Optimizing Illumina next-generation sequencing library preparation for extremely AT-biased genomes.

BAckground: Massively parallel sequencing technology is revolutionizing approaches to genomic and genetic research. Since its advent, the scale and efficiency of Next-Generation Sequencing (NGS) has rapidly improved. In spite of this success, sequencing genomes or genomic regions with extremely biased base composition is still a great challenge to the currently available NGS platforms. The genomes of some important pathogenic organisms like Plasmodium falciparum (high AT content) and Mycobacterium tuberculosis (high GC content) display extremes of base composition. The standard library preparation procedures that employ PCR amplification have been shown to cause uneven read coverage particularly across AT and GC rich regions, leading to problems in genome assembly and variation analyses. Alternative library-preparation approaches that omit PCR amplification require large quantities of starting material and hence are not suitable for small amounts of DNA/RNA such as those from clinical isolates. We have developed and optimized library-preparation procedures suitable for low quantity starting material and tolerant to extremely high AT content sequences. Results: We have used our optimized conditions in parallel with standard methods to prepare Illumina sequencing libraries from a non-clinical and a clinical isolate (containing ~53% host contamination). By analyzing and comparing the quality of sequence data generated, we show that our optimized conditions that involve a PCR additive (TMAC), produces amplified libraries with improved coverage of extremely AT-rich regions and reduced bias toward GC neutral templates. Conclusion: We have developed a robust and optimized Next-Generation Sequencing library amplification method suitable for extremely AT-rich genomes. The new amplification conditions significantly reduce bias and retain the complexity of either extremes of base composition. This development will greatly benefit sequencing clinical samples that often require amplification due to low mass of DNA starting material

In silico prediction of candidate gene targets for the management of African cassava whitefly (Bemisia tabaci, SSA1-SG1), a key vector of viruses causing cassava brown streak disease

Whiteflies (Bemisia tabaci sensu lato) have a wide host range and are globally important agricultural pests. In Sub-Saharan Africa, they vector viruses that cause two ongoing disease epidemics: cassava brown streak disease and cassava mosaic virus disease. These two diseases threaten food security for more than 800 million people in Sub-Saharan Africa. Efforts are ongoing to identify target genes for the development of novel management options against the whitefly populations that vector these devastating viral diseases affecting cassava production in Sub-Saharan Africa. This study aimed to identify genes that mediate osmoregulation and symbiosis functions within cassava whitefly gut and bacteriocytes and evaluate their potential as key gene targets for novel whitefly control strategies. The gene expression profiles of dissected guts, bacteriocytes and whole bodies were compared by RNAseq analysis to identify genes with significantly enriched expression in the gut and bacteriocytes. Phylogenetic analyses identified three candidate osmoregulation gene targets: two α-glucosidases, SUC 1 and SUC 2 with predicted function in sugar transformations that reduce osmotic pressure in the gut; and a water-specific aquaporin (AQP1) mediating water cycling from the distal to the proximal end of the gut. Expression of the genes in the gut was enriched 23.67-, 26.54- and 22.30-fold, respectively. Genome-wide metabolic reconstruction coupled with constraint-based modeling revealed four genes (argH, lysA, BCAT & dapB) within the bacteriocytes as potential targets for the management of cassava whiteflies. These genes were selected based on their role and essentiality within the different essential amino acid biosynthesis pathways. A demonstration of candidate osmoregulation and symbiosis gene targets in other species of the Bemisia tabaci species complex that are orthologs of the empirically validated osmoregulation genes highlights the latter as promising gene targets for the control of cassava whitefly pests by in planta RNA interference

An optimized microarray platform for assaying genomic variation in Plasmodium falciparum field populations

We present an optimized probe design for copy number variation (CNV) and SNP genotyping in the Plasmodium falciparum genome. We demonstrate that variable length and isothermal probes are superior to static length probes. We show that sample preparation and hybridization conditions mitigate the effects of host DNA contamination in field samples. The microarray and workflow presented can be used to identify CNVs and SNPs with 95% accuracy in a single hybridization, in field samples containing up to 92% human DNA contamination

Drug-resistant genotypes and multi-clonality in Plasmodium falciparum analysed by direct genome sequencing from peripheral blood of malaria patients.

