Determining a minimum detection threshold in terminal restriction fragment length polymorphism analysis

Terminal restriction fragment length polymorphism (T-RFLP) analysis is a common technique used to characterize soil microbial diversity. The fidelity of this technique in accurately reporting diversity has not been thoroughly evaluated. Here we determine if rare fungal species can be reliably detected by T-RFLP analysis. Spores from three arbuscular mycorrhizal fungal species were each mixed at a range of concentrations (1%, 10%, 50%, and 100%) with Glomus irregulare to establish a minimum detection threshold. T-RFLP analysis was capable of detecting diagnostic peaks of rare taxa at concentrations as low as 1%. The relative proportion of the target taxa in the sample and DNA concentration influenced peak detection reliability. However, low concentrations produced small, inconsistent electropherogram peaks contributing to difficulty in differentiating true peaks from signal noise. The results of this experiment suggest T-RFLP is a reproducible and high fidelity procedure, which requires careful data interpretation in order to accurately characterize sample diversity.     

Multiplex-terminal restriction fragment length polymorphism

A novel method called "multiplex-terminal restriction fragment length polymorphism (M-TRFLP)" has been recently developed which can be used for simultaneous analysis of the community composition of two or more microbial taxa (up to four). This method can also be used for microbial diagnostic purposes. For M-TRFLP analysis, primers specific to different target genes are used for multiplex-PCR, with one primer for each target being labeled with a unique fluorescent dye at its 5' end. Restriction digestion of the amplified products followed by fragment size analysis on a DNA sequencer produces profiles for targeted genes, which can be distinguished from each other by the color of the terminal fragments imparted by the unique fluorescent dye used for primer labeling. In contrast to current protocols, M-TRFLP allows multiple communities or multiple targets (genes) data to be obtained in just one reaction and therefore saves time, cost and labor. This protocol can be completed in 5-8 h.     

Residual polymerase activity-induced bias in terminal restriction fragment length polymorphism analysis

Residual activity of polymerase chain reaction DNA polymerases in restriction analyses strongly affected genetic profiling based on terminal restriction fragment length polymorphisms. Artificial fragment sizes produced as a result of 5'-overhang restriction site fill-in and addition of a terminal A may bias genetic profiling and genotyping of microbial communities. Efficient removal of polymerases retained original fragment sizes and significantly reduced this profiling bias in soil bacterial communities.     

HLA-DR genotyping by restriction fragment length polymorphism analyses

We have established unique restriction fragment length polymorphism (RFLP) patterns characteristic of homozygous typing cells (HTCs) for HLA-DR-1 through HLA-DR-8 haplotypes. These RFLP patterns were found to segregate in family members and correlate 100% with HLA-DR antibody phenotyping. The RFLP patterns were used to type chronic myelocytic leukemic cells which have a Philadelphia translocation from 23 randomly selected Caucasoid patients. The results show an alternative method for the determination of the HLA-DR types without using live cells and to study disease association with the HLA-DR region.     

Renin locus restriction fragment length polymorphism

Summary The use of two genomic EcoRI fragments as probes is discussed.     

Detection of linkage between restriction fragment length polymorphism markers and quantitative traits

Summary Methodologies commonly used to detect linkage of marker loci to loci affecting quantitative traits are discussed. It is shown that variances for the quantitative trait differ among marker genotypes when using F₂ or pooled backcross data if linkage exists. Hence, to analyze this type of data by single factor ANOVA or other statistical techniques that assume a common variance is inadequate. Restriction fragment length polymorphism (RFLP) markers are a powerful tool in plant breeding but cost is an important drawback; hence, a methodology is suggested to obtain the minimum number of plants in F₂ populations to detect such linkage.     

