Fungal Counterparts Research Articles

Covalent labeling of the Arabidopsis plasma membrane H+-ATPase reveals 3D conformational changes involving the C-terminal regulatory domain.

The plasma membrane proton pump is the primary energy transducing, electrogenic ion pump of the plasma membrane in plants and fungi. Compared to its fungal counterpart, the plant plasma membrane proton pump's regulatory C-terminal domain (CTD) contains an additional regulatory segment that links multiple sensory pathways regulating plant cell length through phosphorylation and recruitment of regulatory 14-3-3 proteins. However, a complete structural model of a plant proton pump is lacking. Here, we performed covalent labeling with mass spectrometric analysis (CL-MS) on the Arabidopsis pump AHA2 to identify potential interactions between the CTD and the catalytic domains. Our results suggest that autoinhibition in the plant enzyme is much more structurally complex than in the fungal enzyme.

Identification of a robust bacterial pyranose oxidase that displays an unusual pH dependence

Pyranose oxidases are valuable biocatalysts, yet only a handful of bacterial pyranose oxidases are known. These bacterial enzymes exhibit noteworthy distinctions from their extensively characterized fungal counterparts, encompassing variations in substrate specificity and structural attributes. Herein a bacterial pyranose oxidase from Oscillatoria princeps (OPOx) was biochemically characterized in detail. In contrast to the fungal pyranose oxidases, OPOx could be well expressed in Escherichia coli as soluble, fully flavinylated and active oxidase. It was found to be highly thermostable (melting temperature >90 ⁰C) and showed activity on glucose, exhibiting an exceptionally low KM value (48 μM). Elucidation of its crystal structure revealed similarities with fungal pyranose oxidases, such as being a tetramer with a large central void leading to a narrow substrate access tunnel. In the active site, the FAD cofactor is covalently bound to a histidine. OPOx displays a relatively narrow pH optimum for activity with a sharp decline at relatively basic pH values which is accompanied with a drastic change in its flavin absorbance spectrum. The pH-dependent switch in flavin absorbance features and oxidase activity was shown to be fully reversible. It is hypothesized that a glutamic acid helps to stabilize the protonated form of the histidine that is tethered to the FAD. OPOx presents itself as a valuable biocatalyst as it is highly robust, well-expressed in E. coli, shows low KM values for monosaccharides and has a peculiar pH dependent “on-off switch”.

Diversity of Rhizophydiales (Chytridiomycota) in Thailand: unveiling the hidden gems of the Kingdom

Chytrids, often overshadowed by their other fungal counterparts, take center stage as we unravel the mysteries surrounding new species within Rhizophydiales and explore their unique characteristics. In the broader spectrum of chytrids, their significance lies not only in their roles as decomposers but also as key players in nutrient cycling within aquatic ecosystems as parasites and saprobes. Baited soil and aquatic samples collected from various provinces of Thailand, yielded new species of the Rhizophydiales (Chytridiomycota), some of which expanded previously single species genera. Our investigation incorporated a combination of morphological and phylogenetic approaches, enabling us to identify these isolates as distinct taxa. The novel isolates possess distinguishing features, such as variations in size and shape of the sporangium and zoospores, that somewhat differentiate them from described taxa. To confirm the novelty of the species, we employed robust phylogenetic analyses using maximum likelihood and bayesian methods. The results provided strong support for the presence of eight distinct lineages within the Rhizophydiales, representing our newly discovered species. Furthermore, we employed Poisson Tree Processes to infer putative species boundaries and supplement evidence for the establishment of our new Rhizophydiales species. By meticulously exploring their morphological characteristics and genetic makeup, we expand the known catalogue of fungal diversity by describing Alphamyces thailandicus, Angulomyces ubonensis, Gorgonomyces aquaticus, G. chiangraiensis, G. limnicus, Pateramyces pingflumenensis, Terramyces aquatica, and T. flumenensis and also provide valuable insights into the intricacies of this order. This newfound knowledge not only enriches our understanding of Rhizophydiales but also contributes significantly to the broader field of mycology, addressing a critical gap in the documentation of fungal species. The identification and characterization of these eight novel species mark a noteworthy stride towards a more comprehensive comprehension of fungal ecosystems and their vital role.

