Phylogenomics reveals extensive misidentification of fungal strains from the genus Aspergillus

Modern taxonomic classification is often based on phylogenetic analyses of a few molecular markers, although single-gene studies are still common. Here, we leverage genome-scale molecular phylogenetics (phylogenomics) of species and populations to reconstruct evolutionary relationships in a dense data set of 710 fungal genomes from the biomedically and technologically important genus Aspergillus. To do so, we generated a novel set of 1,362 high-quality molecular markers specific for Aspergillus and provided profile Hidden Markov Models for each, facilitating their use by others. Examining the resulting phylogeny helped resolve ongoing taxonomic controversies, identified new ones, and revealed extensive strain misidentification (7.59% of strains were previously misidentified), underscoring the importance of population-level sampling in species classification. These findings were corroborated using the current standard, taxonomically informative loci. These findings suggest that phylogenomics of species and populations can facilitate accurate taxonomic classifications and reconstructions of the Tree of Life.IMPORTANCEIdentification of fungal species relies on the use of molecular markers. Advances in genomic technologies have made it possible to sequence the genome of any fungal strain, making it possible to use genomic data for the accurate assignment of strains to fungal species (and for the discovery of new ones). We examined the usefulness and current limitations of genomic data using a large data set of 710 publicly available genomes from multiple strains and species of the biomedically, agriculturally, and industrially important genus Aspergillus. Our evolutionary genomic analyses revealed that nearly 8% of publicly available Aspergillus genomes are misidentified. Our work highlights the usefulness of genomic data for fungal systematic biology and suggests that systematic genome sequencing of multiple strains, including reference strains (e.g., type strains), of fungal species will be required to reduce misidentification errors in public databases.

Transcriptomic analysis using RNA sequencing and phenotypic analysis of Salmonella enterica after acid exposure for different time durations using adaptive laboratory evolution

Introduction

This study is the final part of a two-part series that delves into the molecular mechanisms driving adaptive laboratory evolution (ALE) of Salmonella enterica in acid stress. The phenotypic and transcriptomic alterations in the acid-evolved lineages (EL) of Salmonella enterica serovar Enteritidis after 70 days of acid stress exposure were analyzed.

Materials and methods

The stability of phenotypic changes observed after 70 days in acetic acid was explored after stress removal using a newly developed evolutionary lineage EL5. Additionally, the impact of short-term acid stress on the previously adapted lineage EL4 was also examined.

Results

The results indicate that the elevated antibiotic minimum inhibitory concentration (MIC) observed after exposure to acetic acid for 70 days was lost when acid stress was removed. This phenomenon was observed against human antibiotics such as meropenem, ciprofloxacin, gentamicin, and streptomycin. The MIC of meropenem in EL4 on day 70 was 0.094 mM, which dropped to 0.032 mM when removed from acetic acid stress after day 70. However, after stress reintroduction, the MIC swiftly elevated, and within 4 days, it returned to 0.094 mM. After 20 more days of adaptation in acetic acid, the meropenem MIC increased to 0.125 mM. The other human antibiotics that were tested exhibited a similar trend. The MIC of acetic acid in EL4 on day 70 was observed to be 35 mM, which remained constant even after the removal of acetic acid stress. Readaptation of EL4 in acetic acid for 20 more days caused the acetic acid MIC to increase to 37 mM. Bacterial whole genome sequencing of EL5 revealed base substitutions in several genes involved in pathogenesis, such as the phoQ and wzc genes. Transcriptomic analysis of EL5 revealed upregulation of virulence, drug resistance, toxin-antitoxin, and iron metabolism genes. Unstable Salmonella small colony variants (SSCV) of S. Enteritidis were also observed in EL5 as compared to the wild-type unevolved S. Enteritidis.

Discussion

This study presents a comprehensive understanding of the evolution of the phenotypic, genomic, and transcriptomic changes in S. Enteritidis due to prolonged acid exposure through ALE.

Adaptive laboratory evolution of Salmonella enterica in acid stress

Introduction

Adaptive laboratory evolution (ALE) studies play a crucial role in understanding the adaptation and evolution of different bacterial species. In this study, we have investigated the adaptation and evolution of Salmonella enterica serovar Enteritidis to acetic acid using ALE.

Materials and methods

Acetic acid concentrations below the minimum inhibitory concentration (sub-MIC) were used. Four evolutionary lineages (EL), namely, EL1, EL2, EL3, and EL4, of S. Enteritidis were developed, each demonstrating varying levels of resistance to acetic acid.

Results

The acetic acid MIC of EL1 remained constant at 27 mM throughout 70 days, while the MIC of EL2, EL3, and EL4 increased throughout the 70 days. EL4 was adapted to the highest concentration of acetic acid (30 mM) and demonstrated the highest increase in its MIC against acetic acid throughout the study, reaching an MIC of 35 mM on day 70. The growth rates of the evolved lineages increased over time and were dependent on the concentration of acetic acid used during the evolutionary process. EL4 had the greatest increase in growth rate, reaching 0.33 (h-1) after 70 days in the presence of 30 mM acetic acid as compared to EL1, which had a growth rate of 0.2 (h-1) after 70 days with no exposure to acetic acid. Long-term exposure to acetic acid led to an increased MIC of human antibiotics such as ciprofloxacin and meropenem against the S. enterica evolutionary lineages. The MIC of ciprofloxacin for EL1 stayed constant at 0.016 throughout the 70 days while that of EL4 increased to 0.047. Bacterial whole genome sequencing revealed single-nucleotide polymorphisms in the ELs in various genes known to be involved in S. enterica virulence, pathogenesis, and stress response including phoP, phoQ, and fhuA. We also observed genome deletions in some of the ELs as compared to the wild-type S. Enteritidis which may have contributed to the bacterial acid adaptation.

Discussion

This study highlights the potential for bacterial adaptation and evolution under environmental stress and underscores the importance of understanding the development of cross resistance to antibiotics in S. enterica populations. This study serves to enhance our understanding of the pathogenicity and survival strategies of S. enterica under acetic acid stress.