Assessment of anaerobic wastewater treatment failure using terminal restriction fragment length polymorphism analysis

AIMS: The suitability of genetic fingerprinting to study the microbiological basis of anaerobic bioreactor failure is investigated. METHODS AND RESULTS: Two laboratory-scale anaerobic expanded granular sludge bed bioreactors, R1 and R2, were used for the mesophilic (37 degrees C) treatment of high-strength [10 g chemical oxygen demand (COD) l(-1)] synthetic industrial-like wastewater over a 100-day trial period. A successful start up was achieved by both bioreactors with COD removal over 90%. Both reactors were operated under identical parameters; however, increased organic loading during the trial induced a reduction in the COD removal of R1, while R2 maintained satisfactory performance (COD removal >90%) throughout the experiment. Specific methanogenic activity measurements of biomass from both reactors indicated that the main route of methane production was hydrogenotrophic methanogenesis. Terminal restriction fragment length polymorphism (TRFLP) analysis was applied to the characterization of microbial community dynamics within the system during the trial. The principal differences between the two consortia analysed included an increased abundance of Thiovulum- and Methanococcus-like organisms and uncultured Crenarchaeota in R1. CONCLUSIONS: The results indicated that there was a microbiological basis for the deviation, in terms of operational performance, of R1 and R2. SIGNIFICANCE AND IMPACT OF THE STUDY: High-throughput fingerprinting techniques, such as TRFLP, have been demonstrated as practically relevant for biomonitoring of anaerobic reactor communities.     

T-Align, a web-based tool for comparison of multiple terminal restriction fragment length polymorphism profiles

Terminal restriction fragment length polymorphism (tRFLP) is a potentially high-throughput method for the analysis of complex microbial communities. Comparison of multiple tRFLP profiles to identify shared and unique components of microbial communities however, is done manually, which is both time consuming and error prone. This paper describes a freely accessible web-based program, T-Align (http://inismor.ucd.ie/~talign/), which addresses this problem. Initially replicate profiles are compared and used to generate a single consensus profile containing only terminal restriction fragments that occur in all replicate profiles. Subsequently consensus profiles representing different communities are compared to produce a list showing whether a terminal restriction fragment (TRF) is present in a particular sample and its relative fluorescence intensity. The use of T-Align thus allows rapid comparison of numerous tRFLP profiles. T-Align is demonstrated by alignment of tRFLP profiles generated from bacterioplankton communities collected from the Irish and Celtic Seas in November 2000. Ubiquitous TRFs and site-specific TRFs were identified using T-Align.     

Horizontal heterogeneity of denitrifying bacterial communities in marine sediments by terminal restriction fragment length polymorphism analysis

Although it is widely believed that horizontal patchiness exists in microbial sediment communities, determining the extent of variability or the particular members of the bacterial community which account for the observed differences among sites at various scales has not been routinely demonstrated. In this study, horizontal heterogeneity was examined in time and space for denitrifying bacteria in continental shelf sediments off Tuckerton, N.J., at the Rutgers University Long-Term Ecosystem Observatory (LEO-15). Characterization of the denitrifying community was done using PCR amplification of the nitrous oxide reductase (nosZ) gene combined with terminal restriction fragment length polymorphism analysis. Spatial scales from centimeters to kilometers were examined, while temporal variation was assayed over the course of 1995 to 1996. Sorenson's indices (pairwise similarity values) were calculated to permit comparison between samples. The similarities of benthic denitrifiers ranged from 0.80 to 0.85 for centimeter scale comparisons, from 0.52 to 0.79 for meter level comparisons, and from 0.23 to 0.53 for kilometer scale comparisons. Sorenson's indices for temporal comparisons varied from 0.12 to 0.74. A cluster analysis of the similarity values indicated that the composition of the denitrifier assemblages varied most significantly at the kilometer scale and between seasons at individual stations. Specific nosZ genes were identified which varied at centimeter, meter, or kilometer scales and may be associated with variability in meio- or macrofaunal abundance (centimeter scale), bottom topography (meter scale), or sediment characteristics (kilometer scale).     

