Saprophytic Soil Fungi Research Articles

The changes of chemical molecular components in soil organic matter are associated with fungus Mortierella capitata K.

Fungi play essential roles in the turnover of soil organic matter (SOM). However, it is unclear how fungi affect the chemical molecular composition of SOM. This study examined the effect of saprophytic soil fungus Mortierella capitata K on different soil carbon components and their molecular components. Genome sequencing revealed the ability of the strain to synthesize and degrade heterocycles, heteropolysaccharides, alkenes, terpenoids, steroids, amides, lipids, and amino acids. Subsequently, the turnover of SOM in M. capitata K inoculation with straw (KS) or without straw (K) addition was investigated via an aseptic microcosm experiment for 240 days. Pyrolysis gas chromatography-mass spectrometry analysis (Py-GCMS) showed that the molecular composition of SOM significantly changed with culture time in the two treatments. M. capitata K inoculation increased the relative abundance of tetradecanentitrile, dotriacontane, n-hexadecanoic acid, and n-dodecyl methacrylate in SOM during day 5–180. In contrast, the proportion of components in SOM (oxidizable by potassium permanganate) reduced after M. capitata K inoculation. Similarly, M. capitata K inoculation decreased the relative abundance of alkanes, alkenes, and alcohols in the original SOM on the 240th day. However, the above decline was effectively alleviated after straw addition. Straw addition significantly improved the abundance of n-hexadecanoic acid. RNA sequencing on the 30th day revealed the association between genes encoding alcohol dehydrogenase and SOM ester formation. Therefore, this study may provide insights into the complex feedback loops between microbial activities and molecular composition changes in SOM.

Differential Expression of Genes Related to Growth and Aflatoxin Synthesis in Aspergillus flavus When Inhibited by Bacillus velezensis Strain B2.

Aspergillus flavus is a saprophytic soil fungus that infects and contaminates seed crops with the highly carcinogenic aflatoxin, which brings health hazards to animals and humans. In this study, bacterial strains B1 and B2 isolated from the rhizosphere soil of camellia sinensis had significant antagonistic activities against A. flavus. Based on the phylogenetic analysis of 16SrDNA gene sequence, bacterial strains B1 and B2 were identified as Bacillus tequilensis and Bacillus velezensis, respectively. In addition, the transcriptome analysis showed that some genes related to A. flavus growth and aflatoxin synthesis were differential expressed and 16 genes in the aflatoxin synthesis gene cluster showed down-regulation trends when inhibited by Bacillus velezensis strain B2. We guessed that the Bacillus velezensis strain B2 may secrete some secondary metabolites, which regulate the related gene transcription of A. flavus to inhibit growth and aflatoxin production. In summary, this work provided the foundation for the more effective biocontrol of A. flavus infection and aflatoxin contamination by the determination of differential expression of genes related to growth and aflatoxin synthesis in A. flavus when inhibited by B. velezensis strain B2.

Exogenous Iron Induces NADPH Oxidases-Dependent Ferroptosis in the Conidia of Aspergillus flavus.

Aspergillus flavus is saprophytic soil fungus that contaminates seed crops with the carcinogenic secondary metabolite aflatoxin, posing a significant threat to humans and animals. Ferrous sulfate is a common iron supplement that is used to the treatment of iron-deficiency anemia. Here, we identified an unexpected inhibitory role of ferrous sulfate on A. flavus. With specific fluorescent dyes, we detected several conidial ferroptosis hallmarks in conidia under the treatment of 1 mM Fe2+, including nonapoptosis necrosis, iron-dependent, lipid peroxide accumulation, and ROS burst. However, unlike traditional ferroptosis in mammals, Fe2+ triggered conidial ferroptosis in A. flavus was regulated by NADPH oxidase (NOXs) activation instead of Fenton reaction. Transcriptomic and some other bioinformatics analyses showed that NoxA in A. flavus might be a potential target of Fe2+, and thus led to the occurrence of conidial ferroptosis. Furthermore, noxA deletion mutant was constructed, and both ROS generation and conidial ferroptosis in ΔnoxA was reduced when exposed to Fe2+. Taken together, our study revealed an exogenous Fe2+-triggered conidial ferroptosis pathway mediated by NoxA of A. flavus, which greatly contributes to the development of an alternative strategy to control this pathogen.