A global phylogenomic analysis of the shiitake genus Lentinula

Lentinula is a broadly distributed group of fungi that contains the cultivated shiitake mushroom, L. edodes. We sequenced 24 genomes representing eight described species and several unnamed lineages of Lentinula from 15 countries on four continents. Lentinula comprises four major clades that arose in the Oligocene, three in the Americas and one in Asia-Australasia. To expand sampling of shiitake mushrooms, we assembled 60 genomes of L. edodes from China that were previously published as raw Illumina reads and added them to our dataset. Lentinula edodes sensu lato (s. lat.) contains three lineages that may warrant recognition as species, one including a single isolate from Nepal that is the sister group to the rest of L. edodes s. lat., a second with 20 cultivars and 12 wild isolates from China, Japan, Korea, and the Russian Far East, and a third with 28 wild isolates from China, Thailand, and Vietnam. Two additional lineages in China have arisen by hybridization among the second and third groups. Genes encoding cysteine sulfoxide lyase (lecsl) and γ-glutamyl transpeptidase (leggt), which are implicated in biosynthesis of the organosulfur flavor compound lenthionine, have diversified in Lentinula. Paralogs of both genes that are unique to Lentinula (lecsl 3 and leggt 5b) are coordinately up-regulated in fruiting bodies of L. edodes. The pangenome of L. edodes s. lat. contains 20,308 groups of orthologous genes, but only 6,438 orthogroups (32%) are shared among all strains, whereas 3,444 orthogroups (17%) are found only in wild populations, which should be targeted for conservation.

Genomic and Molecular Identification of Genes Contributing to the Caspofungin Paradoxical Effect in Aspergillus fumigatus

Aspergillus fumigatus is a deadly opportunistic fungal pathogen responsible for ~100,000 annual deaths. Azoles are the first line antifungal agent used against A. fumigatus, but azole resistance has rapidly evolved making treatment challenging. Caspofungin is an important second-line therapy against invasive pulmonary aspergillosis, a severe A. fumigatus infection. Caspofungin functions by inhibiting β-1,3-glucan synthesis, a primary and essential component of the fungal cell wall. A phenomenon termed the caspofungin paradoxical effect (CPE) has been observed in several fungal species where at higher concentrations of caspofungin, chitin replaces β-1,3-glucan, morphology returns to normal, and growth rate increases. CPE appears to occur in vivo, and it is therefore clinically important to better understand the genetic contributors to CPE. We applied genomewide association (GWA) analysis and molecular genetics to identify and validate candidate genes involved in CPE. We quantified CPE across 67 clinical isolates and conducted three independent GWA analyses to identify genetic variants associated with CPE. We identified 48 single nucleotide polymorphisms (SNPs) associated with CPE. We used a CRISPR/Cas9 approach to generate gene deletion mutants for seven genes harboring candidate SNPs. Two null mutants, ΔAfu3g13230 and ΔAfu4g07080 (dscP), resulted in reduced basal growth rate and a loss of CPE. We further characterized the dscP phosphatase-null mutant and observed a significant reduction in conidia production and extremely high sensitivity to caspofungin at both low and high concentrations. Collectively, our work reveals the contribution of Afu3g13230 and dscP in CPE and sheds new light on the complex genetic interactions governing this phenotype. IMPORTANCE This is one of the first studies to apply genomewide association (GWA) analysis to identify genes involved in an Aspergillus fumigatus phenotype. A. fumigatus is an opportunistic fungal pathogen that causes hundreds of thousands of infections and ~100,000 deaths each year, and antifungal resistance has rapidly evolved in this species. A phenomenon called the caspofungin paradoxical effect (CPE) occurs in some isolates, where high concentrations of the drug lead to increased growth rate. There is clinical relevance in understanding the genetic basis of this phenotype, since caspofungin concentrations could lead to unintended adverse clinical outcomes in certain cases. Using GWA analysis, we identified several interesting candidate polymorphisms and genes and then generated gene deletion mutants to determine whether these genes were important for CPE. Two of these mutant strains (ΔAfu3g13230 and ΔAfu4g07080/ΔdscP) displayed a loss of the CPE. This study sheds light on the genes involved in clinically important phenotype CPE.

Comparative Genomics Reveals a Single Nucleotide Deletion in pksP That Results in White-Spore Phenotype in Natural Variants of Aspergillus fumigatus

Aspergillus fumigatus is a potentially deadly opportunistic human pathogen. A. fumigatus has evolved a variety of mechanisms to evade detection by the immune system. For example, the conidium surface is covered in a layer of 1,8-dihydroxynaphthalene (DHN) melanin which masks the antigen macrophages use for recognition. DHN melanin also protects conidia from ultraviolet radiation and gives A. fumigatus conidia their characteristic green-grayish color. Here, we conducted genomic analysis of two closely related white-spore natural variants of A. fumigatus in comparison to two closely related green-spore isolates to identify a genetic basis of the white-spore phenotype. Illumina whole-genome resequencing data of the four isolates was used to identify variants that were shared in the white-spore isolates and different from both the green-spore isolates and the Af293 reference genome (which is also a green-spore isolate). We identified 4,279 single nucleotide variants and 1,785 insertion/deletions fitting this pattern. Among these, we identified 64 variants predicted to be high impact, loss-of-function mutations. One of these variants is a single nucleotide deletion that results in a frameshift in pksP (Afu2g17600), the core biosynthetic gene in the DHN melanin encoding gene cluster. The frameshift mutation in the white-spore isolates leads to a truncated protein in which a phosphopantetheine attachment site (PP-binding domain) is interrupted and an additional PP-binding domain and a thioesterase domain are omitted. Growth rate analysis of white-spore and green-spore isolates at 37°C and 48°C revealed that white-spore isolates are thermosensitive. Growth rate of A. fumigatus Af293 and a pksP null mutant in the Af293 background suggests pksP is not directly involved in the thermosensitivity phenotype. Further, our study identified a mutation in a gene (Afu4g04740) associated with thermal sensitivity in yeasts which could also be responsible for the thermosensitivity of the white-spore mutants. Overall, we used comparative genomics to identify the mutation and protein alterations responsible for the white-spore phenotype of environmental isolates of A. fumigatus.