Biases for detecting arbuscular mycorrhizal fungal mixture by terminal restriction fragment length polymorphism (T-RFLP)

Terminal restriction fragment length polymorphism (T-RFLP) analysis of amplified ribosomal RNA genes is used for profiling microbial communities and sometimes for species richness and relative abundance estimation in environmental samples. However, the T-RFLP fingerprint may be subject to biases during the procedure, influencing the detection of real community structures in the environment. To investigate possible sources of T-RFLP bias, 18S rRNA gene clones derived from two arbuscular mycorrhizal fungal sequences were combined in simple pairwise mixes to assess the effects of polymerase chain reaction cycle number, plant genomic DNA purification method and varying template ratio on the template-to-product ratio as measured by relative T-RF peak area. Varying cycle numbers indicated that amplification was still in the exponential phase at the cycle numbers lower than 18, so these small cycle numbers were used for the comparison of template-to-product quantities. Relative abundance estimated from T-RF peak ratios varied with different purification procedures, but the best results, closest to input ratios, were obtained by using phenol–chloroform purification. The presence of an excess of unpurified non-target plant genomic DNA generated a bias towards lower or overestimation of relative abundance. We conclude that a low number of amplification cycles and stringent DNA purification are necessary for accurate mixed sample analysis by T-RFLP.     

Terminal restriction fragment length polymorphism data analysis for quantitative comparison of microbial communities

Terminal restriction fragment length polymorphism (T-RFLP) is a culture-independent method of obtaining a genetic fingerprint of the composition of a microbial community. Comparisons of the utility of different methods of (i) including peaks, (ii) computing the difference (or distance) between profiles, and (iii) performing statistical analysis were made by using replicated profiles of eubacterial communities. These samples included soil collected from three regions of the United States, soil fractions derived from three agronomic field treatments, soil samples taken from within one meter of each other in an alfalfa field, and replicate laboratory bioreactors. Cluster analysis by Ward's method and by the unweighted-pair group method using arithmetic averages (UPGMA) were compared. Ward's method was more effective at differentiating major groups within sets of profiles; UPGMA had a slightly reduced error rate in clustering of replicate profiles and was more sensitive to outliers. Most replicate profiles were clustered together when relative peak height or Hellinger-transformed peak height was used, in contrast to raw peak height. Redundancy analysis was more effective than cluster analysis at detecting differences between similar samples. Redundancy analysis using Hellinger distance was more sensitive than that using Euclidean distance between relative peak height profiles. Analysis of Jaccard distance between profiles, which considers only the presence or absence of a terminal restriction fragment, was the most sensitive in redundancy analysis, and was equally sensitive in cluster analysis, if all profiles had cumulative peak heights greater than 10,000 fluorescence units. It is concluded that T-RFLP is a sensitive method of differentiating between microbial communities when the optimal statistical method is used for the situation at hand. It is recommended that hypothesis testing be performed by redundancy analysis of Hellinger-transformed data and that exploratory data analysis be performed by cluster analysis using Ward's method to find natural groups or by UPGMA to identify potential outliers. Analyses can also be based on Jaccard distance if all profiles have cumulative peak heights greater than 10,000 fluorescence units.     

TRFMA: a web-based tool for terminal restriction fragment length polymorphism analysis based on molecular weight

TRFMA provides a Web environment for analyzing T-RFLP results based on molecular weights of the fragments, rather than the numbers of nucleotides, to increase accuracy. The 16S rRNA data are saved as an XML file containing around 650 sequences (light version) and a MySQL database containing around 50 000 sequences (full version), which are connected to Web server via PHP5 and manipulated on an Internet browser. AVAILABILITY: TRFMA is freely available at http://myamagu.dent.kyushu-u.ac.jp/bioinformatics/trfma/index.html and can be downloaded from the same site.     