Cultivable soil fungi community response to agricultural management and tillage system on temperate soil

In agricultural soils, fungi constitute most of the total microbial biomass in the environment contributing with more than 50% of the soil biomass. The fungi should be considered as a link in the production not only by their attributes but also for their potential pathogenicity on crops chains. We aim to determine in what extent the combination of management styles and tillage systems control specific cultivable soil fungal community structure in temperate fertile Petrocalcic Argiudoll soil in a field experiment. We measured soil fungal richness, abundance and diversity along a one-year experiment (2009–2010). The plots were subjected to different tillage systems (conventional vs. zero) combined with different agricultural management histories (pasture/agriculture rotation vs. intensive agriculture). The measures were performed every three months along a year in three replicated plots. Rotation with pastures and zero tillage stimulated the saprophytic soil fungi community in detriment of pathogens. The clearest dissimilarity was given by the seasons. The results obtained from assay suggested that the seasons effect was strongest that the management or tillage on the soil fungal community.

Identifying Sustainable Grassland Management Approaches in Response to the Invasive Legume Lespedeza cuneata: A Functional Group Approach

We propose combining the filter framework model of community assembly with the passenger-driver model of non-native species behavior to help clarify the impacts of invasive species in the communities they invade and to guide sustainable management protocols. Observational field surveys and a greenhouse experiment explored the role of the invasive legume Lespedeza cuneata in the communities it invades and how natives in three functional groups—grasses, forbs, and legumes—respond to its presence. Within-site analyses from the field survey revealed differences in invaded and uninvaded areas in half of the sites, suggesting that site-specific characteristics influences whether L. cuneata’s presence corresponds to local differences in species composition. The greenhouse experiment found higher levels of saprophytic and arbuscular mycorrhizal fungi in soil conditioned by L. cuneata than in unconditioned soil. However, competition between L. cuneata or the native congener L. capitata and nine native species illustrated stronger aboveground competitive effects than belowground soil effects due to soil conditioning, with impacts differing among functional groups. The response of L. cuneata was reduced in the presence of grasses and other legumes but not forbs. Assessing the impact of L. cuneata with the combined community assembly model revealed this invasive plant acts as a driver because it alters abiotic and biotic filters to impact species composition. Managing for high grass abundance and planting native legumes will help sustain grasslands from L. cuneata invasion.

Soil Microbial Communities in Corn Fields Treated with Atoxigenic Aspergillus flavus

Aspergillus flavus refers to a diverse group of saprophytic soil fungi that includes strains producing aflatoxins (toxigenic strains) in the kernels of corn (Zea mays L.) and other crops, causing pre-harvest and post-harvest aflatoxin contamination. Some A. flavus strains are atoxigenic, and the introduction of such strains into the crop environment helps reduce toxigenic aflatoxin contamination. Corn growers in Texas have used the product FourSure™, which contains four atoxigenic strains of A. flavus; however, effects on soil microbial communities associated with these applications are unknown. We compared soil fungal and bacterial communities in corn fields treated with FourSure™ to nearby untreated (control) corn fields in Texas during the summer of 2019. Analysis of soil microbial community structure showed that total fatty acid methyl esters (FAMEs), fungal, and bacterial populations were not significantly different (p = 0.31) between the FourSure™-treated and control fields, yet corn fields located in the northern counties had more (p < 0.05) Gram—bacteria, actinobacteria, and total bacteria than fields in the southernmost county. The Gram—bacteria and actinobacteria were positively correlated (p = 0.04; r = 0.48 and 0.49, respectively) with soil water content. Similar fungal and bacterial abundances between FourSure™-treated and control fields indicated that atoxigenic A. flavus had no negative effects on soil microbial communities.

