penicillin production. Both PcYap1 and PcRsmA are able to sense H2O2-generated ROS in vitro and change its conformation in response to this stimulus. PcYap1 and PcRsmA positively regulate the expression of brlA, the first gene of the conidiation central regulatory pathway. PcYap1 binds in vitro to a previously identified regulatory sequence in the promoter of the penicillin gene pcbAB: TTAGTAA, and to a TTACTAA sequence in the promoter of the brlA gene, whereas PcRsmA binds to the sequences TGAGACA and TTACGTAA (CRE motif) in the promoters of the pcbAB and penDE genes, respectively.

Conclusions

bZIP transcription factors PcYap1 and PcRsmA respond to the presence of H2O2-generated ROS and regulate oxidative stress response in the cell. Both proteins mediate ROS regulation of penicillin biosynthesis and conidiation by binding to specific regulatory elements in the promoters of key genes. PcYap1 is identified as the previously proposed transcription factor PTA1 (Penicillin Transcriptional Activator 1), which binds to the regulatory sequence TTAGTAA in the pcbAB gene promoter. This is the first report of a Yap1 protein directly regulating transcription of a secondary metabolism gene. A model describing the regulatory network mediated by PcYap1 and PcRsmA is proposed.

NADPH Oxidase Gene, FgNoxD, Plays a Critical Role in Development and Virulence in Fusarium graminearum

NADPH oxidase is an enzyme that generates reactive oxygen species from oxygen and NADPH and is highly conserved in eukaryotes. In Fusarium graminearum, a series of different Nox enzymes have been identified. NoxA is involved in sexual development and ascospore production and, like NoxB, also contributes to pathogenicity. Both NoxA and NoxB are regulated by the subunit NoxR, whereas NoxC is usually self-regulated by EF-hand motifs found on the enzyme. In this study, we characterized another NADPH oxidase in F. graminearum, FgNoxD. In the FgNoxD deletion mutant, vegetative growth and conidia production were reduced, while sexual development was totally abolished. The FgNoxD deletion mutant also showed reduced resistance to cell wall perturbing agents; cell membrane inhibitors; and osmotic, fungicide, cold, and extracellular oxidative stress, when compared to the wild type. Moreover, in comparison to the wild type, the FgNoxD deletion mutant exhibited reduced virulence against the host plant. The FgNoxD deletion mutant produced less deoxynivalenol than the wild type, and the Tri5 and Tri6 gene expression was also downregulated. In conclusion, our findings show that FgNoxD is involved in the survival against various stresses, conidiation, sexual development, and virulence, highlighting this enzyme as a new target to control the disease caused by F. graminearum.

Development of a Deep-Sea Submersible Chemiluminescent Analyzer for Sensing Short-Lived Reactive Chemicals

Based on knowledge of their production pathways, and limited discrete observations, a variety of short-lived chemical species are inferred to play active roles in chemical cycling in the sea. In some cases, these species may exert a disproportionate impact on marine biogeochemical cycles, affecting the redox state of metal and carbon, and influencing the interaction between organisms and their environment. One such short-lived chemical is superoxide, a reactive oxygen species (ROS), which undergoes a wide range of environmentally important reactions. Yet, due to its fleeting existence which precludes traditional shipboard analyses, superoxide concentrations have never been characterized in the deep sea. To this end, we have developed a submersible oceanic chemiluminescent analyzer of reactive intermediate species (SOLARIS) to enable continuous measurements of superoxide at depth. Fluidic pumps on SOLARIS combine seawater for analysis with reagents in a spiral mixing cell, initiating a chemiluminescent reaction that is monitored by a photomultiplier tube. The superoxide in seawater is then related to the quantity of light produced. Initial field deployments of SOLARIS have revealed high-resolution trends in superoxide throughout the water column. SOLARIS presents the opportunity to constrain the distributions of superoxide, and any number of chemiluminescent species in previously unexplored environments.

Fungal-Mineral Interactions Modulating Intrinsic Peroxidase-like Activity of Iron Nanoparticles: Implications for the Biogeochemical Cycles of Nutrient Elements and Attenuation of Contaminants

Fungal-mediated extracellular reactive oxygen species (ROS) are essential for biogeochemical cycles of carbon, nitrogen, and contaminants in terrestrial environments. These ROS levels may be modulated by iron nanoparticles that possess intrinsic peroxidase (POD)-like activity (nanozymes). However, it remains largely undescribed how fungi modulate the POD-like activity of the iron nanoparticles with various crystallinities and crystal facets. Using well-controlled fungal-mineral cultivation experiments, here, we showed that fungi possessed a robust defect engineering strategy to modulate the POD-like activity of the attached iron minerals by decreasing the catalytic activity of poorly ordered ferrihydrite but enhancing that of well-crystallized hematite. The dynamics of POD-like activity were found to reside in molecular trade-offs between lattice oxygen and oxygen vacancies in the iron nanoparticles, which may be located in a cytoprotective fungal exoskeleton. Together, our findings unveil coupled POD-like activity and oxygen redox dynamics during fungal-mineral interactions, which increase the understanding of the catalytic mechanisms of POD-like nanozymes and microbial-mediated biogeochemical cycles of nutrient elements as well as the attenuation of contaminants in terrestrial environments.