Monitoring of phytoplankton community structure using terminal restriction fragment length polymorphism (T-RFLP)

To establish molecular monitoring for the phytoplankton community in aquatic ecosystems, we analysed the terminal restriction fragment length polymorphism (T-RFLP) of small subunit ribosomal RNA gene (18S rDNA) sequences of nuclear genomes from the algal strains of culture collections and environmental samples of two freshwater reservoirs (Sangcheon reservoir and Seoho reservoir, Korea). Terminal restriction fragment (T-RF) length database was also constructed from twelve strains of algal culture collections to annotate and identify the phytoplankton species from T-RFLP profiles. Algal species in reservoirs were identified and monitored through the colony sequencing and T-RF length patterns of 18S rRNA. In this study, 41 unique clones were identified from two reservoirs including Chlorophyta, Cryptophyta, and Alveolata. In the case of Cryptomonas sp., we found significant linear relationships between T-RF peak areas and biovolumes by cell counting. Our results suggest that T-RFLP analysis can be a fast and quantitative monitoring tool for species changes in phytoplankton communities.     

Amplified restriction fragment length polymorphism in parasite genetics

The amplified restriction fragment length polymorphism (AFLP) technique is a relatively new method for the analysis of polymorphism that has not yet been widely used in parasitology. In this article, Dan Masiga, Andy Tait and Mike Turner provide a brief introduction to AFLP and illustrate how it can be used in the investigation of marker inheritance in genetic crosses and in the analysis of polymorphism of field populations. They also briefly highlight the strengths and weaknesses of AFLP in comparison with other methods for detecting polymorphism and conclude that AFLP is a very useful addition to the range of techniques available.     

Formation of pseudo-terminal restriction fragments,a PCR-related bias affecting terminal restriction fragment length polymorphism analysis of microbial community structure

Terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified genes is a widely used fingerprinting technique in molecular microbial ecology. In this study, we show that besides expected terminal restriction fragments (T-RFs), additional secondary T-RFs occur in T-RFLP analysis of amplicons from cloned 16S rRNA genes at high frequency. A total of 50% of 109 bacterial and 78% of 68 archaeal clones from the guts of cetoniid beetle larvae, using MspI and AluI as restriction enzymes, respectively, were affected by the presence of these additional T-RFs. These peaks were called "pseudo-T-RFs" since they can be detected as terminal fluorescently labeled fragments in T-RFLP analysis but do not represent the primary terminal restriction site as indicated by sequence data analysis. Pseudo-T-RFs were also identified in T-RFLP profiles of pure culture and environmental DNA extracts. Digestion of amplicons with the single-strand-specific mung bean nuclease prior to T-RFLP analysis completely eliminated pseudo-T-RFs. This clearly indicates that single-stranded amplicons are the reason for the formation of pseudo-T-RFs, most probably because single-stranded restriction sites cannot be cleaved by restriction enzymes. The strong dependence of pseudo-T-RF formation on the number of cycles used in PCR indicates that (partly) single-stranded amplicons can be formed during amplification of 16S rRNA genes. In a model, we explain how transiently formed secondary structures of single-stranded amplicons may render single-stranded amplicons accessible to restriction enzymes. The occurrence of pseudo-T-RFs has consequences for the interpretation of T-RFLP profiles from environmental samples, since pseudo-T-RFs may lead to an overestimation of microbial diversity. Therefore, it is advisable to establish 16S rRNA gene sequence clone libraries in parallel with T-RFLP analysis from the same sample and to check clones for their in vitro digestion T-RF pattern to facilitate the detection of pseudo-T-RFs.     

