Automated high-throughput probe production for DNA microarray analysis

DNA microarrays have become an established tool for gene expression profiling. Construction of these microarrays using immobilized cDNAs is a common experimental strategy. However, this is extremely laborious, requiring the preparation of hundreds or thousands of cDNA probes. To minimize this initial bottleneck, we developed a comprehensive high-throughput robotic system to prepare DNA probes suitable for microarray analysis with minimal user intervention. We describe an automated system using the MultiPROBE Nucleic Acid Purification Workstation to provide the liquid handling and other functions needed to optimize this process. We were able to carry out fully automated plasmid cDNA isolation, PCR assay setup, and PCR purification and also to direct the characterization and tracking of DNA probes during processing. Protocols began with the initial preparation of a plasmid DNA archive of bacterial stocks in parallel 96-well plates (192 samples/run) and continued through to the dilution and reformatting of chip-ready DNA probes in 384-well format. These and other probe production procedures and additional instrument systems were used to process fully a set of mouse cDNA clones that were then validated by differential gene expression analysis.     

Streamlined Purification of Plasmid DNA From Prokaryotic Cultures

We describe the complete process of AcroPrep Advance Filter Plates for 96 plasmid preparations, starting from prokaryotic culture and ending with high purity DNA. Based on multi-well filtration for bacterial lysate clearance and DNA purification, this method creates a streamlined process for plasmid preparation. Filter plates containing silica-based media can easily be processed by vacuum filtration or centrifuge to yield appreciable quantities of plasmid DNA. Quantitative analyses determine the purified plasmid DNA is consistently of high quality with average OD_260/280 ratios of 1.97. Overall, plasmid yields offer more pure DNA for downstream applications, such as sequencing and cloning. This streamlined method of using AcroPrep Advance Filter Plates allows for manual, semi-automated or fully-automated processing.     

A system of rapid isolation of end-DNA from a small amount of fosmid DNA, with vector-based PCR for chromosome walking.

The pBAC 108L and pFos 1 vectors were developed as stable propagation vectors which, due to their extremely low copy number, facilitate the cloning of a large-sized insert containing repeated DNA. However, the low copy number requires laborious end-DNA preparation for end sequencing and chromosome walking. Here we describe efficient methods for end-DNA isolation. The entire process, including small-scale DNA preparation, restriction digestion, self-ligation, and PCR with vector-based primers, is carried out in 96-well formats. Using a Fosmid library of genomic DNA of Candida albicans, PCR products ranging in size from 0.1 to 8 kbp were generated from 118 end sequences in 140 reactions from 70 Fosmid clones. A single or a prominent band was found in 101 of these reactions. Twenty-six of these bands were tested for walking and all of them proved to be specific. Thus, the system overcomes the disadvantage caused by low copy number. This system allows rapid physical mapping of genomes, and is adaptable for several other vectors including BAC (bacterial artificial chromosome), PAC (P1-derived artificial chromosome), and YAC (yeast artificial chromosome).     

High Throughput BAC DNA Isolation for Physical Map Construction of Sorghum (Sorghum bicolor)

With the aim of constructing a physical map of sorghum, we developed a rapid, high throughput approach for isolating BAC DNA suitable for restriction endonuclease digestion fingerprinting, PCR- based STS-content mapping, and BAC-end sequencing. The system utilizes a programmable 96 channel liquid handling system and associated accessories that permit bacterial cultivation and DNA isolation in 96-well plate format. This protocol details culture conditions that optimize bacterial growth in deep-well plates and criteria for BAC DNA isolation to obtain high yields of quality BAC DNA. The system is robust, accurate, and relatively cost-effective. The BAC DNA isolation system has been tested during efforts to construct a physical map of sorghum.     

High-throughput plasmid mini preparations facilitated by micro-mixing.