Bees Occurring in Corn Production Fields Treated with Atoxigenic Aspergillus flavus (Texas, USA)

A saprophytic soil fungus, Aspergillus flavus, produces aflatoxin (toxigenic strains) in the kernels of corn (Zea mays L.) and seeds of many other crops. Many strains of A. flavus do not produce toxigenic aflatoxin, and soil application of these atoxigenic strains is a suppressive control tactic to assist in controlling toxigenic conspecifics. Effects of atoxigenic A. flavus applications on honey bees (Apis mellifera L.) and other bees are unknown, and basic information on bee occurrences in cornfields treated with and without this biological agent is needed to inform integrated pest management in corn. Fields receiving atoxigenic A. flavus applications of FourSureTM were compared to nearby control fields in three counties in corn production regions in eastern Texas. In each cornfield, 20 bee bowl traps were deployed along four equal transects located between corn rows, with contents of the bowls (i.e., bees) retrieved after 24 h. Eleven bee genera from four families were collected from cornfields, with only two honey bees collected and zero honey bees observed in transects. The sweat bee genus Agapostemon (primarily composed of the Texas striped sweat bee A. texanus) was most abundant in cornfields (44% of the total number of bees collected), followed by long-horned bees (Melissodes spp., 24%). The southernmost county (i.e., San Patricio) produced over 80% of the total number of bees collected. Bee numbers occurring in cornfields with applications of atoxigenic A. flavus applications were not significantly different from those of nearby control fields. Although not statistically significant, total numbers of bees tended to be lower in FourSure-treated fields than in control fields. More extensive research on bee abundances in relation to the effect of atoxigenic A. flavus is warranted.

EFFECT OF INVASIVE Ageratina adenophora ON SPECIES RICHNESS AND COMPOSITION OF SAPROTROPHIC AND PATHOGENIC SOIL FUNGI

Belowground modification of soil microbial community by invasive plants is well evident. Similar instances of Ageratina adenophora invasion have been reported. This study was aimed to determine the effect of A. adenophora invasion on species richness, species or community composition and occurrence frequency of soil fungi. These parameters were analyzed using culture method on invaded and uninvaded soils. Species richness of soil fungi was lower in the A. adenophora invaded soil compared to the uninvaded soil. The occurrence frequency of particular fungi was different for those two soil conditions. A. adenophora also altered soil fungi species composition in the invaded soil by replacing saprophytic fungi and accumulating pathogenic fungi. Thus, A. adenophora is associated to lower species richness of saprophytic soil fungi and high occurrence frequency of pathogenic soil fungi. This study concluded that the invasive A. adenophora modifies belowground soil fungi communities as one of the mechanisms involved in the successful invasion of A. adenophora.

A Cellular Fusion Cascade Regulated by LaeA Is Required for Sclerotial Development in Aspergillus flavus.

Aspergillus flavus is a saprophytic soil fungus that poses a serious threat worldwide as it contaminates many food and feed crops with the carcinogenic mycotoxin called aflatoxin. This pathogen persists as sclerotia in the soil which enables fungal survival in harsh environmental conditions. Sclerotia formation by A. flavus depends on successful cell communication and hyphal fusion events. Loss of LaeA, a conserved developmental regulator in fungi, abolishes sclerotia formation in this species whereas overexpression (OE) of laeA results in enhanced sclerotia production. Here we demonstrate that sclerotia loss and inability to form heterokaryons in A. flavusΔlaeA is mediated by homologs of the Neurospora crassa ham (hyphal anastomosis) genes termed hamE-I in A. flavus. LaeA positively regulates ham gene expression and deletion of hamF, G, H, or I phenocopies ΔlaeA as demonstrated by heterokaryon and sclerotia loss and reduced aflatoxin synthesis and virulence of these mutants. Deletion of hamE showed a less severe phenotype. hamE-I homologs are positively regulated by the clock controlled transcription factor ADV-1 in N. crassa. Similarly, the ADV-1 homolog NosA regulates hamE-I expression in A. flavus, is required for sclerotial development and is itself positively regulated by LaeA. We speculate that a putative LaeA>NosA>fusion cascade underlies the previously described circadian clock regulation of sclerotia production in A. flavus.