Exploration of three Dyadobacter fermentans enzymes uncovers molecular activity determinants in CE15

Glucuronoyl esterases (GEs) are serine-type hydrolase enzymes belonging to carbohydrate esterase family 15 (CE15), and they play a central role in the reduction of recalcitrance in plant cell walls by cleaving ester linkages between glucuronoxylan and lignin in lignocellulose. Recent studies have suggested that bacterial CE15 enzymes are more heterogeneous in terms of sequence, structure, and substrate preferences than their fungal counterparts. However, the sequence space of bacterial GEs has still not been fully explored, and further studies on diverse enzymes could provide novel insights into new catalysts of biotechnological interest. To expand our knowledge on this family of enzymes, we investigated three unique CE15 members encoded by Dyadobacter fermentans NS114T, a Gram-negative bacterium found endophytically in maize/corn (Zea mays). The enzymes are dissimilar, sharing ≤ 39% sequence identity to each other‚ and were considerably different in their activities towards synthetic substrates. Combined analysis of their primary sequences and structural predictions aided in establishing hypotheses regarding specificity determinants within CE15, and these were tested using enzyme variants attempting to shift the activity profiles. Together, the results expand our existing knowledge of CE15, shed light into the molecular determinants defining specificity, and support the recent thesis that diverse GEs encoded by a single microorganism may have evolved to fulfil different physiological functions.Key points• D. fermentans encodes three CE15 enzymes with diverse sequences and specificities• The Region 2 inserts in bacterial GEs may directly influence enzyme activity• Rational amino acid substitutions improved the poor activity of the DfCE15A enzyme

Isolation and Analysis of the Palynomorphs from Khadro Formation Exposed at Ranikot Fort Area Sindh, Pakistan

Seventeen (17) palynomorphs were found from the Khadro Formation comprises of sandstone, shale, and limestone exposed at Ranikot Fort area Sindh, Pakistan. Palynomorphs are microfossils, possessing organic-walled microscopic organisms, their size range is from 5-500 µ (micrometers). Majority of the samples contained angiospermic and algal microfossils. Algal remains indicated the prevalence of sub-tropical to tropical climate, in which marine environmental species were Chaetomorpha akineta, Zygnema terrestre and Synechococcus aeruginosus and also including fresh water species such as, Pinnularia denticulata, Oscillatoria vizagapatensis and Genecularia sp. Arecaceae & Nymphaeaceae also indicated the fresh water vegetation. The fungal counterparts viz,; Dicellaesporites minutus inferred the deposition time of Khadro Formation and the environmental conditions was humid, hot, and with heavy rain fall. Presence of the Pteriodophytic spores (Laevigatosporites sp.) indicated that environment was deltaic, swampy and being estuarine. From Palynomorphs of different groups based on distribution pattern, confirms that during deposition time of Khadro Formation at early environmental condition was hot.

Enhanced transport of bacteria along root systems by protists can impact plant health.

Soil protists have been shown to contribute to the structure and function of the rhizosphere in a variety of ways. Protists are key contributors to nutrient cycling through the microbial loop, where biomass is digested by protists and otherwise stored nutrients are returned to the environment. Protists have also been shown to feed on plant pathogenic bacteria and alter root microbiomes in ways that may benefit plants. Recently, a mechanism involving bacterial transport, facilitated by protists, has been hypothesized to contribute to the spatial distribution of bacteria in the rhizosphere. Here, we observe the differential abilities of three soil protists: a ciliate (Colpoda sp.), a flagellate (Cercomonas sp.), and a naked amoeba (Acanthamoeba castellanii) to transport nitrogen-fixing Sinorhizobium meliloti to infectible root tips. Co-inoculation of protists plus S. meliloti resulted in the movement of bacteria, as measured by the presence of nitrogen-fixing nodules, up to 15 cm farther down the root systems when compared to plants inoculated with S. meliloti alone. Co-inoculation of the ciliate, Colpoda sp., with S. meliloti, resulted in shoot weights that were similar to plants that grew in nitrogen-replete potting mix. Colpoda sp.-feeding style and motility likely contributed to their success at transporting bacteria through the rhizosphere. We observed that the addition of protists alone without the co-inoculum of S. meliloti resulted in plants with larger shoot weights than control plants. Follow-up experiments showed that protists plus their associated microbiomes were aiding in plant health, likely through means of nutrient cycling.IMPORTANCEProtists represent a significant portion of the rhizosphere microbiome and have been shown to contribute to plant health, yet they are understudied compared to their bacterial and fungal counterparts. This study elucidates their role in the rhizosphere community and suggests a mechanism by which protists can be used to move bacteria along plant roots. We found that the co-inoculation of protists with nitrogen-fixing beneficial bacteria, Sinorhizobium meliloti, resulted in nodules farther down the roots when compared to plants inoculated with S. meliloti alone, and shoot weights similar to plants that received nitrogen fertilizer. These data illustrate the ability of protists to transport viable bacteria to uninhabited regions of the root system.