We have developed a reliable high-throughput plasmid isolation system using a 96-well plate format. This system combines a novel glass bead micro-mixing method with modified alkaline lysis and Sephacryl S-500 DNA purification procedures. Mechanical forces generated by vortexing glass beads inside each well of the 96-well plates ensure that the bacterial pellets are homogeneously resuspended, the cells are completely lyzed, and the resulting bacterial lysates are thoroughly mixed with the potassium acetate solution. The vortexing speed and duration for glass bead mixing have been standardized to facilitate plasmid DNA yields without significant adjustments.     

A Method for Preparing DNA Sequencing Templates Using a DNA-Binding Microplate

A DNA-binding matrix was immobilized on the surface of a 96-well microplate and used for plasmid DNA preparation for DNA sequencing. The same DNA-binding plate was used for bacterial growth, cell lysis, DNA purification, and storage. In a single step using one buffer, bacterial cells were lysed by enzymes, and released DNA was captured on the plate simultaneously. After two wash steps, DNA was eluted and stored in the same plate. Inclusion of phosphates in the culture medium was found to enhance the yield of plasmid significantly. Purified DNA samples were used successfully in DNA sequencing with high consistency and reproducibility. Eleven vectors and nine libraries were tested using this method. In 10 μl sequencing reactions using 3 μl sample and 0.25 μl BigDye Terminator v3.1, the results from a 3730xl sequencer gave a success rate of 90–95% and read-lengths of 700 bases or more. The method is fully automatable and convenient for manual operation as well. It enables reproducible, high-throughput, rapid production of DNA with purity and yields sufficient for high-quality DNA sequencing at a substantially reduced cost.     

A strategy for recovering high quality genomic DNA from a large number of Phytophthora isolates

We present a strategy to recover high molecular weight genomic DNA from large numbers of isolates of Phytophthora. Included are steps for generating mycelial mass in 24-well reuseable deep well plates, efficient lyophilization and disruption of the mycelium and genomic DNA extraction with 96-well glass fiber filter plates. The resulting DNA is consistently high molecular weight and is suitable for applications that require high quality DNA such as AFLP analysis and TILLING. A single operator easily can manage mycelium preparation and/or DNA extraction from 384 isolates in a single day and this approach might be useful for other fungi or fungi-like organisms that can be grown in liquid media.     

Rapid and Sensitive Detection of Xanthomonas fragariae by Simple Alkaline DNA Extraction and the Polymerase Chain Reaction

Methods for DNA preparation from Xanthomonas fragariae in infected or artificially contaminated strawberry plants were compared in diagnostic assays using the polymerase chain reaction (PCR). The bacterium was detected using PCR with primers specific to a region of its hrp gene. Sensitivity of detection was 1.25 ×l 10³ CFU ml^-1 using DNA from bacterial suspensions prepared by an alkali extraction method. This was 10-fold more sensitive than DNA extraction by boiling, and was equal to that in which DNA was prepared by a more involved cetyltrimethylammonium bromide (CTAB) procedure. Sensitivity of detection from artificially contaminated strawberry tissues was 10-fold less than that from cell suspensions. The results indicated that a rapid and simple method of alkali DNA sample preparation is applicable for the sensitive and reliable detection of X. fragariae and possibly other plant pathogenic bacteria.     

LoPPS: a long PCR product sequencing method for rapid characterisation of long amplicons

Here, we propose an optimised protocol (LoPPS, long PCR product sequencing) which allows the fast, cost-attractive, and high-throughput sequencing of long PCR products. LoPPS constitutes an alternative to the primer-walking technology which is expensive and time consuming but remains the current standard procedure. It is based on the ultrasonic shearing, polishing, and cloning of PCR or RT-PCR products and is compatible with 96- or 384-well microplate systems in which bacterial growth, preparation of plasmid DNA, and sequencing can be automated. We present results obtained from 24 different RT-PCR products (2.5-4.8 kbp long) obtained from various RNA viruses and fully sequenced using LoPPS. The method proved to be robust and fast. It was successfully used on a low amount of DNA and allowed each target nucleotide position to be controlled twice or more, with a final cost which is one-third of that of primer-walking.     