Naturally acquired blood-stage infections of the malaria parasite Plasmodium falciparum typically harbour multiple haploid clones. The apparent number of clones observed in any single infection depends on the diversity of the polymorphic markers used for the analysis, and the relative abundance of rare clones, which frequently fail to be detected among PCR products derived from numerically dominant clones. However, minority clones are of clinical interest as they may harbour genes conferring drug resistance, leading to enhanced survival after treatment and the possibility of subsequent therapeutic failure. We deployed new generation sequencing to derive genome data for five non-propagated parasite isolates taken directly from 4 different patients treated for clinical malaria in a UK hospital. Analysis of depth of coverage and length of sequence intervals between paired reads identified both previously described and novel gene deletions and amplifications. Full-length sequence data was extracted for 6 loci considered to be under selection by antimalarial drugs, and both known and previously unknown amino acid substitutions were identified. Full mitochondrial genomes were extracted from the sequencing data for each isolate, and these are compared against a panel of polymorphic sites derived from published or unpublished but publicly available data. Finally, genome-wide analysis of clone multiplicity was performed, and the number of infecting parasite clones estimated for each isolate. Each patient harboured at least 3 clones of P. falciparum by this analysis, consistent with results obtained with conventional PCR analysis of polymorphic merozoite antigen loci. We conclude that genome sequencing of peripheral blood P. falciparum taken directly from malaria patients provides high quality data useful for drug resistance studies, genomic structural analyses and population genetics, and also robustly represents clonal multiplicity

Advancing vector biology research: a community survey for future directions, research applications and infrastructure requirements

Vector-borne pathogens impact public health, animal production, and animal welfare. Research on arthropod vectors such as mosquitoes, ticks, sandflies, and midges which transmit pathogens to humans and economically important animals is crucial for development of new control measures that target transmission by the vector. While insecticides are an important part of this arsenal, appearance of resistance mechanisms is increasingly common. Novel tools for genetic manipulation of vectors, use of Wolbachia endosymbiotic bacteria, and other biological control mechanisms to prevent pathogen transmission have led to promising new intervention strategies, adding to strong interest in vector biology and genetics as well as vector-pathogen interactions. Vector research is therefore at a crucial juncture, and strategic decisions on future research directions and research infrastructure investment should be informed by the research community. A survey initiated by the European Horizon 2020 INFRAVEC-2 consortium set out to canvass priorities in the vector biology research community and to determine key activities that are needed for researchers to efficiently study vectors, vector-pathogen interactions, as well as access the structures and services that allow such activities to be carried out. We summarize the most important findings of the survey which in particular reflect the priorities of researchers in European countries, and which will be of use to stakeholders that include researchers, government, and research organizations

What is new in FungiDB: a web-based bioinformatics platform for omics-scale data analysis for fungal and oomycete species

FungiDB (https://fungidb.org) serves as a valuable online resource that seamlessly integrates genomic and related large-scale data for a wide range of fungal and oomycete species. As an integral part of the VEuPathDB Bioinformatics Resource Center (https://veupathdb.org), FungiDB continually integrates both published and unpublished data addressing various aspects of fungal biology. Established in early 2011, the database has evolved to support 674 datasets. The datasets include over 300 genomes spanning various taxa (e.g. Ascomycota, Basidiomycota, Blastocladiomycota, Chytridiomycota, Mucoromycota, as well as Albuginales, Peronosporales, Pythiales, and Saprolegniales). In addition to genomic assemblies and annotation, over 300 extra datasets encompassing diverse information, such as expression and variation data, are also available. The resource also provides an intuitive web-based interface, facilitating comprehensive approaches to data mining and visualization. Users can test their hypotheses and navigate through omics-scale datasets using a built-in search strategy system. Moreover, FungiDB offers capabilities for private data analysis via the integrated VEuPathDB Galaxy platform. FungiDB also permits genome improvements by capturing expert knowledge through the User Comments system and the Apollo genome annotation editor for structural and functional gene curation. FungiDB facilitates data exploration and analysis and contributes to advancing research efforts by capturing expert knowledge for fungal and oomycete species

An Effective Method to Purify Plasmodium falciparum DNA Directly from Clinical Blood Samples for Whole Genome High-Throughput Sequencing