Characterization of 260 Isolates of Aspergillus Section Flavi Obtained from Sesame Seeds in Punjab, Pakistan

Sesame Sesamum indicum L. is a major oil-based seed crop that has been widely cultivated and consumed in Pakistan. Unfortunately, sesame is highly prone to Aspergillus fungal growth in the field, and under inappropriate storage conditions can become contaminated with aflatoxins, the most potent carcinogen found in nature. Here, we have isolated a high number of Aspergillus isolates from sesame seeds in fresh and stored conditions obtained from rainfed and irrigated zones of Punjab, Pakistan, and characterized them for aflatoxigenic potentials. Using morphological identification techniques, 260 isolates were grouped as potential Aspergillus section Flavi, with 126 and 134 originating from the rainfed and irrigated zones, respectively. Out of 260 in total, 188 isolates were confirmed to produce aflatoxins. There were no significant differences in potential aflatoxigenic isolates with respect to the rainfed and irrigated zones. However, the number of potential aflatoxigenic isolates was significantly higher (p < 0.05) in stored samples than that of those from fresh sesame seeds in the rainfed and irrigated zone. Whole genome sequencing and comparative analyses of 12 select isolates have revealed that one of the A. flavus isolates, which produced very low aflatoxins (AFP10), has an elevated missense variant rate, numerous high impact mutations, and a 600 base pair deletion in the norB gene. In summary, our study provides insights into aflatoxigenic potential and the associated genetic diversity of indigenous Aspergillus section Flavi isolates and potential management strategies for reducing aflatoxin contamination levels in a major crop consumed in Punjab, Pakistan.

Microbial enzymes induce colitis by reactivating triclosan in the mouse gastrointestinal tract

Emerging research supports that triclosan (TCS), an antimicrobial agent found in thousands of consumer products, exacerbates colitis and colitis-associated colorectal tumorigenesis in animal models. While the intestinal toxicities of TCS require the presence of gut microbiota, the molecular mechanisms involved have not been defined. Here we show that intestinal commensal microbes mediate metabolic activation of TCS in the colon and drive its gut toxicology. Using a range of in vitro, ex vivo, and in vivo approaches, we identify specific microbial β-glucuronidase (GUS) enzymes involved and pinpoint molecular motifs required to metabolically activate TCS in the gut. Finally, we show that targeted inhibition of bacterial GUS enzymes abolishes the colitis-promoting effects of TCS, supporting an essential role of specific microbial proteins in TCS toxicity. Together, our results define a mechanism by which intestinal microbes contribute to the metabolic activation and gut toxicity of TCS, and highlight the importance of considering the contributions of the gut microbiota in evaluating the toxic potential of environmental chemicals.

Divergence of a genomic island leads to the evolution of melanization in a halophyte root fungus

Understanding how organisms adapt to extreme living conditions is central to evolutionary biology. Dark septate endophytes (DSEs) constitute an important component of the root mycobiome and they are often able to alleviate host abiotic stresses. Here, we investigated the molecular mechanisms underlying the beneficial association between the DSE Laburnicola rhizohalophila and its host, the native halophyte Suaeda salsa, using population genomics. Based on genome-wide Fst (pairwise fixation index) and Vst analyses, which compared the variance in allele frequencies of single-nucleotide polymorphisms (SNPs) and copy number variants (CNVs), respectively, we found a high level of genetic differentiation between two populations. CNV patterns revealed population-specific expansions and contractions. Interestingly, we identified a ~20 kbp genomic island of high divergence with a strong sign of positive selection. This region contains a melanin-biosynthetic polyketide synthase gene cluster linked to six additional genes likely involved in biosynthesis, membrane trafficking, regulation, and localization of melanin. Differences in growth yield and melanin biosynthesis between the two populations grown under 2% NaCl stress suggested that this genomic island contributes to the observed differences in melanin accumulation. Our findings provide a better understanding of the genetic and evolutionary mechanisms underlying the adaptation to saline conditions of the L. rhizohalophila-S. salsa symbiosis.

Comparison of Two Aspergillus oryzae Genomes From Different Clades Reveals Independent Evolution of Alpha-Amylase Duplication, Variation in Secondary Metabolism Genes, and Differences in Primary Metabolism

Microbes (bacteria, yeasts, molds), in addition to plants and animals, were domesticated for their roles in food preservation, nutrition and flavor. Aspergillus oryzae is a domesticated filamentous fungal species traditionally used during fermentation of Asian foods and beverage, such as sake, soy sauce, and miso. To date, little is known about the extent of genome and phenotypic variation of A. oryzae isolates from different clades. Here, we used long-read Oxford Nanopore and short-read Illumina sequencing to produce a highly accurate and contiguous genome assemble of A. oryzae 14160, an industrial strain from China. To understand the relationship of this isolate, we performed phylogenetic analysis with 90 A. oryzae isolates and 1 isolate of the A. oryzae progenitor, Aspergillus flavus. This analysis showed that A. oryzae 14160 is a member of clade A, in comparison to the RIB 40 type strain, which is a member of clade F. To explore genome variation between isolates from distinct A. oryzae clades, we compared the A. oryzae 14160 genome with the complete RIB 40 genome. Our results provide evidence of independent evolution of the alpha-amylase gene duplication, which is one of the major adaptive mutations resulting from domestication. Synteny analysis revealed that both genomes have three copies of the alpha-amylase gene, but only one copy on chromosome 2 was conserved. While the RIB 40 genome had additional copies of the alpha-amylase gene on chromosomes III, and V, 14160 had a second copy on chromosome II and an third copy on chromosome VI. Additionally, we identified hundreds of lineage specific genes, and putative high impact mutations in genes involved in secondary metabolism, including several of the core biosynthetic genes. Finally, to examine the functional effects of genome variation between strains, we measured amylase activity, proteolytic activity, and growth rate on several different substrates. RIB 40 produced significantly higher levels of amylase compared to 14160 when grown on rice and starch. Accordingly, RIB 40 grew faster on rice, while 14160 grew faster on soy. Taken together, our analyses reveal substantial genome and phenotypic variation within A. oryzae.