Degradability of polylactide films by commercial microbiological preparations for household composters

Abstract Environmentally friendly polymers such as polylactide are increasingly becoming available for use in packaging applications. The main advantages of polylactide packaging are evident. Polylactide is based on renewable resources and can be degraded in compost or soil. The studies on degradability of polylactide (PLA) films by commercial preparation of mixture of multi-active saprophytic soil microorganisms, bacteria, actinomycetes and fungi have been done. Unmodified PLA film, metalized co-extruded PLA film and modified by silicon oxide PLA film were incubated in the liquid nutritious medium (TSB) prepared to support the growth of microorganisms. The degradability of polylactide films was examined by macro and microscopic observations of surface, changes of mass and crystallinity of polymer samples before and after incubation. The obtained results indicate that the degradation of polylactide was accelerated by the presence of a biological vaccine. It was found that PLA degradation in the inoculated TSB broth was a result of both: enzymatic and chemical hydrolysis.

Suppression of Aflatoxin Biosynthesis in Aspergillus flavus by 2-Phenylethanol Is Associated with Stimulated Growth and Decreased Degradation of Branched-Chain Amino Acids.

The saprophytic soil fungus Aspergillus flavus infects crops and produces aflatoxin. Pichia anomala, which is a biocontrol yeast and produces the major volatile 2-phenylethanol (2-PE), is able to reduce growth of A. flavus and aflatoxin production when applied onto pistachio trees. High levels of 2-PE are lethal to A. flavus and other fungi. However, at low levels, the underlying mechanism of 2-PE to inhibit aflatoxin production remains unclear. In this study, we characterized the temporal transcriptome response of A. flavus to 2-PE at a subinhibitory level (1 µL/mL) using RNA-Seq technology and bioinformatics tools. The treatment during the entire 72 h experimental period resulted in 131 of the total A. flavus 13,485 genes to be significantly impacted, of which 82 genes exhibited decreased expression. They included those encoding conidiation proteins and involved in cyclopiazonic acid biosynthesis. All genes in the aflatoxin gene cluster were also significantly decreased during the first 48 h treatment. Gene Ontology (GO) analyses showed that biological processes with GO terms related to catabolism of propionate and branched-chain amino acids (valine, leucine and isoleucine) were significantly enriched in the down-regulated gene group, while those associated with ribosome biogenesis, translation, and biosynthesis of α-amino acids were over-represented among the up-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that metabolic pathways negatively impacted among the down-regulated genes parallel to those active at 30 °C, a condition conducive to aflatoxin biosynthesis. In contrast, metabolic pathways positively related to the up-regulated gene group resembled those at 37 °C, which favors rapid fungal growth and is inhibitory to aflatoxin biosynthesis. The results showed that 2-PE at a low level stimulated active growth of A. flavus but concomitantly rendered decreased activities in branched-chain amino acid degradation. Since secondary metabolism occurs after active growth has ceased, this growth stimulation resulted in suppression of expression of aflatoxin biosynthesis genes. On the other hand, increased activities in degradation pathways for branched-chain amino acids probably are required for the activation of the aflatoxin pathway by providing building blocks and energy regeneration. Metabolic flux in primary metabolism apparently has an important role in the expression of genes of secondary metabolism.

Development of a Selective Medium for the Fungal Pathogen Cylindrocarpon destructans Using Radicicol.

The soil-borne ascomycete fungus Cylindrocarpon destructans causes ginseng root rot disease and produces various secondary metabolites such as brefeldin A and radicicol. The slow growth of this fungus compared with other plant pathogenic and saprophytic fungi in soil disturbs isolation of this fungus from soil and infected ginseng. In this study, we developed a selective medium for C. destructans using radicicol produced by this fungus. Supplementing 50 mg/L of radicicol to medium inhibited the mycelia growth of other fungi including Botrytis cinerea, Rhizoctonia solani and Alternaria panax, but did not affect the growth of C. destructans. In addition, conidia germination of other fungal species except for C. destructans was inhibited in submerged culture supplemented with radicicol. This medium provides a very efficient tool for isolating C. destructans and also can be used as an enrichment medium for this fungus.

Effect of saprophytic fungi on tomato pathogens: Fusarium oxysporum f. lycopersici and Verticillium albo-atrum in the soil substratum

The biotic relations were studied in garden alfalfa soil between <i>Fusarium oxysporum F. Lycopersici</i> and <i>Verticillum albo-atrum</i> and saprophytic soil fungi. The presence of the latter had an inhibitory effect on the development of pathogens and the pathologic symptoms in the tomatos. It was found that real development of plants. A change of the glasshouse soil from under alfalfa may be favourable for preventing infection of tomatoes.