Highly parallel sequencing technologies permit cost-effective whole genome sequencing of hundreds of Plasmodium parasites. The ability to sequence clinical Plasmodium samples, extracted directly from patient blood without a culture step, presents a unique opportunity to sample the diversity of “natural” parasite populations in high resolution clinical and epidemiological studies. A major challenge to sequencing clinical Plasmodium samples is the abundance of human DNA, which may substantially reduce the yield of Plasmodium sequence. We tested a range of human white blood cell (WBC) depletion methods on P. falciparum-infected patient samples in search of a method displaying an optimal balance of WBC-removal efficacy, cost, simplicity, and applicability to low resource settings. In the first of a two-part study, combinations of three different WBC depletion methods were tested on 43 patient blood samples in Mali. A two-step combination of Lymphoprep plus Plasmodipur best fitted our requirements, although moderate variability was observed in human DNA quantity. This approach was further assessed in a larger sample of 76 patients from Burkina Faso. WBC-removal efficacy remained high (<30% human DNA in >70% samples) and lower variation was observed in human DNA quantities. In order to assess the Plasmodium sequence yield at different human DNA proportions, 59 samples with up to 60% human DNA contamination were sequenced on the Illumina Genome Analyzer platform. An average ∼40-fold coverage of the genome was observed per lane for samples with ≤30% human DNA. Even in low resource settings, using a simple two-step combination of Lymphoprep plus Plasmodipur, over 70% of clinical sample preparations should exhibit sufficiently low human DNA quantities to enable ∼40-fold sequence coverage of the P. falciparum genome using a single lane on the Illumina Genome Analyzer platform. This approach should greatly facilitate large-scale clinical and epidemiologic studies of P. falciparum

Publisher Correction: The genome of the stable fly, Stomoxys calcitrans, reveals potential mechanisms underlying reproduction, host interactions, and novel targets for pest control (BMC Biology, (2021), 19, 1, (41), 10.1186/s12915-021-00975-9)

Following publication of the original article [1], it was reported that the article copyright was incorrect. The correct copyright statement is: © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2021. The original article [1] has been corrected

Characterization of Within-Host Plasmodium falciparum Diversity Using Next-Generation Sequence Data

Our understanding of the composition of multi-clonal malarial infections and the epidemiological factors which shape their diversity remain poorly understood. Traditionally within-host diversity has been defined in terms of the multiplicity of infection (MOI) derived by PCR-based genotyping. Massively parallel, single molecule sequencing technologies now enable individual read counts to be derived on genome-wide datasets facilitating the development of new statistical approaches to describe within-host diversity. In this class of measures the FWS metric characterizes within-host diversity and its relationship to population level diversity. Utilizing P. falciparum field isolates from patients in West Africa we here explore the relationship between the traditional MOI and FWS approaches. FWS statistics were derived from read count data at 86,158 SNPs in 64 samples sequenced on the Illumina GA platform. MOI estimates were derived by PCR at the msp-1 and -2 loci. Significant correlations were observed between the two measures, particularly with the msp-1 locus (P = 5.92×10−5). The FWS metric should be more robust than the PCR-based approach owing to reduced sensitivity to potential locus-specific artifacts. Furthermore the FWS metric captures information on a range of parameters which influence out-crossing risk including the number of clones (MOI), their relative proportions and genetic divergence. This approach should provide novel insights into the factors which correlate with, and shape within-host diversity

Comparative Genomic Analysis of six Glossina Genomes, Vectors of African Trypanosomes

Background: Tsetse flies (Glossina sp.) are the vectors of human and animal trypanosomiasis throughout subSaharan Africa. Tsetse flies are distinguished from other Diptera by unique adaptations, including lactation and the birthing of live young (obligate viviparity), a vertebrate blood-specific diet by both sexes, and obligate bacterial symbiosis. This work describes the comparative analysis of six Glossina genomes representing three sub-genera: Morsitans (G. morsitans morsitans, G. pallidipes, G. austeni), Palpalis (G. palpalis, G. fuscipes), and Fusca (G. brevipalpis) which represent different habitats, host preferences, and vectorial capacity. Results: Genomic analyses validate established evolutionary relationships and sub-genera. Syntenic analysis of Glossina relative to Drosophila melanogaster shows reduced structural conservation across the sex-linked X chromosome. Sex-linked scaffolds show increased rates of female-specific gene expression and lower evolutionary rates relative to autosome associated genes. Tsetse-specific genes are enriched in protease, odorant-binding, and helicase activities. Lactation-associated genes are conserved across all Glossina species while male seminal proteins are rapidly evolving. Olfactory and gustatory genes are reduced across the genus relative to other insects. Visionassociated Rhodopsin genes show conservation of motion detection/tracking functions and variance in the Rhodopsin detecting colors in the blue wavelength ranges. Conclusions: Expanded genomic discoveries reveal the genetics underlying Glossina biology and provide a rich body of knowledge for basic science and disease control. They also provide insight into the evolutionary biology underlying novel adaptations and are relevant to applied aspects of vector control such as trap design and discovery of novel pest and disease control strategies