Population Genomic Analysis of Listeria monocytogenes From Food Reveals Substrate-Specific Genome Variation

Listeria monocytogenes is the major causative agent of the foodborne illness listeriosis. Listeriosis presents as flu-like symptoms in healthy individuals, and can be fatal for children, elderly, pregnant women, and immunocompromised individuals. Estimates suggest that L. monocytogenes results in ∼1,600 illnesses and ∼260 deaths annually in the United States. L. monocytogenes can survive and persist in a variety of harsh environments, including conditions encountered in production of fermented dairy products such as cheese. For instance, microbial growth is often limited in soft cheese fermentation because of harsh pH, water content, and salt concentrations. However, L. monocytogenes has caused a number of deadly listeriosis outbreaks through the contamination of cheese. The purpose of this study was to understand if genetically distinct populations of L. monocytogenes are associated with particular foods, including cheese and dairy. To address this goal, we analyzed the population genetic structure of 504 L. monocytogenes strains isolated from food with publicly available genome assemblies. We identified 10 genetically distinct populations spanning L. monocytogenes lineages 1, II, and III and serotypes 1/2a, 1/2b, 1/2c, 4b, and 4c. We observed an overrepresentation of isolates from specific populations with cheese (population 2), fruit/vegetable (population 2), seafood (populations 5, 8 and 9) and meat (population 10). We used the Large Scale Blast Score Ratio pipeline and Roary to identify genes unique to population 1 and population 2 in comparison with all other populations, and screened for the presence of antimicrobial resistance genes and virulence genes across all isolates. We identified > 40 genes that were present at high frequency in population 1 and population 2 and absent in most other isolates. Many of these genes encoded for transcription factors, and cell surface anchored proteins. Additionally, we found that the virulence genes aut and ami were entirely or partially deleted in population 2. These results indicate that some L. monocytogenes populations may exhibit associations with particular foods, including cheese, and that gene content may contribute to this pattern.

Genome-Wide Association for Itraconazole Sensitivity in Non-resistant Clinical Isolates of Aspergillus fumigatus

Aspergillus fumigatus is a potentially lethal opportunistic pathogen that infects over ~200,000 people and causes ~100,000 deaths per year globally. Treating A. fumigatus infections is particularly challenging because of the recent emergence of azole-resistance. The majority of studies focusing on the molecular mechanisms underlying azole resistance have examined azole-resistant isolates. However, isolates that are susceptible to azoles also display variation in their sensitivity, presenting a unique opportunity to identify genes contributing to azole sensitivity. Here, we used genome-wide association (GWA) analysis to identify loci involved in azole sensitivity by analyzing the association between 68,853 SNPs and itraconazole (ITCZ) minimum inhibitory concentration (MIC) in 76 clinical isolates of A. fumigatus from Japan. Population structure analysis suggests the presence of four distinct populations, with ITCZ MICs distributed relatively evenly across populations. We independently conducted GWA when treating ITCZ MIC as a quantitative trait and a binary trait, and identified two SNPs with strong associations in both analyses. These SNPs fell within the coding regions of Afu2g02220 and Afu2g02140. We functionally validated Afu2g02220 by knocking it out using a CRISPR/Cas9 approach, because orthologs of this gene are involved in sterol modification and ITCZ targets the ergosterol biosynthesis pathway. Knockout strains displayed no difference in growth compared to the parent strain in minimal media, yet a minor but consistent inhibition of growth in the presence of 0.15 μg/ml ITCZ. Our results suggest that GWA paired with efficient gene deletion is a powerful and unbiased strategy for identifying the genetic basis of complex traits in A. fumigatus.

Genomic profiling of bacterial and fungal communities and their predictive functionality during pulque fermentation by whole-genome shotgun sequencing

Pulque is a culturally important 4,000-year-old traditional Mexican fermented drink. Pulque is produced by adding fresh aguamiel (agave sap) to mature pulque, resulting in a mixture of microbial communities and chemical compositions. We performed shotgun metagenomic sequencing of five stages of pulque fermentation to characterize organismal and functional diversity. We identified 6 genera (Acinetobacter, Lactobacillus, Lactococcus, Leuconostoc, Saccharomyces and Zymomonas) and 10 species (Acinetobacter boissieri, Acinetobacter nectaris, Lactobacillus sanfranciscensis, Lactococcus lactis, Lactococcus piscium, Lactococcus plantarum, Leuconostoc citreum, Leuconostoc gelidum, Zymomonas mobilis and Saccharomyces cerevisiae) that were present ≥ 1% in at least one stage of pulque fermentation. The abundance of genera and species changed during fermentation and was associated with a decrease in sucrose and increases in ethanol and lactic acid, suggesting that resource competition shapes organismal diversity. We also predicted functional profiles, based on organismal gene content, for each fermentation stage and identified an abundance of genes associated with the biosynthesis of folate, an essential B-vitamin. Additionally, we investigated the evolutionary relationships of S. cerevisiae and Z. mobilis, two of the major microbial species found in pulque. For S. cerevisiae, we used a metagenomics assembly approach to identify S. cerevisiae scaffolds from pulque, and performed phylogenetic analysis of these sequences along with a collection of 158 S. cerevisiae strains. This analysis suggests that S. cerevisiae from pulque is most closely related to Asian strains isolated from sake and bioethanol. Lastly, we isolated and sequenced the whole-genomes of three strains of Z. mobilis from pulque and compared their relationship to seven previously sequenced isolates. Our results suggest pulque strains may represent a distinct lineage of Z. mobilis.

