Assessment of transfer methods for comparative genomics of regulatory networks in Bacteria

Background: Comparative genomics can leverage the vast amount of available genomic sequences to reconstruct and analyze transcriptional regulatory networks in Bacteria, but the efficacy of this approach hinges on the ability to transfer regulatory network information from reference species to the genomes under analysis. Several methods have been proposed to transfer regulatory information between bacterial species, but the paucity and distributed nature of experimental information on bacterial transcriptional networks have prevented their systematic evaluation. Results: We report the compilation of a large catalog of transcription factor-binding sites across Bacteria and its use to systematically benchmark proposed transfer methods across pairs of bacterial species. We evaluate motif- and accuracy-based metrics to assess the results of regulatory network transfer and we identify the precision-recall area-under-the-curve as the best metric for this purpose due to the large class-imbalanced nature of the problem. Methods assuming conservation of the transcription factor-binding motif (motif-based) are shown to substantially outperform those assuming conservation of regulon composition (network-based), even though their efficiency can decrease sharply with increasing phylogenetic distance. Variations of the basic motif-based transfer method do not yield significant improvements in transfer accuracy. Our results indicate that detection of a large enough number of regulated orthologs is critical for network-based transfer methods, but that relaxing orthology requirements does not improve results. Using the transcriptional regulators LexA and Fur as case examples, we also show how DNA-binding domain sequence similarity can yield confounding results as an indicator of transfer efficiency for motif-based methods. Conclusions: Counter to standard practice, our evaluation of metrics to assess the efficiency of methods for regulatory network information transfer reveals that the area under precision-recall (PR) curves is a more precise and informative metric than that of receiver-operating-characteristic (ROC) curves, confirming similar findings in other class-imbalanced settings. Our systematic assessment of transfer methods reveals that simple approaches to both motif- and network-based transfer of regulatory information provide equal or better results than more elaborate methods. We also show that there are not effective predictors of transfer efficacy, substantiating the long-standing practice of manual curation in comparative genomics analyses

Dispersal and regulation of an adaptive mutagenesis cassette in the bacteria domain

Recently, a multiple gene cassette with mutagenic translation synthesis activity was identified and shown to be under LexA regulation in several proteobacteria species. In this work, we have traced down instances of this multiple gene cassette across the bacteria domain. Phylogenetic analyses show that this cassette has undergone several reorganizations since its inception in the actinobacteria, and that it has dispersed across the bacterial domain through a combination of vertical inheritance, lateral gene transfer and duplication. In addition, our analyses show that LexA regulation of this multiple gene cassette is persistent in all the phyla in which it has been detected, and suggest that this regulation is prompted by the combined activity of two of its constituent genes: a polymerase V homolog and an alpha subunit of the DNA polymerase III

High-speed polymerase chain reaction in CMOS-compatible chips

Consultable des del TDXTítol obtingut de la portada digitalitzadaEn la última década del siglo XX, el campo de los microsistemas para análisis total (µ-TAS) y, más concretamente, el de los DNA-chips ha adquirido una importancia preponderante en el ámbito de los microsistemas. En gran parte, el creciente interés por estos dispositivos se debe a las substanciales mejoras que prometen: análisis más rápidos, baratos y automatizados, pero también es debido a la posibilidad de implementar técnicas analíticas antes impensables (e.g. chips de hibridación). En el caso particular de los DNA-chips, se han desarrollado prototipos funcionales para PCR, LCR, electroforesis en gel, di-electroforesis, hibridación y varias combinaciones de estas técnicas, al tiempo que los chips de hibridación masiva (mayoritariamente basados en arrayers) han llegado a convertirse en un éxito comercial. Aun así, y aunque se ha llevado a cabo mucho trabajo en estos años, es necesaria todavía mucha investigación para afrontar algunos de los principales retos de los DNA-chips. En el transcurso de esta tesis doctoral, se ha llevado a cabo el desarrollo un proceso tecnológico común para la fabricación de DNA-chips multifunción (i.e. sistemas versátiles basados en PCR y electroforesis), poniendo un especial énfasis en la compatibilidad con los procesos CMOS estándar, a fin de conseguir desarrollar prototipos proto-industriales. Como demostrador de esta puesta a punto tecnológica, se han diseñado, fabricado y testado chips de PCR, y la PCR en chips ha sido optimizada con respecto a materiales de fabricación, metodologías de inserción/extracción, composición bioquímica de la mix de PCR, diferentes configuraciones de calentadores/sensores (Peltier/termopares vs. resistencias integradas) y la cinética de la reacción.In the last decade of the twentieth century, the fields of µ-TAS and, more specifically, DNA-chips have acquired increasing importance in the microsystems arena. The main reason for this surge of interest lies in the advantages these new devices seek to bring forth: faster, cheaper and completely automated analyses, and also in the outbreak of novel analytical techniques (e.g. hybridization chips). In the particular case of DNA-chips, functional prototypes have been demonstrated for PCR, LCR, gel electrophoresis, di-electrophoresis, hybridization and various combinations of these techniques, whilst hybridization chips (mainly arrayer chips) have become a successful market application. But, even though a considerable amount of work has been carried out in these few years, much research is still required to address fundamental problems of DNA-chips. In this doctoral work, a common-ground technological setup for the production of multifunction DNA-chips (i.e. PCR plus electrophoresis systems) has been laid down, placing strong emphasis in its compatibility with standard CMOS processes in order to produce proto-industrial prototypes. As a demonstrator of this technological setup, PCR-chips have been designed, manufactured and tested, and the chip PCR reaction has been optimized with respect to surface materials, insertion and extraction methods, biochemical mix composition, heater/sensor setups (Peltier/thermocouple vs. thin-film driven systems) and reaction kinetics