Coupled Mn(II) and Cr(III) Oxidation Mediated by Ascomycete Fungi

Manganese (Mn) oxides are considered as the primary oxidant of trivalent chromium [Cr(III)] in the environment. Microbial activities are responsible for the majority of Mn oxide formation in nature, thus likely influencing Cr(III) oxidation. Previous studies have been limited to Cr(III) oxidation by bacterial Mn oxides. Herein, we report coupled Mn(II) and Cr(III) oxidation in the presence of three Mn(II)-oxidizing Ascomycete fungi. In contrast to the previously reported inhibitory effect of Cr(III) on bacterial Mn(II) oxidation, varying effects of Cr(III) on fungal Mn(II) oxidation were observed, which may be linked to their Mn(II)-oxidation mechanisms. Under the concentrations of Mn(II) and Cr(III) applied in this study, Cr(III) promoted Mn(II) oxidation if it was mediated by hyphae-associated processes, but inhibited Mn(II) oxidation if it was achieved via extracellular enzymes/metabolites. The Cr(III) oxidation rate and extent were affected by Cr(III) speciation, Cr(VI) removal capacity (i.e., adsorption/reduction) of fungi, and organic content. The morphology and spatial relationship of Mn oxides with fungi varied, depending on fungal species and Cr(III) presence. Our findings highlight the importance of Mn(II)-oxidizing fungi in biogeochemical cycles of Mn and Cr and have significant implications for the origin of geogenic Cr(VI) and stability of reduced chromium in contaminated environments.

Effects and interactions of metal oxides in microparticle-enhanced cultivation of filamentous microorganisms

Filamentous microorganisms are used as molecular factories in industrial biotechnology. In 2007, a new approach to improve productivity in submerged cultivation was introduced: microparticle-enhanced cultivation (MPEC). Since then, numerous studies have investigated the influence of microparticles on the cultivation. Most studies considered MPEC a morphology engineering approach, in which altered morphology results in increased productivity. But sometimes similar morphological changes lead to decreased productivity, suggesting that this hypothesis is not a sufficient explanation for the effects of microparticles. Effects of surface chemistry on particles were paid little attention, as particles were often considered chemically-inert and bioinert. However, metal oxide particles strongly interact with their environment. This review links morphological, physical, and chemical properties of microparticles with effects on culture broth, filamentous morphology, and molecular biology. More precisely, surface chemistry effects of metal oxide particles lead to ion leaching, adsorption of enzymes, and generation of reactive oxygen species. Therefore, microparticles interfere with gene regulation, metabolism, and activity of enzymes. To enhance the understanding of microparticle-based morphology engineering, further interactions between particles and cells are elaborated. The presented description of phenomena occurring in MPEC eases the targeted choice of microparticles, and thus, contributes to improving the productivity of microbial cultivation technology.

Microalgae-Derived Health Supplements to Therapeutic Shifts: Redox-Based Study Opportunities with AIE-Based Technologies

Reactive oxygen species (ROS) are highly reactive molecules, serve the normal signaling in different cell types. Targeting ROS as the chemical signals, different stress based strategies have been developed to synthesis different anti-inflammatory molecules in microalgae. These molecules could be utilized as health supplements in human. To provoke the ROS-mediated defence systems, their connotation with the associated conditions must be well understood, therefore, proper tools for studying ROS in natural state are essential. The in vivo detection of ROS with phosphorescent probes offers promising opportunities to study these molecules in a non-invasive manner. Most of the common problems in the traditional fluorescent probes are lower photostability, excitation intensity, slow responsiveness, and the microenvironment that challenge their performance. Some ROS-specific aggregationinduced emission luminogens (AIEgens) with pronounced spatial and temporal resolution have recently demonstrated high selectivity, rapid responsiveness, and efficacies to resolve the aggregation-caused quenching issues. The nanocomposites of some AIE-photosensitizers can also improve the ROS-mediated photodynamic therapy. These AIEgens could be used to induce bioactive components in microalgae through altering the ROS signaling, therefore are more auspicious for biomedical research. This study reviews the prospects of AIEgen-based technologies to understand the ROS mediated bio-physiological processes in microalgae for better healthcare benefits.

Sclerotinia sclerotiorum Thioredoxin1 (SsTrx1) is required for pathogenicity and oxidative stress tolerance

Sclerotinia sclerotiorum infects host plant tissues by inducing necrosis to source nutrients needed for its establishment. Tissue necrosis results from an enhanced generation of reactive oxygen species (ROS) at the site of infection and apoptosis. Pathogens have evolved ROS scavenging mechanisms to withstand host-induced oxidative damage. However, the genes associated with ROS scavenging pathways are yet to be fully investigated in S. sclerotiorum. We selected the S. sclerotiorum Thioredoxin1 gene (SsTrx1) for our investigations as its expression is significantly induced during S. sclerotiorum infection. RNA interference-induced silencing of SsTrx1 in S. sclerotiorum affected the hyphal growth rate, mycelial morphology, and sclerotial development under in vitro conditions. These outcomes confirmed the involvement of SsTrx1 in promoting pathogenicity and oxidative stress tolerance of S. sclerotiorum. We next constructed an SsTrx1-based host-induced gene silencing (HIGS) vector and mobilized it into Arabidopsis thaliana (HIGS-A) and Nicotiana benthamiana (HIGS-N). The disease resistance analysis revealed significantly reduced pathogenicity and disease progression in the transformed genotypes as compared to the nontransformed and empty vector controls. The relative gene expression of SsTrx1 increased under oxidative stress. Taken together, our results show that normal expression of SsTrx1 is crucial for pathogenicity and oxidative stress tolerance of S. sclerotiorum.