Controlling aflatoxin contamination and propagation of Aspergillus flavus by a soy-fermenting Aspergillus oryzae strain

Aflatoxins (AFs) are a group of carcinogenic and immunosuppressive mycotoxins that threaten global food safety. Globally, over 4.5 billion people are exposed to unmonitored levels of AFs. Aspergillus flavus is the major source of AF contamination in agricultural crops. One approach to reduce levels of AFs in agricultural commodities is to apply a non-aflatoxigenic competitor, e.g., Afla-Guard, to crop fields. In this study, we demonstrate that the food fermenting Aspergillus oryzae M2040 strain, isolated from Korean Meju (a brick of dry-fermented soybeans), can inhibit aflatoxin B1 (AFB1) production and proliferation of toxigenic A. flavus in lab culture conditions and peanuts. In peanuts, 1% inoculation level of A. oryzae M2040 could effectively displace the toxigenic A. flavus and inhibit AFB1 production. Moreover, cell-free culture filtrate of A. oryzae M2040 effectively inhibited AFB1 production and A. flavus growth, suggesting A. oryzae M2040 secretes inhibitory compounds. Whole genome-based comparative analyses indicate that the A. oryzae M2040 and Afla-Guard genomes are 37.9 and 36.4 Mbp, respectively, with each genome containing ~100 lineage specific genes. Our study establishes the idea of using A. oryzae and/or its cell-free culture fermentate as a potent biocontrol agent to control A. flavus propagation and AF contamination.

A population genomic characterization of copy number variation in the opportunistic fungal pathogen Aspergillus fumigatus

Aspergillus fumigatus is a potentially deadly opportunistic fungal pathogen. Molecular studies have shaped our understanding of the genes, proteins, and molecules that contribute to A. fumigatus pathogenicity, but few studies have characterized genome-wide patterns of genetic variation at the population level. Of A. fumigatus genomic studies to-date, most focus mainly on single nucleotide polymorphisms and large structural variants, while overlooking the contribution of copy number variation (CNV). CNV is a class of small structural variation defined as loci that vary in their number of copies between individuals due to duplication, gain, or deletion. CNV can influence phenotype, including fungal virulence. In the present study, we characterized the population genomic patterns of CNV in a diverse collection of 71 A. fumigatus isolates using publicly available sequencing data. We used genome-wide single nucleotide polymorphisms to infer the population structure of these isolates and identified three populations consisting of at least 8 isolates. We then computationally predicted genome-wide CNV profiles for each isolate and conducted analyses at the species-, population-, and individual levels. Our results suggest that CNV contributes to genetic variation in A. fumigatus, with ~10% of the genome being CN variable. Our analysis indicates that CNV is non-randomly distributed across the A. fumigatus genome, and is overrepresented in subtelomeric regions. Analysis of gene ontology categories in genes that overlapped CN variants revealed an enrichment of genes related to transposable element and secondary metabolism functions. We further identified 72 loci containing 33 genes that showed divergent copy number profiles between the three A. fumigatus populations. Many of these genes encode proteins that interact with the cell surface or are involved in pathogenicity. Our results suggest that CNV is an important source of genetic variation that could account for some of the phenotypic differences between A. fumigatus populations and isolates.

Immunomodulators targeting MARCO expression improve resistance to postinfluenza bacterial pneumonia

Downregulation of the alveolar macrophage (AM) receptor with collagenous structure (MARCO) leads to susceptibility to postinfluenza bacterial pneumonia, a major cause of morbidity and mortality. We sought to determine whether immunomodulation of MARCO could improve host defense and resistance to secondary bacterial pneumonia. RNAseq analysis identified a striking increase in MARCO expression between days 9 and 11 after influenza infection and indicated important roles for Akt and Nrf2 in MARCO recovery. In vitro, primary human AM-like monocyte-derived macrophages (AM-MDMs) and THP-1 macrophages were treated with IFNγ to model influenza effects. Activators of Nrf2 (sulforaphane) or Akt (SC79) caused increased MARCO expression and a MARCO-dependent improvement in phagocytosis in IFNγ-treated cells and improved survival in mice with postinfluenza pneumococcal pneumonia. Transcription factor analysis also indicated a role for transcription factor E-box (TFEB) in MARCO recovery. Overexpression of TFEB in THP-1 cells led to marked increases in MARCO. The ability of Akt activation to increase MARCO expression in IFNγ-treated AM-MDMs was abrogated in TFEB-knockdown cells, indicating Akt increases MARCO expression through TFEB. Increasing MARCO expression by targeting Nrf2 signaling or the Akt-TFEB-MARCO pathway are promising strategies to improve bacterial clearance and survival in postinfluenza bacterial pneumonia.

Copy number variation contributes to cryptic genetic variation in outbreak lineages of Cryptococcus gattii from the North American Pacific Northwest

Background

Copy number variants (CNVs) are a class of structural variants (SVs) and are defined as fragments of DNA that are present at variable copy number in comparison with a reference genome. Recent advances in bioinformatics methodologies and sequencing technologies have enabled the high-resolution quantification of genome-wide CNVs. In pathogenic fungi SVs have been shown to alter gene expression, influence host specificity, and drive fungicide resistance, but little attention has focused specifically on CNVs. Using publicly available sequencing data, we identified 90 isolates across 212 Cryptococcus gattii genomes that belong to the VGII subgroups responsible for the recent deadly outbreaks in the North American Pacific Northwest. We generated CNV profiles for each sample to investigate the prevalence and function of CNV in C. gattii.

Results

We identified eight genetic clusters among publicly available Illumina whole genome sequence data from 212 C. gattii isolates through population structure analysis. Three clusters represent the VGIIa, VGIIb, and VGIIc subgroups from the North American Pacific Northwest. CNV was bioinformatically predicted and affected ~300–400 Kilobases (Kb) of the C. gattii VGII subgroup genomes. Sixty-seven loci, encompassing 58 genes, showed highly divergent patterns of copy number variation between VGII subgroups. Analysis of PFam domains within divergent CN variable genes revealed enrichment of protein domains associated with transport, cell wall organization and external encapsulating structure.