Evaluation of 96-well high-throughput DNA extraction methods for 16S rRNA gene metabarcoding

Gaining meaningful insights into bacterial communities associated with animal hosts requires the provision of high-quality nucleic acids. Although many studies have compared DNA extraction methods for samples with low bacterial biomass (e.g. water) or specific PCR inhibitors (e.g. plants), DNA extraction bias in samples without inherent technical constraint (e.g. animal samples) has received little attention. Furthermore, there is an urgent need to identify a DNA extraction methods in a high-throughput format that decreases the cost and time for processing large numbers of samples. We here evaluated five DNA extraction protocols, using silica membrane-based spin columns and a 96-well microplate format and based on either mechanical or enzymatic lysis or a combination of both, using three bacterial mock communities and Illumina sequencing of the V4 region of the 16SrRNA gene. Our results showed that none of the DNA extraction methods fully eliminated bias associated with unequal lysis efficiencies. However, we identified a DNA extraction method with a lower bias for each mock community standard. Of these methods, those including an enzymatic lysis showed biases specific to some bacteria. Altogether, these results again demonstrate the importance of DNA extraction standardization to be able to compare the microbiome results of different samples. In this attempt, we advise for the use of the 96-well DNeasy Blood and Tissue kit (Qiagen) with a zirconia bead-beating procedure, which optimizes altogether the cost, handling time and bacteria-specific effects associated with enzymatic lysis.     

Generation of transgenic medaka using modified bacterial artificial chromosome

The availability of bacterial artificial chromosome (BAC) offers a good genomic platform for a targeted integration of an exogenous gene by a homologous recombination system in Escherichia coli . In combination with microinjection technology, this system allows for the analysis of various aspects of biological phenomena occurring in vivo using Japanese medaka fish ( Oryzias latipes ). Here we describe a streamlined procedure for selecting BAC clones based on the medaka University of Tokyo genome browser (UTGB), followed by rapid modification with enhanced green fluorescent protein (EGFP) or DsRed fragments for transgenic analysis in medaka. Experimental procedures for BAC DNA preparation, microinjection of medaka embryos and screening of resulting transgenic medaka carrying EGFP/DsRed modified BAC clones are also described.     

Direct sequencing of terminal regions of genomic P1 clones: A general strategy for the design of sequence-tagged site markers

A method for the preparation of P1 DNA is presented, which allows the direct sequencing of ends of inserts in genomic P1 clones using the Applied Biosystems 373A DNA Sequencer and the Dye Terminator sequencing methodology. We surveyed several common methods of DNA preparation including alkaline lysis, Triton-lysozyme lysis, CsCl density-gradient purification, and a commercial column matrix DNA purification kit manufactured by Qiagen. We found that a modified alkaline lysis preparation of P1 DNA was most successful for generating P1 DNA that could be sequenced directly. We also noted that the host bacterial strain from which the P1 DNA was purified dramatically affected the quality of sequencing templates. The bacterial strains NS3145 and NS3529, in which the Drosophila melanogaster and human P1 genomic libraries are harbored, routinely yielded poor-quality sequencing templates. However, the bacterial strain DH10B routinely yielded P1 DNA that was sequenced successfully. A bacterial mating scheme is presented that exploits γδ transposition events to allow the transfer of P1 clones from the library host strain to DH10B. Using either an SP6 or a T7 primer, an average of 350 base pairs of DNA sequence was obtained with an uncalled base frequency of ∼2%. About 4% of P1 end sequences generated corresponded to unique Drosophila loci present in the Genbank database. These single-pass DNA sequences were used to design sequence-tagged site markers for physical mapping studies in both humans and Drosophila.     