Biosynthesis of a bacterial meroterpenoid reveals a non-canonical class II meroterpenoid cyclase.

Meroterpenoids are hybrid natural products that arise from the integration of terpenoid and non-terpenoid biosynthetic pathways. While the biosynthesis of fungal meroterpenoids typically follows a well-established sequence of prenylation, epoxidation, and cyclization, the pathways for bacterial perhydrophenanthrene meroterpenoids remain poorly understood. In this study, we report the construction of an engineered metabolic pathway in Streptomyces for the production of the bacterial meroterpenoid, atolypene A (1). Our research reveals a novel biosynthetic pathway wherein the structure of 1 is assembled through a distinct sequence of epoxidation, prenylation, and cyclization, divergent from its fungal counterparts. We demonstrate that the noncanonical class II meroterpenoid cyclase (MTC) AtoE initiates cyclization by protonating the epoxide via the E314 residue, which acts as a Brønsted acid within the characteristic xxxE314TAE motif. Additionally, bioinformatic analysis of biosynthetic gene clusters (BGCs) that contain AtoE-like MTCs supports that bacteria have the potential to produce a wide array of meroterpenoids.

Crystal Structure of Fungal Nonspecific Phospholipase C Unveils a Distinct Catalytic Mechanism.

Nonspecific phospholipase C (NPC) plays a pivotal role in hydrolyzing phospholipids, releasing diacylglycerol─an essential second messenger. Extensive research has elucidated the structure and function of bacterial and plant NPCs, but our understanding of their fungal counterparts remains limited. Here, we present the first crystal structure of a fungal NPC derived from Rasamsonia emersonii (RePLC), unraveling its distinguishable features divergent from other known phospholipase C. Remarkably, the structure of RePLC contains solely the phosphoesterase domain without the crucial C-terminal domain (CTD) found in plant NPCs, although CTD is important for their activity. Through a comparative analysis of structural features among NPCs from diverse species combined with structure-based mutation analyses and bioinformatics methods, we propose a potential molecular mechanism that may universally underlie the catalysis of phospholipid hydrolysis in fungal NPCs. Furthermore, our study sheds light on the captivating evolutionary trajectory of enzymes across diverse species.

A high throughput screening process and quick isolation of novel lignin-degrading microbes from large number of natural biomasses

High throughput screening approaches can significantly speed up the identification of novel enzymes from natural microbial consortiums. A two-step high throughput screening process was proposed and explored to screen lignin-degrading microorganisms. By employing this modified culture enrichment method and screening based on enzyme activity, a total of 82 bacterial and 46 fungal strains were isolated from fifty decayed wood samples (100 liquid cultures) collected from the banks of the Ottawa River in Canada. Among them, ten bacterial and five fungal strains were selected and identified based on their high laccase activities by 16S rDNA and ITS gene sequencing, respectively. The study identified bacterial strains from various genera including Serratia, Enterobacter, Raoultella, and Bacillus, along with fungal counterparts including Mucor, Trametes, Conifera and Aspergillus. Moreover, Aspergillus sydowii (AORF21), Mucor sp. (AORF43), Trametes versicolor (AORF3) and Enterobacter sp. (AORB55) exhibited xylanase and β- glucanase activities in addition to laccase production. The proposed approach allowed for the quick identification of promising consortia and enhanced the chance of isolating desired strains based on desired enzyme activities. This method is not limited to lignocellulose and lignin-degrading microorganisms but can be applied to identify novel microbial strains and enzymes from different natural samples.

Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses.

Mycoviruses (viruses of fungi) are ubiquitous throughout the fungal kingdom and are currently classified into 23 viral families and the genus botybirnavirus by the International Committee on the Taxonomy of Viruses (ICTV). The primary focus of mycoviral research has been on mycoviruses that infect plant pathogenic fungi, due to the ability of some to reduce the virulence of their host and thus act as potential biocontrol against these fungi. However, mycoviruses lack extracellular transmission mechanisms and rely on intercellular transmission through the hyphal anastomosis, which impedes successful transmission between different fungal strains. This review provides a comprehensive overview of mycoviruses, including their origins, host range, taxonomic classification into families, effects on their fungal counterparts, and the techniques employed in their discovery. The application of mycoviruses as biocontrol agents of plant pathogenic fungi is also discussed.

Role of Fungi in Imparting General Disease Suppressiveness in Soil from Organic Field.

Soil microbial communities are key players responsible for imparting suppressive potential to the soil against soil-borne phytopathogens. Fungi have an immense potential to inhibit soil-borne phytopathogens, but the fungal counterpart has been less explored in this context. We assessed the composition of fungal communities in soil under long-term organic and conventional farmingpractice, and control soil. The disease-suppressive potential of organic field was already established. A comparative analysis of the disease suppressiveness contributed by the fungal component of soil from conventional and organic farms was assessed using dual culture assays. The quantification of biocontrol markers and total fungi was done; the characterization of fungal community was carried out using ITS-based amplicon sequencing. Soil from organic field exhibited higher disease-suppressive potential thanthat from conventional farming, against the pathogens selected for the study. Higher levels of hydrolytic enzymes such as chitinase and cellulase, and siderophore production were observed in soil from the organic field compared to the conventional field. Differences in community composition were observed under conventional and organic farming, with soil from organic field exhibiting specific enrichment of key biocontrol fungal genera. The fungal alpha diversity was lower in soil from the organic field compared to the conventional field. Our results highlight the role of fungi in contributing to general disease-suppressive ability of the soil against phytopathogens. The identification of fungal taxa specifically associated with organic farming can aid in understanding the mechanism of disease suppression under such a practice, and can be exploited to induce general disease suppressiveness in otherwise conducive soil.

LCN2-Fungal siderophore-iron binding and uptake leads to oxidative stress and cell death in hepatocellular carcinoma cell line HepG2

Microorganisms produce non-ribosomal peptides called siderophores for the purpose of iron acquisition. Mammalian immune system is well-known for producing small secretory proteins called lipocalins upon bacterial infection. These proteins sequester siderophores produced by invading bacterial pathogens rendering them unable to acquire iron from the host. However, this is not their sole function. In addition to transferrin and lactoferrin, lipocalins are also known to transport siderophore-bound iron to the host cells. While binding of bacterial siderophores with human lipocalin is well studied, binding of the fungal counterpart is still not confirmed and fully understood. Apart from pathogen-affected cells, developing cancerous cells also show varying expression level of different proteins including those involved in iron transport. The possibility of exogenous fungal siderophore-mediated iron transport via lipocalin and its receptor in mammalian cells has not yet been explored much. In present investigation we have checked differential expression of human lipocalin, LCN2 in hepatocellular carcinoma cell lines HepG2 as well as its normal counterpart WRL-68 and computationally determined the feasibility of LCN2 binding with fungal siderophore. Further in case of a stable complex being formed, whether this complex has the ability to transport iron through its specific receptor was assessed. Also, we have tried to explore possible mechanism of fungal-siderophore mediated oxidative stress leading to significant cell death in cancerous cells. This study will thus be useful towards finding a new way of treating hepatocellular carcinoma via inducing siderophore-mediated cell death in cancerous cells. Communicated by Ramaswamy H. Sarma

Spindle Assembly and Mitosis in Plants.