Conclusions

CNVs may contribute to pathological and phenotypic differences observed between the C. gattii VGIIa, VGIIb, and VGIIc subpopulations. Genes overlapping with population differentiated CNVs were enriched for several virulence related functional terms. These results uncover novel candidate genes to examine the genetic and functional underpinnings of C. gattii pathogenicity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3044-0) contains supplementary material, which is available to authorized users.

Evolution of a Heavy Metal Homeostasis/Resistance Island Reflects Increasing Copper Stress in Enterobacteria

Copper homeostasis in bacteria is challenged by periodic elevation of copper levels in the environment, arising from both natural sources and human inputs. Several mechanisms have evolved to efflux copper from bacterial cells, including thecus(copper sensing copper efflux system), andpco(plasmid-borne copper resistance system) systems. The genes belonging to these two systems can be physically clustered in a Copper Homeostasis and Silver Resistance Island (CHASRI) on both plasmids and chromosomes in Enterobacteria. Increasing use of copper in agricultural and industrial applications raises questions about the role of human activity in the evolution of novel copper resistance mechanisms. Here we present evidence that CHASRI emerged and diversified in response to copper deposition across aerobic and anaerobic environments. An analysis of diversification rates and a molecular clock model suggest that CHASRI experienced repeated episodes of elevated diversification that could correspond to peaks in human copper production. Phylogenetic analyses suggest that CHASRI originated in a relative ofEnterobacter cloacaeas the ultimate product of sequential assembly of several pre-existing two-gene modules. Once assembled, CHASRI dispersed via horizontal gene transfer within Enterobacteriaceae and also to certain members of Shewanellaceae, where the originalpcomodule was replaced by a divergentpcohomolog. Analyses of copper stress mitigation suggest that CHASRI confers increased resistance aerobically, anaerobically, and during shifts between aerobic and anaerobic environments, which could explain its persistence in facultative anaerobes and emergent enteric pathogens.

The genomics of microbial domestication in the fermented food environment

Shortly after the agricultural revolution, the domestication of bacteria, yeasts, and molds, played an essential role in enhancing the stability, quality, flavor, and texture of food products. These domestication events were probably the result of human food production practices that entailed the continual recycling of isolated microbial communities in the presence of abundant agricultural food sources. We suggest that within these novel agrarian food niches the metabolic requirements of those microbes became regular and predictable resulting in rapid genomic specialization through such mechanisms as pseudogenization, genome decay, interspecific hybridization, gene duplication, and horizontal gene transfer. The ultimate result was domesticated strains of microorganisms with enhanced fermentative capacities.

Investigation of Aspergillus fumigatus biofilm formation by various "omics" approaches

In the lung, Aspergillus fumigatus usually forms a dense colony of filaments embedded in a polymeric extracellular matrix called biofilm (BF). This extracellular matrix embeds and glues hyphae together and protects the fungus from an outside hostile environment. This extracellular matrix is absent in fungal colonies grown under classical liquid shake conditions (PL), which were historically used to understand A. fumigatus pathobiology. Recent works have shown that the fungus in this aerial grown BF-like state exhibits reduced susceptibility to antifungal drugs and undergoes major metabolic changes that are thought to be associated to virulence. These differences in pathological and physiological characteristics between BF and liquid shake conditions suggest that the PL condition is a poor in vitro disease model. In the laboratory, A. fumigatus mycelium embedded by the extracellular matrix can be produced in vitro in aerial condition using an agar-based medium. To provide a global and accurate understanding of A. fumigatus in vitro BF growth, we utilized microarray, RNA-sequencing, and proteomic analysis to compare the global gene and protein expression profiles of A. fumigatus grown under BF and PL conditions. In this review, we will present the different signatures obtained with these three “omics” methods. We will discuss the advantages and limitations of each method and their complementarity.

The diverse applications of RNA-seq for functional genomic studies in Aspergillus fumigatus

The deep sequencing of an mRNA population, RNA-seq, is a very successful application of next-generation sequencing technologies (NGSTs). RNA-seq takes advantage of two key NGST features: (1) samples can be mixtures of different DNA pieces, and (2) sequencing provides both qualitative and quantitative information about each DNA piece analyzed. We recently used RNA-seq to study the transcriptome of Aspergillus fumigatus, a deadly human fungal pathogen. Analysis of the RNA-seq data indicates that there are likely tens of unannotated and hundreds of novel genes in the A. fumigatus transcriptome, mostly encoding for small proteins. Inspection of transcriptome-wide variation between two isolates reveals thousands of single nucleotide polymorphisms. Finally, comparison of the transcriptome profiles of one isolate in two different growth conditions identified thousands of differentially expressed genes. These results demonstrate the utility and potential of RNA-seq for functional genomics studies in A. fumigatus and other fungal human pathogens.

A bioinformatics approach for integrated transcriptomic and proteomic comparative analyses of model and non-sequenced anopheline vectors of human malaria parasites

Malaria morbidity and mortality caused by both Plasmodium falciparum and Plasmodium vivax extend well beyond the African continent, and although P. vivax causes between 80 and 300 million severe cases each year, vivax transmission remains poorly understood. Plasmodium parasites are transmitted by Anopheles mosquitoes, and the critical site of interaction between parasite and host is at the mosquito's luminal midgut brush border. Although the genome of the “model” African P. falciparum vector, Anopheles gambiae, has been sequenced, evolutionary divergence limits its utility as a reference across anophelines, especially non-sequenced P. vivax vectors such as Anopheles albimanus. Clearly, technologies and platforms that bridge this substantial scientific gap are required in order to provide public health scientists with key transcriptomic and proteomic information that could spur the development of novel interventions to combat this disease. To our knowledge, no approaches have been published that address this issue. To bolster our understanding of P. vivax–An. albimanus midgut interactions, we developed an integrated bioinformatic-hybrid RNA-Seq-LC-MS/MS approach involving An. albimanus transcriptome (15,764 contigs) and luminal midgut subproteome (9,445 proteins) assembly, which, when used with our custom Diptera protein database (685,078 sequences), facilitated a comparative proteomic analysis of the midgut brush borders of two important malaria vectors, An. gambiae and An. albimanus.