Generation of DNA nanocircles containing mismatched bases

The DNA mismatch repair (MMR) system recognizes and repairs errors that escaped the proofreading function of DNA polymerases. To study molecular details of the MMR mechanism, in vitro biochemical assays require specific DNA substrates carrying mismatches and strand discrimination signals. Current approaches used to generate MMR substrates are time-consuming and/or not very flexible with respect to sequence context. Here we report an approach to generate small circular DNA containing a mismatch (nanocircles). Our method is based on the nicking of PCR products resulting in single-stranded 3' overhangs, which form DNA circles after annealing and ligation. Depending on the DNA template, one can generate mismatched circles containing a single hemimethylated GATC site (for use with the bacterial system) and/or nicking sites to generate DNA circles nicked in the top or bottom strand (for assays with the bacterial or eukaryotic MMR system). The size of the circles varied (323 to 1100 bp), their sequence was determined by the template DNA, and purification of the circles was achieved by ExoI/ExoIII digestion and/or gel extraction. The quality of the nanocircles was assessed by scanning-force microscopy and their suitability for in vitro repair initiation was examined using recombinant Escherichia coli MMR proteins.     

Autoclave method for rapid preparation of bacterial PCR-template DNA

An autoclave method for preparing bacterial DNA for PCR template is presented, it eliminates the use of detergents, organic solvents, and mechanical cellular disruption approaches, thereby significantly reducing processing time and costs while increasing reproducibility. Bacteria are lysed by rapid heating and depressurization in an autoclave. The lysate, cleared by microcentrifugation, was either used directly in the PCR reaction, or concentrated by ultrafiltration. This approach was compared with seven established methods of DNA template preparation from four bacterial sources which included boiling Triton X-100 and SDS, bead beating, lysozyme/proteinase K, and CTAB lysis method components. Bacteria examined were Enterococcus and Escherichia coli, a natural marine bacterial community and an Antarctic cyanobacterial-mat. DNAs were tested for their suitability as PCR templates by repetitive element random amplified polymorphic DNA (RAPD) and denaturing gradient gel electrophoresis (DGGE) analysis. The autoclave method produced PCR amplifiable template comparable or superior to the other methods, with greater reproducibility, much shorter processing time, and at a significantly lower cost.     

Detection of enterotoxigenic Clostridium perfringens in meat samples by using molecular methods

To prevent food-borne bacterial diseases and to trace bacterial contamination events to foods, microbial source tracking (MST) methods provide important epidemiological information. To apply molecular methods to MST, it is necessary not only to amplify bacterial cells to detection limit levels but also to prepare DNA with reduced inhibitory compounds and contamination. Isolates carrying the Clostridium perfringens enterotoxin gene (cpe) on the chromosome or a plasmid rank among the most important food-borne pathogens. Previous surveys indicated that cpe-positive C. perfringens isolates are present in only ～5% of nonoutbreak food samples and then only at low numbers, usually less than 3 cells/g. In this study, four molecular assays for the detection of cpe-positive C. perfringens isolates, i.e., ordinary PCR, nested PCR, real-time PCR, and loop-mediated isothermal amplification (LAMP), were developed and evaluated for their reliability using purified DNA. For use in the artificial contamination of meat samples, DNA templates were prepared by three different commercial DNA preparation kits. The four molecular assays always detected cpe when >103 cells/g of cpe-positive C. perfringens were present, using any kit. Of three tested commercial DNA preparation kits, the InstaGene matrix kit appeared to be most suitable for the testing of a large number of samples. By using the InstaGene matrix kit, the four molecular assays efficiently detected cpe using DNA prepared from enrichment culture specimens of meat samples contaminated with low numbers of cpe-positive C. perfringens vegetative cells or spores. Overall, the current study developed molecular assay protocols for MST to detect the contamination of foods with low numbers of cells, and at a low frequency, of cpe-positive C. perfringens isolates.     

Heliomycin suppression of RNA synthesis in a cell-free system]

Heliomycin inhibited in vitro the RNA-polymerase reaction catalyzed by the preparation of DNA-dependent RNA-polymerase from E. coli. The blocking effect increased with a rise in the antibiotic concentration. The inhibitory effect of heliomycin decreased, when the amount of RNA-polymerase in the system increased. Yet, it did not depend on the content of DNA and the nature of the DNA preparation. Preincubation of RNA-polymerase with DNA resulting in formation of the enzyme-matrix complex did not prevent blocking RNA synthesis by heliomycin. Suppression of the RNA-polymerase reaction did not depend on the time of the antibiotic addition to the polymerizing system. Heliomycin had a significant activity not only with respect to the bacterial RNA-polymerase, but also in the system containing the enzyme isolated from the cells of Crithidia oncopelti.     