In contrast to well-studied fungal and animal cells, plant cells assemble bipolar spindles that exhibit a great deal of plasticity in the absence of structurally defined microtubule-organizing centers like the centrosome. While plants employ some evolutionarily conserved proteins to regulate spindle morphogenesis and remodeling, many essential spindle assembly factors found in vertebrates are either missing or not required for producing the plant bipolar microtubule array. Plants also produce proteins distantly related to their fungal and animal counterparts to regulate critical events such as the spindle assembly checkpoint. Plant spindle assembly initiates with microtubule nucleation on the nuclear envelope followed by bipolarization into the prophase spindle. After nuclear envelope breakdown, kinetochore fibers are assembled and unified into the spindle apparatus with convergent poles. Of note, compared to fungal and animal systems, relatively little is known about how plant cells remodel the spindle microtubule array during anaphase. Uncovering mitotic functions of novel proteins for spindle assembly in plants will illuminate both common and divergent mechanisms employed by different eukaryotic organisms to segregate genetic materials.

Seagrass ‘fairy circles’ on the Isles of Scilly

AbstractPerfectly circular patches bare of vegetation in otherwise continuous swards of seagrass, and perfect circles of seagrass with lush fringes of shoots on the outer margins but with virtually bare centres, have both attracted popular attention as ‘fairy circles’ or ‘fairy rings’ in view of the folklore surrounding the supernatural origins of their terrestrial fungal counterparts. Aerial photographic and satellite surveys show that, on the Isles of Scilly, circles of Zostera marina of the second type occur sporadically, with exceptionally prolific clusters in specific localities associated with the colonization of bare substratum after disturbance, gradually disappearing over the period of this study at one site and appearing at another. Their abundance is the highest recorded anywhere in the world. Early suggestions that they represent seaweed growth on the stones of ancient hut-circles, submerged for centuries as a result of sea-level rise, are refuted. It is argued that they result from the unrestricted clonal growth of genets arising from individual Zostera seedlings, expanding equally in two dimensions and colonizing vacant habitat, with the older central shoots senescing and dying. Diameters of the circles constitute a stepwise increase in size, and the growth increments may represent a similar rate of seasonal growth in consecutive years, implying a linear rhizome growth rate of ~2.5 m year−1, which would be exceptional for Zostera marina, but which is supported by an observation on circles exposed on a low spring tide and would be an evolutionary adaptation for rapid recolonization in such a physically disturbed environment.

Engineering Microbial Biofilms for Improved Productivity of Biochemicals Important in Restoration of Degraded Ecosystems

Biofilms are being engineered in-vitro to produce numerous commodities like biofertilizers, pharmaceuticals, biofuels and electricity, the efficacies of which rely on the biochemicals secreted by the biofilms i.e. extracellular polymeric substances (EPS). It has been shown that once EPS-biochemicals of developed biofilms are applied to an ecosystem, they can restore degraded complex ecosystem networks for improved ecosystem functioning and sustainability. Identification of the EPS biochemicals and understanding their contributions to the network interactions in particular, are at initial stage. In the present study, using Aspergillus niger, Nostoc sp., and gram (-) Stenotrophomonas maltophilia & gram (+) Bacillus subtilis as test fungal (F), cyanobacterial (C), and bacterial (B) counterparts, respectively we analyzed morphology and biochemical parameters of fungal-bacterial (FBBs), fungal-cyanobacterial (FCBs), cyanobacterial-bacterial (CBBs), and fungal-cyanobacterial-bacterial biofilms (FCBBs). Results revealed that the FCBBs produced the highest concentrations of lipids, proteins, and polysaccharides whereas FBBs generated the highest diversity of biochemicals. Bacterial type (i.e. gram + or -) and microbial composition in the biofilm affected the biochemical production. Ecologically and industrially important diverse biochemicals which are used individually as medicines, bioremediating agents and industrial chemicals in human society with certain adverse and beneficial effects were detected in the biofilm-EPS. However, in the nature, simultaneous action of those diverse biochemicals applied as biofertilizers has already shown a huge potential to restore the entire agroecosystems degraded due to farmers’ detrimental practices. This striking difference in utilization of the biochemicals and their enhanced effect when they act simultaneously needs further investigations for their better applications.