Genome-wide analysis of the Zn(II)2Cys6 zinc cluster-encoding gene family in Aspergillus flavus

Proteins with a Zn(II)₂Cys₆ domain, Cys-X₂-Cys-X₆-Cys-X₅₋₁₂-Cys-X₂-Cys-X₆₋₉-Cys (hereafter, referred to as the C6 domain), form a subclass of zinc finger proteins found exclusively in fungi and yeast. Genome sequence databases of Saccharomyces cerevisiae and Candida albicans have provided an overview of this family of genes. Annotation of this gene family in most fungal genomes is still far from perfect and refined bioinformatic algorithms are urgently needed. Aspergillus flavus is a saprophytic soil fungus that can produce the carcinogenic aflatoxin. It is the second leading causative agent of invasive aspergillosis. The 37-Mb genome of A. flavus is predicted to encode 12,000 proteins. Two and a half percent of the total proteins are estimated to contain the C6 domain, more than twofold greater than those estimated for yeast, which is about 1 %. The variability in the spacing between cysteines, C₃-C₄ and C₅-C₆, in the zinc cluster enables classification of the domains into distinct subgroups, which are also well conserved in Aspergillus nidulans. Sixty-six percent (202/306) of the A. flavus C6 proteins contain a specific transcription factor domain, and 7 % contain a domain of unknown function, DUF3468. Two A. nidulans C6 proteins containing the DUF3468 are involved in asexual conidiation and another two in sexual differentiation. In the anamorphic A. flavus, a homolog of the latter lacks the C6 domain. A. flavus being heterothallic and reproducing mainly through conidiation appears to have lost some components involved in homothallic sexual development. Of the 55 predicted gene clusters thought to be involved in production of secondary metabolites, only about half have a C6-encoding gene in or near the gene clusters. The features revealed by the A. flavus C6 proteins likely are common for other ascomycete fungi.

Aspergillus flavus

Aspergillus flavus is saprophytic soil fungus that infects and contaminates preharvest and postharvest seed crops with the carcinogenic secondary metabolite aflatoxin. The fungus is also an opportunistic animal and human pathogen causing aspergillosis diseases with incidence increasing in the immunocompromised population. Whole genome sequences of A. flavus have been released and reveal 55 secondary metabolite clusters that are regulated by different environmental regimes and the global secondary metabolite regulators LaeA and VeA. Characteristics of A. flavus associated with pathogenicity and niche specialization include secondary metabolite production, enzyme elaboration, and a sophisticated oxylipin host crosstalk associated with a quorum-like development program. One of the more promising strategies in field control involves the use of atoxic strains of A. flavus in competitive exclusion studies. In this review, we discuss A. flavus as an agricultural and medical threat and summarize recent research advances in genomics, elucidation of parameters of pathogenicity, and control measures.

Pulmonary adiaspiromycosis: The first reported case in Turkey

Adiaspiromycosis is a world wide airborne infection and is a pulmonary disease in humans caused by the fungus Chrysosporium parvum var crescens (Emmonsia parva) . It is caused by inhalation of spores of the saprophytic soil fungus. The spherules induce a granulomatous reaction, in which a single spherule is surrounded by a fibronecrotic and suppurative or fibrous granuloma. The disease can be localized and asymptomatic, or disseminated, occasionally severe, or even fatal. Reticulonodular infiltrates are the most common radiographic manifestations, with localized infiltrates occurring occasionally. We present a case with bilateral diffuse interstitial micronodular infiltration and granulomatous inflammation in the lung. The larvae of adiaspiromycosis visualized in the center of granulomatous inflammation by histopathologic examination of the lung biospy specimens. We aimed to discuss the very rare cause of diffuse interstitial and granulomatous inflammation of lung.