The function and evolution of the Aspergillus genome

Species in the filamentous fungal genus Aspergillus display a wide diversity of lifestyles and are of great importance to humans. The decoding of genome sequences from a dozen species that vary widely in their degree of evolutionary affinity has galvanized studies of the function and evolution of the Aspergillus genome in clinical, industrial, and agricultural environments. Here, we synthesize recent key findings that shed light on the architecture of the Aspergillus genome, on the molecular foundations of the genus' astounding dexterity and diversity in secondary metabolism, and on the genetic underpinnings of virulence in Aspergillus fumigatus, one of the most lethal fungal pathogens. Many of these insights dramatically expand our knowledge of fungal and microbial eukaryote genome evolution and function and argue that Aspergillus constitutes a superb model clade for the study of functional and comparative genomics.

The evolutionary imprint of domestication on genome variation and function of the filamentous fungus Aspergillus oryzae

The domestication of animals, plants, and microbes fundamentally transformed the lifestyle and demography of the human species [1]. Although the genetic and functional underpinnings of animal and plant domestication are well understood, little is known about microbe domestication [2-6]. Here, we systematically examined genome-wide sequence and functional variation between the domesticated fungus Aspergillus oryzae, whose saccharification abilities humans have harnessed for thousands of years to produce sake, soy sauce, and miso from starch-rich grains, and its wild relative A. flavus, a potentially toxigenic plant and animal pathogen [7]. We discovered dramatic changes in the sequence variation and abundance profiles of genes and wholesale primary and secondary metabolic pathways between domesticated and wild relative isolates during growth on rice. Our data suggest that, through selection by humans, an atoxigenic lineage of A. flavus gradually evolved into a "cell factory" for enzymes and metabolites involved in the saccharification process. These results suggest that whereas animal and plant domestication was largely driven by Neolithic "genetic tinkering" of developmental pathways, microbe domestication was driven by extensive remodeling of metabolism.

Transcriptome of the adult female malaria mosquito vector Anopheles albimanus

BACKGROUND

Human Malaria is transmitted by mosquitoes of the genus Anopheles. Transmission is a complex phenomenon involving biological and environmental factors of humans, parasites and mosquitoes. Among more than 500 anopheline species, only a few species from different branches of the mosquito evolutionary tree transmit malaria, suggesting that their vectorial capacity has evolved independently. Anopheles albimanus (subgenus Nyssorhynchus) is an important malaria vector in the Americas. The divergence time between Anopheles gambiae, the main malaria vector in Africa, and the Neotropical vectors has been estimated to be 100 My. To better understand the biological basis of malaria transmission and to develop novel and effective means of vector control, there is a need to explore the mosquito biology beyond the An. gambiae complex.

RESULTS

We sequenced the transcriptome of the An. albimanus adult female. By combining Sanger, 454 and Illumina sequences from cDNA libraries derived from the midgut, cuticular fat body, dorsal vessel, salivary gland and whole body, we generated a single, high-quality assembly containing 16,669 transcripts, 92% of which mapped to the An. darlingi genome and covered 90% of the core eukaryotic genome. Bidirectional comparisons between the An. gambiae, An. darlingi and An. albimanus predicted proteomes allowed the identification of 3,772 putative orthologs. More than half of the transcripts had a match to proteins in other insect vectors and had an InterPro annotation. We identified several protein families that may be relevant to the study of Plasmodium-mosquito interaction. An open source transcript annotation browser called GDAV (Genome-Delinked Annotation Viewer) was developed to facilitate public access to the data generated by this and future transcriptome projects.

CONCLUSIONS

We have explored the adult female transcriptome of one important New World malaria vector, An. albimanus. We identified protein-coding transcripts involved in biological processes that may be relevant to the Plasmodium lifecycle and can serve as the starting point for searching targets for novel control strategies. Our data increase the available genomic information regarding An. albimanus several hundred-fold, and will facilitate molecular research in medical entomology, evolutionary biology, genomics and proteomics of anopheline mosquito vectors. The data reported in this manuscript is accessible to the community via the VectorBase website (http://www.vectorbase.org/Other/AdditionalOrganisms/).

Evidence for genetic differentiation and variable recombination rates among Dutch populations of the opportunistic human pathogen Aspergillus fumigatus

As the frequency of antifungal drug resistance continues to increase, understanding the genetic structure of fungal populations, where resistant isolates have emerged and spread, is of major importance. Aspergillus fumigatus is an ubiquitously distributed fungus and the primary causative agent of invasive aspergillosis (IA), a potentially lethal infection in immunocompromised individuals. In the last few years, an increasing number of A. fumigatus isolates has evolved resistance to triazoles, the primary drugs for treating IA infections. In most isolates, this multiple-triazole-resistance (MTR) phenotype is caused by mutations in the cyp51A gene, which encodes the protein targeted by the triazoles. We investigated the genetic differentiation and reproductive mode of A. fumigatus in the Netherlands, the country where the MTR phenotype probably originated, to determine their role in facilitating the emergence and distribution of resistance genotypes. Using 20 genome-wide neutral markers, we genotyped 255 Dutch isolates including 25 isolates with the MTR phenotype. In contrast to previous reports, our results show that Dutch A. fumigatus genotypes are genetically differentiated into five distinct populations. Four of the five populations show significant linkage disequilibrium, indicative of an asexual reproductive mode, whereas the fifth population is in linkage equilibrium, indicative of a sexual reproductive mode. Notably, the observed genetic differentiation among Dutch isolates does not correlate with geography, although all isolates with the MTR phenotype nest within a single, predominantly asexual, population. These results suggest that both reproductive mode and genetic differentiation contribute to the structure of Dutch A. fumigatus populations and are probably shaping the evolutionary dynamics of drug resistance in this potentially deadly pathogen.