Using terminal restriction fragment length polymorphism (T-RFLP) to identify mycorrhizal fungi: a methods review

Terminal restriction fragment length polymorphism (T-RFLP) is an increasingly widely used technique in mycorrhizal ecology. In this paper, we review the technique as it is used to identify species of mycorrhizal fungi and distinguish two different versions of the technique: peak-profile T-RFLP (the original version) and database T-RFLP. We define database T-RFLP as the use of T-RFLP to identify individual species within samples by comparison of unknown data with a database of known T-RFLP patterns. This application of T-RFLP avoids some of the pitfalls of peak-profile T-RFLP and allows T-RFLP to be applied to polyphyletic functional groups such as ectomycorrhizal fungi. The identification of species using database T-RFLP is subject to several sources of potential error, including (1) random erroneous matches of peaks to species, (2) shared T-RFLP profiles across species, and (3) multiple T-RFLP profiles within a species. A mathematical approximation of the risk of the first type of error as a function of experimental parameters is discussed. Although potentially less accurate than some other methods such as clone libraries, the high throughput of database T-RFLP permits much greater replication and may, therefore, be preferable for many ecological questions, particularly when combined with other techniques such as cloning.     

Novel endophytic nitrogen-fixing clostridia from the grass Miscanthus sinensis as revealed by terminal restriction fragment length polymorphism analysis

Anaerobic nitrogen-fixing consortia consisting of N2-fixing clostridia and diverse nondiazotrophic bacteria were previously isolated from various gramineous plants (K. Minamisawa, K. Nishioka, T. Miyaki, B. Ye, T. Miyamoto, M. You, A. Saito, M. Saito, W. Barraquio, N. Teaumroong, T. Sein, and T. Tadashi, Appl. Environ. Microbiol. 70:3096-3102, 2004). For this work, clostridial populations and their phylogenetic structures in a stand of the grass Miscanthus sinensis in Japan were assessed by a 16S rRNA gene-targeted terminal restriction fragment length polymorphism (TRFLP) analysis combined with most-probable-number (MPN) counts. PCR primers and restriction enzymes were optimized for analyses of the plant clostridia. Clostridia were detected in strongly surface-sterilized leaves, stems, and roots of the plants at approximately 10(4) to 10(5) cells/g of fresh weight; they made up a large proportion of N2-fixing bacterial populations, as determined by MPN counts associated with an acetylene reduction assay. Phylogenetic grouping by MPN-TRFLP analysis revealed that the clostridial populations belonged to group II of cluster XIVa and groups IV and V of cluster I; this result was supported by a culture-independent TRFLP analysis using direct DNA extraction from plants. When phylogenetic populations from M. sinensis and the soil around the plants were compared, group II clostridia were found to exist exclusively in M. sinensis.     

New threshold and confidence estimates for terminal restriction fragment length polymorphism analysis of complex bacterial communities

Terminal restriction fragment length polymorphism (T-RFLP) analysis has the potential to be useful for comparisons of complex bacterial communities, especially to detect changes in community structure in response to different variables. To do this successfully, systematic variations have to be detected above method-associated noise, by standardizing data sets and assigning confidence estimates to relationships detected. We investigated the use of different standardizing methods in T-RFLP analysis of PCR-amplified 16S rRNA genes to elucidate the similarities between the bacterial communities in 17 soil and sediment samples. We developed a robust method for standardizing data sets that appeared to allow detection of similarities between complex bacterial communities. We term this the variable percentage threshold method. We found that making conclusions about the similarities of complex bacterial communities from T-RFLP profiles generated by a single restriction enzyme (RE) may lead to erroneous conclusions. Instead, the use of multiple REs, each individually, to generate multiple data sets allowed us to determine a confidence estimate for groupings of apparently similar communities and at the same time minimized the effects of RE selection. In conjunction with the variable percentage threshold method, this allowed us to make confident conclusions about the similarities of the complex bacterial communities in the 17 different samples.     

Rapid DNA purification for restriction fragment length polymorphism analysis

This paper describes a method for isolation of DNA from blood samples involving a rapid chemical disintegration of proteins with 8 M urea and with a minimum of exposure to phenol. The DNA is further desalted and purified on Sephadex G-25 prepacked disposable columns. DNA isolated in this way was pure enough to be immediately cleaved by restriction enzymes.