Fungal effects on seed bank persistence and potential applications in weed biocontrol: A review

Summary Seed bank formation plays an important role in plant population dynamics. However, buried seeds face several mortality factors, including the decay caused by microbial activity. Recent seed burial studies involving both fungicide-treated seeds and untreated seeds provide evidence for the importance of saprophytic soil fungi as a seed mortality factor. In this review, we summarize the available evidence. We discuss the influence of abiotic and biotic environmental factors, the specificity of plant-fungal associations at the seed level and mechanisms of resistance to seed decay. Finally, we discuss implications for plant communities and for the biocontrol of agricultural weeds.

Optimization of culture conditions for production of the anti-tubercular alkaloid hirsutellone A by Trichoderma gelatinosum BCC 7579

This work aimed to optimize the culture conditions for production of a novel and potent anti-tubercular alkaloid, hirsutellone A, by the saprophytic soil fungus Trichoderma gelatinosum BCC 7579. The fungus was initially cultured in shake flasks at 25 degrees C in the potato dextrose broth (PDB) supplemented with various carbon and nitrogen sources and mineral salts to select suitable medium for mycelial growth and hirsutellone A production. Cultivation conditions were further optimized by adjusting initial pH and changing temperature levels to maximize the production of hirsutellone A. The optimal condition that increased the production of hirsutellone A from 19.04 mg l(-1), obtained from basal condition, to 610.55 mg l(-1) and reduced the cultivation time from 40 to 6 days was to cultivate in a shaker at 200 rev min(-1) at 25 degrees C in PDB plus 20 g l(-1) soluble starch, 10 g l(-1) peptone and 2.5% (v/v) salt solution with initial pH of 7. Production of hirsutellone A in larger-scale using a 5-l batch fermenter was also completed yielding 958 mg l(-1) of hirsutellone A within 6 days. The suitable culture conditions for hirsutellone A production by T. gelatinosum BCC 7579 was the cultivation in 5-l fermenter at 25 degrees C in PDB plus 20 g l(-1) soluble starch, 10 g l(-1) peptone and 2.5% (v/v) salt solution with an initial pH of 7. The production of hirsutellone A in a fermenter to obtain a high yield and reduce an incubation period will become very useful in anti-tubercular drug development process in the future.

A microtiter plate procedure for evaluating fungal functional diversity on nitrogen substrates

Ascertaining the effects of anthropogenic disturbance on belowground diversity is of paramount importance because pollution from agricultural practices and industrialization are increasing worldwide. Although we have methods for evaluating soil microbial function with respect to carbon use our ability to evaluate use of other compounds is limited. Because N cycling is of paramount importance in ecosystem stability, evaluation of the ability of saprophytic soil fungi to use a variety of N sources would provide important information on possible alterations in ecosystem stability with disturbance. Herein is described a procedure (soil Nitrolog) for evaluating fungal functional diversity on a suite of 95 different N substrates. The soil Nitrolog procedure was evaluated by testing fungal functional diversity at two sites in Big Bend National Park (Chihuahuan Desert), differing in elevation and plant community composition. The soil Nitrolog procedure distinguished between the two sites based on overall use of the 95 N substrates. In addition the procedure detected differences in individual substrate use based on site specific plant compounds in response to changes in the amount of N entering these ecosystems from anthropogenic inputs.

A microtiter plate procedure for evaluating fungal functional diversity on nitrogen substrates

Ascertaining the effects of anthropogenic disturbance on belowground diversity is of paramount importance because pollution from agricultural practices and industrialization are increasing worldwide. Although we have methods for evaluating soil microbial function with respect to carbon use our ability to evaluate use of other compounds is limited. Because N cycling is of paramount importance in ecosystem stability, evaluation of the ability of saprophytic soil fungi to use a variety of N sources would provide important information on possible alterations in ecosystem stability with disturbance. Herein is described a procedure (soil Nitrolog) for evaluating fungal functional diversity on a suite of 95 different N substrates. The soil Nitrolog procedure was evaluated by testing fungal functional diversity at two sites in Big Bend National Park (Chihuahuan Desert), differing in elevation and plant community composition. The soil Nitrolog procedure distinguished between the two sites based on overall use of the 95 N substrates. In addition the procedure detected differences in individual substrate use based on site specific plant compounds in response to changes in the amount of N entering these ecosystems from anthropogenic inputs.