Identification of Chitin synthase and Chitinase genes in three ontogenetic stages from Thecaphora frezii, the causal agent of peanut smut disease

Chitin is one of the major components of the fungal cell wall. Chitin synthases participate in its biosynthesis and chitinases in its degradation. Thecaphora frezii (T. frezii) is a phytopathogenic fungus that affects peanut crops. We identified the presence of eight Chitin Synthases and four Chitinases in T. frezii, which present identities greater than 60%, when compared with their fungal counterpart Ustilago maydis. “Signature sequences” QXXEY, EDRXL and QXRRW were identified in all Chitin synthases and the DxxDxDxE sequence was seen in three Chitinases. A variable level in the mRNA expression of different enzymes was found in the three ontogenetic stages (teliospore, basidiospore, and hyphae). The in vitro chitinase activity of the three structures was evaluated, observing activity only in the protein extract of hyphae and basidiospores. These findings contribute to better understanding of the pathogen (T. frezii) biology.

A new and unusual β-glucosidase from Aspergillus fumigatus: Catalytic activity at high temperatures and glucose tolerance

The demand for novel enzymes with the potential to catalyze reactions at high temperatures has encouraged the exploration of new thermophilic strains in recent years. Several fungal thermophilic β-glucosidases have been described previously. However, only a few β-glucosidases meet industrial requirements, such as hydrolytic activity at high temperatures and tolerance to glucose inhibition. Because tropical areas support high species diversity, the Atlantic Forest biome can offer great opportunities for bioprospecting new β-glucosidase producers to fulfill industrial needs. This study reports the production and biochemical characterization of an unusual thermophilic β-glucosidase produced by an Aspergillus fumigatus strain isolated from the Atlantic Forest biome. This enzyme can be produced using a low-cost cultivation medium with canola meal as the substrate. The highest β-glucosidase production (24.53 U/mL) was obtained when the fungus was cultivated in 2.9% canola meal over a period of 101 h at pH 4.2, and a temperature of 40 °C. This enzyme has an optimum temperature of 80 °C, which is higher than that of almost all its known fungal counterparts. Moreover, it is highly glucose tolerant, unlike other β-glucosidases that are inhibited by this sugar, with an inhibitory constant (Ki) of 543 mM. The combination of these attributes and their sustained activity at 80 °C distinguishes this enzyme from other A. fumigatus enzymes and almost every other β-glucosidase characterized from thermotolerant fungal species described to date. Therefore, this novel enzyme is a promising target for bioethanol production. • A new A. fumigatus thermophilic and cellulolytic strain was isolated. • Canola meal was used as the carbon source to produce β-glucosidases. • Overall the process was effective in terms of β-glucosidase yield. • An unusual fungal β-glucosidase with maximum activity at 80 °C is described. • The enzyme is highly glucose tolerant with an inhibitory constant (Ki) of 543 mM.

A Chimeric Variant of Two Gentisate 1,2‐Dioxygenases with Improved Catalytic Activity, Altered Structural Conformation and Substrate Specificity

Gentisate 1,2-dioxygenases catalyze the critical ring-opening step in the metabolism of gentisate (2,5-dihydroxybenzoate) by microorganisms under aerobic conditions. Gentisate 1,2-dioxgenases from bacterial species that have been characterized to date are strictly Fe(II)-dependent and they are mostly homotetrameric in solution. In bacteria, genes coding for gentisate 1,2-dioxygenase and other enzymes in the rest of the pathway for gentisate degradation are often organized in operons. While genes and enzymes in the gentisate pathway have been relatively well-studied in bacteria, reports about their fungal counterparts remain scarce in the literature. Here, we report the biochemical characterization of two gentisate 1,2-dioxygenases from Aspergillus niger with different specific activities that appear to be encoded within two split gene clusters in the A. niger genome. These differences in activities seem to be accompanied by differences in secondary structure and oligomerization states between these two proteins in solution. Furthermore, we report the engineering of a chimeric variant consisting of two domains derived from these two A. niger gentisate 1,2-dioxgenases that shows improved activity with gentisate, altered structural conformation and substrate specificity able to cleave a substrate that neither of the two wild type gentisate 1,2-dioxygenases is able to attack.