Biochemical analysis and optimization of inhibition and adsorption phenomena in glass-silicon PCR-chips

Altres ajuts: this work was partly funded by the Consejo de Investigaciones Cientı́ficas (CSIC), by Grant TIC97-0569 from the Comisión Interministerial de Ciencia y Tecnologı́a (CICYT)The use of glass-silicon chips for PCR analysis has been widely reported in the last decade, but there have been few systematic efforts to pin down the biochemical problems such systems bring forth. Here we report a systematic analysis of material-related inhibition and adsorption phenomena in glass-silicon PCR-chips. The results suggest that the previously reported inhibition of PCR by silicon-related materials stems mainly from the adsorption of Taq polymerase at chip walls due to increased surface-to-volume ratios, and not from a straight chemical action of silicon-related materials on the PCR-mix. In contrast to Taq polymerase, DNA is not adsorbed in noticeable amounts. The net effect of polymerase adsorption can be counteracted by the addition of a titrated amount of competing protein bovine serum albumin (BSA) and the ensuing reactions can be kinetically optimized in chips to yield effective amplifications in the whereabouts of 20 mi

Aeons of distress : an evolutionary perspective on the bacterial SOS response

The SOS response of bacteria is a global regulatory network targeted at addressing DNA damage. Governed by the products of the lexA and recA genes, it co-ordinates a comprehensive response against DNA lesions and its description in Escherichia coli has stood for years as a textbook paradigm of stress-response systems in bacteria. In this paper we review the current state of research on the SOS response outside E. coli. By retracing research on the identification of multiple diverging LexA-binding motifs across the Bacteria Domain, we show how this work has led to the description of a minimum regulon core, but also of a heterogeneous collection of SOS regulatory networks that challenges many tenets of the E. coli model. We also review recent attempts at reconstructing the evolutionary history of the SOS network that have cast new light on the SOS response. Exploiting the newly gained knowledge on LexA-binding motifs and the tight association of LexA with a recently described mutagenesis cassette, these works put forward likely evolutionary scenarios for the SOS response, and we discuss their relevance on the ultimate nature of this stress-response system and the evolutionary pressures driving its evolutio

In silico analysis reveals substantial variability in the gene contents of the Gammaproteobacteria LexA-regulon

Motivation: Motif-prediction algorithm capabilities for the analysis of bacterial regulatory networks and the prediction of new regulatory sites can be greatly enhanced by the use of comparative genomics approaches. In this study, we make use of a consensus-building algorithm and comparative genomics to conduct an in-depth analysis of the LexA-regulon of gamma proteobacteria, and we use the inferred results to study the evolution of this regulatory network and to examine the usefulness of the control sequences and gene contents of regulons in phylogenetic analysis. - Results: We show, for the first time, the substantial heterogeneity that the LexA-regulon of gamma proteobacteria displays in terms of gene content and we analyze possible branching points in its evolution. We also demonstrate the feasibility of using regulon-related information to derive sound phylogenetic inferences. - Availability: Complementary analysis data and both the source code and the Windows-executable files of the consensus-building software are available at http://www.cnm.es/~ivan/RCGScanner

Origin of the mobile di-hydro-pteroate synthase gene determining sulfonamide resistance in clinical isolates