The immunostimulating effect of bacterial genomic DNA on the innate immune responses of bivalve mussel, Hyriopsis cumingii Lea

The genomic DNA of Escherichia coli, which contains the unmethylated CpG motif, was used to evaluate the immunostimulating effect of bacterial DNA on innate immune responses in the bivalve mussel Hyriopsis cumingii Lea. The results showed that the E. coli DNA had no significant effect on the production of superoxide anion (O(2-)) or acid phosphatase (AP) by haemocytes in vitro. However, the bactericidal activity of the haemocytes was significantly increased when the cells were incubated with 50 or 100mug/ml bacterial DNA for 12 and 24h. Antibacterial activity, lysozyme activity, and prophenoloxidase (proPO) production of haemolymph were also increased, when the bivalve molluscs were injected with 50 or 100mug/ml of bacterial DNA for 12 and 24h. These activities returned to the control level after 48h. This work showed the bacterial DNA with unmethylated CpG motif could activate some parameters of the immune system of bivalve molluscs in vivo and in vitro.     

Magnetic bead purification of M13 DNA sequencing templates.

A method for the preparation of multiple M13 DNA sequencing templates is described. No phenol extraction is required and the procedure can be carried out in Eppendorf tubes or 96-well microtiter plates. Starting with a phage supernatant, the entire procedure is carried out in the same reaction vessel and all separation steps are based on a novel application of magnetic bead separation. The design of a 96-well magnetic separator is presented and the application of the method for large-scale sequencing is discussed.     

A new automated method for isolation of Chlamydia trachomatis from urine eliminates inhibition and increases robustness for NAAT systems

Chlamydia trachomatis is a leading cause of sexually transmitted infection. Diagnostic methods with easy non-invasive sample collection are important to increase testing and hence to reduce the spread of this infection. To enable more use of urine samples in C. trachomatis diagnostics, automation is an absolute requirement since obtaining high-quality DNA from urine specimens involves extensive processing.

Here, we present a study in which a new automated sample preparation method, BUGS'n BEADS™ STI (BnB STI), was used up-front of the BDProbeTec™ ET end point analysis and compared with the full BDProbeTec™ ET method to analyze C. trachomatis in 1002 urine samples.

The BnB STI system represents a new concept within magnetic sample preparation in which bacteria are first isolated from the sample material followed by purification of bacterial nucleic acid using the same magnetic particles. Similar sensitivity and specificity were obtained with both methods. None of the samples processed with BnB STI inhibited the BDProbeTec™ ET test whereas 1.8% showed inhibition when processed according to the manual BDProbeTec™ ET DNA preparation method. Moreover, the average MOTA scores obtained with the BnB STI system were 48% higher for all amplification controls and 57% higher for positive samples, compared to the manual sample preparation. Based on these results and the significant reduction in hands-on-time for urine sample processing, the automated BnB STI sample preparation method was implemented for routine analysis of C. trachomatis from urine samples.     

Effect of double-stranded DNA on maturation of dendritic cells in vitro

A preparation of human genomic fragmented double-stranded DNA (dsDNA) was used as maturation stimulus in cultures of human dendritic cells (DCs) generated in compliance with the interferon protocol. Culturing of the DCs in medium with 5 μg/ml of the DNA preparation was associated with a decrease in the relative proportion of CD14 + cells and an increase in that of CD83 + cells. These changes are markers of DC maturation. The efficiency with which the DNA preparation was able to elicit DC maturation was commensurate with that of lypopolysaccharide from bacterial cell, the standard inducer of DC maturation. Generated ex vivo, matured in the presence of the human DNA preparation, pulsed with tumor antigens mouse DCs were used as a vaccine in biological tests for its antitumor activity. The experimental results demonstrate that reinfusion of mature pulsed with tumor antigens DCs cause a statistically significant suppression of tumor graft growth.