Bacterial Communities Are More Sensitive to Water Addition Than Fungal Communities Due to Higher Soil K and Na in a Degraded Karst Ecosystem of Southwestern China.

Precipitation is predicted to become more intense in Southern China in the context of climate change; however, the responses of microbial communities to variations in soil moisture have not been well documented for karst areas. The climate is typically in a subtropical monsoon category with two different seasons: a dry season (December–May) and a wet season (June–November). Based on a randomized complete block design (RCBD), a water addition experiment (0, +20, +40, and +60% relative to local precipitation) was established in April 2017, with five replicates, in a degraded grass-shrub community. Sampling was performed in May and at the end of August of 2017. Macroelements (C, H, N, P, K, Ca, Mg, and S), microelements (Mn, Fe, Zn, and Cu), and non-essential elements (Na, Al, and Si) were quantified in the soil. The total DNA of the soil samples was analyzed through 16S rRNA amplicon by Illumina Miseq. Subsequent to the addition of water during both the dry and wet seasons, the concentrations of non-metal elements (C, H, N, S, and P, except for Si) in the soil remained relatively stable; however, metal elements (K, Na, Fe, and Mg, along with Si) increased significantly, whereas Zn and Ca decreased. During the dry season, fungal and bacterial communities were significantly distinct from those during the wet season along the PC axis 1 (p < 0.001). Water addition did not alter the compositions of bacterial or fungal communities during the dry season. However, during the wet season, water addition altered the compositions of bacterial rather than fungal community based on principal component analysis. At the phylum level, the relative abundance of Actinobacteria increased with water addition and had a significantly positive correlation with K+ (r2 = 0.70, p < 0.001) and Na+ (r2 = 0.36, p < 0.01) contents, whereas that of Acidobacteria, Planctomycetes, and Verrucomicrobia decreased and showed negative correlation with soil K and Na content, and no changes were observed for the fungal phyla. This suggests that the karst bacterial communities can be influenced by the addition of water during the wet season likely linked to changes in soil K and Na contents. These findings implied that increased rainfall might alter the elemental compositions of karst soils, and bacterial communities are likely to be more sensitive to variations in soil moisture in contrast to their fungal counterparts.

Horizontal Gene Transfer and Tandem Duplication Shape the Unique CAZyme Complement of the Mycoparasitic Oomycetes Pythium oligandrum and Pythium periplocum.

Crop protection strategies that are effective but that reduce our reliance on chemical pesticides are urgently needed to meet the UN sustainable development goals for global food security. Mycoparasitic oomycetes such as Pythium oligandrum and Pythium periplocum, have potential for the biological control of plant diseases that threaten crops and have attracted much attention due to their abilities to antagonize plant pathogens and modulate plant immunity. Studies of the molecular and genetic determinants of mycoparasitism in these species have been less well developed than those of their fungal counterparts. Carbohydrate-active enzymes (CAZymes) from P. oligandrum and P. periplocum are predicted to be important components of mycoparasitism, being involved in the degradation of the cell wall of their oomycete and fungal prey species. To explore the evolution of CAZymes of these species we performed an in silico identification and comparison of the full CAZyme complement (CAZyome) of the two mycoparasitic Pythium species (P. oligandrum and P. periplocum), with seven other Pythium species, and four Phytophthora species. Twenty CAZy gene families involved in the degradation of cellulose, hemicellulose, glucan, and chitin were expanded in, or unique to, mycoparasitic Pythium species and several of these genes were expressed during mycoparasitic interactions with either oomycete or fungal prey, as revealed by RNA sequencing and quantitative qRT-PCR. Genes from three of the cellulose and chitin degrading CAZy families (namely AA9, GH5_14, and GH19) were expanded via tandem duplication and predominantly located in gene sparse regions of the genome, suggesting these enzymes are putative pathogenicity factors able to undergo rapid evolution. In addition, five of the CAZy gene families were likely to have been obtained from other microbes by horizontal gene transfer events. The mycoparasitic species are able to utilize complex carbohydrates present in fungal cell walls, namely chitin and N-acetylglucosamine for growth, in contrast to their phytopathogenic counterparts. Nonetheless, a preference for the utilization of simple sugars for growth appears to be a common trait within the oomycete lineage.