Sulfonamides are synthetic chemotherapeutic agents that work as competitive inhibitors of the di-hydro-pteroate synthase (DHPS) enzyme, encoded by the folP gene. Resistance to sulfonamides is widespread in the clinical setting and predominantly mediated by plasmid- and integron-borne sul1-3 genes encoding mutant DHPS enzymes that do not bind sulfonamides. In spite of their clinical importance, the genetic origin of sul1-3 genes remains unknown. Here we analyze sul genes and their genetic neighborhoods to uncover sul signature elements that enable the elucidation of their genetic origin. We identify a protein sequence Sul motif associated with sul-encoded proteins, as well as consistent association of a phosphoglucosamine mutase gene (glmM) with the sul2 gene. We identify chromosomal folP genes bearing these genetic markers in two bacterial families: the Rhodobiaceae and the Leptospiraceae. Bayesian phylogenetic inference of FolP/Sul and GlmM protein sequences clearly establishes that sul1-2 and sul3 genes originated as a mobilization of folP genes present in, respectively, the Rhodobiaceae and the Leptospiraceae, and indicate that the Rhodobiaceae folP gene was transferred from the Leptospiraceae. Analysis of %GC content in folP/sul gene sequences supports the phylogenetic inference results and indicates that the emergence of the Sul motif in chromosomally encoded FolP proteins is ancient and considerably predates the clinical introduction of sulfonamides. In vitro assays reveal that both the Rhodobiaceae and the Leptospiraceae, but not other related chromosomally encoded FolP proteins confer resistance in a sulfonamide-sensitive Escherichia coli background, indicating that the Sul motif is associated with sulfonamide resistance. Given the absence of any known natural sulfonamides targeting DHPS, these results provide a novel perspective on the emergence of resistance to synthetic chemotherapeutic agents, whereby preexisting resistant variants in the vast bacterial pangenome may be rapidly selected for and disseminated upon the clinical introduction of novel chemotherapeuticals

Analysis of the SOS response of Vibrio and other bacteria with multiple chromosomes

Background: The SOS response is a well-known regulatory network present in most bacteria and aimed at addressing DNA damage. It has also been linked extensively to stress-induced mutagenesis, virulence and the emergence and dissemination of antibiotic resistance determinants. Recently, the SOS response has been shown to regulate the activity of integrases in the chromosomal superintegrons of the Vibrionaceae, which encompasses a wide range of pathogenic species harboring multiple chromosomes. Here we combine in silico and in vitro techniques to perform a comparative genomics analysis of the SOS regulon in the Vibrionaceae, and we extend the methodology to map this transcriptional network in other bacterial species harboring multiple chromosomes. Results: Our analysis provides the first comprehensive description of the SOS response in a family (Vibrionaceae) that includes major human pathogens. It also identifies several previously unreported members of the SOS transcriptional network, including two proteins of unknown function. The analysis of the SOS response in other bacterial species with multiple chromosomes uncovers additional regulon members and reveals that there is a conserved core of SOS genes, and that specialized additions to this basic network take place in different phylogenetic groups. Our results also indicate that across all groups the main elements of the SOS response are always found in the large chromosome, whereas specialized additions are found in the smaller chromosomes and plasmids. Conclusions: Our findings confirm that the SOS response of the Vibrionaceae is strongly linked with pathogenicity and dissemination of antibiotic resistance, and suggest that the characterization of the newly identified member

Flexible comparative genomics of prokaryotic transcriptional regulatory networks

Comparative genomics methods enable the reconstruction of bacterial regulatory networks using available experimental data. In spite of their potential for accelerating research into the composition and evolution of bacterial regulons, few comparative genomics suites have been developed for the automated analysis of these regulatory systems. Available solutions typically rely on precomputed databases for operon and ortholog predictions, limiting the scope of analyses to processed complete genomes, and several key issues such as the transfer of experimental information or the integration of regulatory information in a probabilistic setting remain largely unaddressed. Here we introduce CGB, a flexible platform for comparative genomics of prokaryotic regulons. CGB has few external dependencies and enables fully customized analyses of newly available genome data. The platform automates the merging of experimental information and uses a gene-centered, Bayesian framework to generate and integrate easily interpretable results. We demonstrate its flexibility and power by analyzing the evolution of type III secretion system regulation in pathogenic Proteobacteria and by characterizing the SOS regulon of a new bacterial phylum, the Balneolaeota. Our results demonstrate the applicability of the CGB pipeline in multiple settings. CGB's ability to automatically integrate experimental information from multiple sources and use complete and draft genomic data, coupled with its non-reliance on precomputed databases and its easily interpretable display of gene-centered posterior probabilities of regulation provide users with an unprecedented level of flexibility in launching comparative genomics analyses of prokaryotic transcriptional regulatory networks. The analyses of type III secretion and SOS response regulatory networks illustrate instances of convergent and divergent evolution of these regulatory systems, showcasing the power of formal ancestral state reconstruction at inferring the evolutionary history of regulatory networks