Complete bacteriophage transfer in a bacterial endosymbiont (Wolbachia) determined by targeted genome capture

Bacteriophage flux can cause the majority of genetic diversity in free-living bacteria. This tenet of bacterial genome evolution generally does not extend to obligate intracellular bacteria owing to their reduced contact with other microbes and a predominance of gene deletion over gene transfer. However, recent studies suggest intracellular coinfections in the same host can facilitate exchange of mobile elements between obligate intracellular bacteria—a means by which these bacteria can partially mitigate the reductive forces of the intracellular lifestyle. To test whether bacteriophages transfer as single genes or larger regions between coinfections, we sequenced the genome of the obligate intracellular Wolbachia strain wVitB from the parasitic wasp Nasonia vitripennis and compared it against the prophage sequences of the divergent wVitA coinfection. We applied, for the first time, a targeted sequence capture array to specifically trap the symbiont's DNA from a heterogeneous mixture of eukaryotic, bacterial, and viral DNA. The tiled array successfully captured the genome with 98.3% efficiency. Examination of the genome sequence revealed the largest transfer of bacteriophage and flanking genes (52.2 kb) to date between two obligate intracellular coinfections. The mobile element transfer occurred in the recent evolutionary past based on the 99.9% average nucleotide identity of the phage sequences between the two strains. In addition to discovering an evolutionary recent and large-scale horizontal phage transfer between coinfecting obligate intracellular bacteria, we demonstrate that “targeted genome capture” can enrich target DNA to alleviate the problem of isolating symbiotic microbes that are difficult to culture or purify from the conglomerate of organisms inside eukaryotes.

Benchmarking next-generation transcriptome sequencing for functional and evolutionary genomics

Next-generation sequencing has opened the door to genomic analysis of nonmodel organisms. Technologies generating long-sequence reads (200-400 bp) are increasingly used in evolutionary studies of nonmodel organisms, but the short-sequence reads (30-50 bp) that can be produced at lower cost are thought to be of limited utility for de novo sequencing applications. Here, we tested this assumption by short-read sequencing the transcriptomes of the tropical disease vectors Aedes aegypti and Anopheles gambiae, for which complete genome sequences are available. Comparison of our results to the reference genomes allowed us to accurately evaluate the quantity, quality, and functional and evolutionary information content of our "test" data. We produced more than 0.7 billion nucleotides of sequenced data per species that assembled into more than 21,000 test contigs larger than 100 bp per species and covered approximately 27% of the Aedes reference transcriptome. Remarkably, the substitution error rate in the test contigs was approximately 0.25% per site, with very few indels or assembly errors. Test contigs of both species were enriched for genes involved in energy production and protein synthesis and underrepresented in genes involved in transcription and differentiation. Ortholog prediction using the test contigs was accurate across hundreds of millions of years of evolution. Our results demonstrate the considerable utility of short-read transcriptome sequencing for genomic studies of nonmodel organisms and suggest an approach for assessing the information content of next-generation data for evolutionary studies.

Comparative and functional characterization of intragenic tandem repeats in 10 Aspergillus genomes

Intragenic tandem repeats (ITRs) are consecutive repeats of three or more nucleotides found in coding regions. ITRs are the underlying cause of several human genetic diseases and have been associated with phenotypic variation, including pathogenesis, in several clades of the tree of life. We have examined the evolution and functional role of ITRs in 10 genomes spanning the fungal genus Aspergillus, a clade of relevance to medicine, agriculture, and industry. We identified several hundred ITRs in each of the species examined. ITR content varied extensively between species, with an average 79% of ITRs unique to a given species. For the fraction of conserved ITR regions, sequence comparisons within species and between close relatives revealed that they were highly variable. ITR-containing proteins were evolutionarily less conserved, compositionally distinct, and overrepresented for domains associated with cell-surface localization and function relative to the rest of the proteome. Furthermore, ITRs were preferentially found in proteins involved in transcription, cellular communication, and cell-type differentiation but were underrepresented in proteins involved in metabolism and energy. Importantly, although ITRs were evolutionarily labile, their functional associations appeared. To be remarkably conserved across eukaryotes. Fungal ITRs likely participate in a variety of developmental processes and cell-surface-associated functions, suggesting that their contribution to fungal lifestyle and evolution may be more general than previously assumed.

Estimation of body water compartments in cirrhosis by multiple-frequency bioelectrical-impedance analysis

Estimation of total body water by measuring bioelectrical impedance at a fixed frequency of 50 kHz is useful in assessing body composition in healthy populations. However, in cirrhosis, the distribution of total body water between the extracellular and intracellular compartments is of greater clinical importance. We report an evaluation of a new multiple-frequency bioelectrical-impedance analysis technique (MFBIA) that may quantify the distribution of total body water in cirrhosis. In 21 cirrhotic patients and 21 healthy control subjects, impedance to the flow of current was measured at frequencies ranging from 4 to 1012 kHz. These measurements were used to estimate body water compartments and then compared with total body water and extracellular water determined by isotope methodology. In cirrhotic patients, extracellular water and total body water (as determined by isotope methods) were well predicted by MFBIA (r = 0.73 and 0.89, respectively). However, the 95% confidence intervals of the limits of agreement between MFBIA and the isotope methods were +/-14% and +/-9% for cirrhotics (extracellular water and total body water, respectively) and +/-9% and +/-9% for cirrhotics without ascites. The 95% confidence intervals estimated from the control group were +/-10% and +/-5% for extracellular water and total body water, respectively. Thus, despite strong correlations between MFBIA and isotope measurements, the relatively large limits of agreement with accepted techniques suggest that the MFBIA technique requires further refinement before it can be routinely used to determine the nutritional assessment of individual cirrhotic patients.