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Horizontal gene transfer in bacterial and archaeal complete genomes.

There is growing evidence that horizontal gene transfer is a potent evolutionary force in prokaryotes, although exactly how potent is not known. We have developed a statistical procedure for predicting whether genes of a complete genome have been acquired by horizontal gene transfer. It is based on the analysis of G+C contents, codon usage, amino acid usage, and gene position. When we applied this procedure to 17 bacterial complete genomes and seven archaeal ones, we found that the percentage of horizontally transferred genes varied from 1.5% to 14.5%. Archaea and nonpathogenic bacteria had the highest percentages and pathogenic bacteria, except for Mycoplasma genitalium, had the lowest. As reported in the literature, we found that informational genes were less likely to be transferred than operational genes. Most of the horizontally transferred genes were only present in one or two lineages. Some of these transferred genes include genes that form part of prophages, pathogenecity islands, transposases, integrases, recombinases, genes present only in one of the two Helicobacter pylori strains, and regions of genes functionally related. All of these findings support the important role of horizontal gene transfer in the molecular evolution of microorganisms and speciation.

Amino Acids↗

Estimating the number of protein folds and families from complete genome data.

Using the data on proteins encoded in complete genomes, combined with a rigorous theory of the sampling process, we estimate the total number of protein folds and families, as well as the number of folds and families in each genome. The total number of folds in globular, water- soluble proteins is estimated at about 1000, with structural information currently available for about one-third of the number. The sequenced genomes of unicellular organisms encode from approximately 25%, for the minimal genomes of the Mycoplasmas, to 70-80% for larger genomes, such as Escherichia coli and yeast, of the total number of folds. The number of protein families with significant sequence conservation was estimated to be between 4000 and 7000, with structures available for about 20% of these.

Conserved Sequence↗

Extensive mosaic structure revealed by the complete genome sequence of uropathogenic Escherichia coli.

We present the complete genome sequence of uropathogenic Escherichia coli, strain CFT073. A three-way genome comparison of the CFT073, enterohemorrhagic E. coli EDL933, and laboratory strain MG1655 reveals that, amazingly, only 39.2% of their combined (nonredundant) set of proteins actually are common to all three strains. The pathogen genomes are as different from each other as each pathogen is from the benign strain. The difference in disease potential between O157:H7 and CFT073 is reflected in the absence of genes for type III secretion system or phage- and plasmid-encoded toxins found in some classes of diarrheagenic E. coli. The CFT073 genome is particularly rich in genes that encode potential fimbrial adhesins, autotransporters, iron-sequestration systems, and phase-switch recombinases. Striking differences exist between the large pathogenicity islands of CFT073 and two other well-studied uropathogenic E. coli strains, J96 and 536. Comparisons indicate that extraintestinal pathogenic E. coli arose independently from multiple clonal lineages. The different E. coli pathotypes have maintained a remarkable synteny of common, vertically evolved genes, whereas many islands interrupting this common backbone have been acquired by different horizontal transfer events in each strain.

Acute Disease↗

Classification of all putative permeases and other membrane plurispanners of the major facilitator superfamily encoded by the complete genome of Saccharomyces cerevisiae.

On the basis of the complete genome sequence of the budding yeast Saccharomyces cerevisiae, a computer-aided analysis was carried out of all members of the major facilitator superfamily (MFS), which typically consists of permeases with 12 transmembrane spans. Analysis of all 5885 predicted open reading frames identified 186 potential MFS proteins. Binary sequence comparison made it possible to cluster 149 of them into 23 families. Putative permease functions could be assigned to 12 families, the largest including sugar, amino acid, and multidrug transport. Phylogenetic clustering of proteins allowed us to predict a possible permease function for a total of 119 proteins. Multiple sequence alignments were made for all families, and evolutionary trees were constructed for families with at least four members. The latter resulted in the identification of 21 subclusters with presumably tightly related permease function. No functional clues were predicted for a total of 41 clustered or unclustered proteins.

Computers↗

Complete genome sequence of Treponema pallidum, the syphilis spirochete.

The complete genome sequence of Treponema pallidum was determined and shown to be 1,138,006 base pairs containing 1041 predicted coding sequences (open reading frames). Systems for DNA replication, transcription, translation, and repair are intact, but catabolic and biosynthetic activities are minimized. The number of identifiable transporters is small, and no phosphoenolpyruvate:phosphotransferase carbohydrate transporters were found. Potential virulence factors include a family of 12 potential membrane proteins and several putative hemolysins. Comparison of the T. pallidum genome sequence with that of another pathogenic spirochete, Borrelia burgdorferi, the agent of Lyme disease, identified unique and common genes and substantiates the considerable diversity observed among pathogenic spirochetes.

Bacterial Proteins↗

The first complete genome sequence of Ammi majus latent virus from the new natural host culantro.

A potyvirus (isolate AMLV-CQ) infecting culantro (Eryngium foetidum L.) imported from Vietnam was identified by RT-PCR. The complete genome sequence of AMLV-CQ was determined to be 9,549 nucleotides in length. It contains a large open reading frame encoding a 3,082-amino-acid putative polyprotein, flanked by 5´ and 3´ untranslated regions (UTRs) of 77 and 226 nt, respectively. AMLV-CQ is closely related to five other completely sequenced potyviruses, sharing 68-69% nucleotide and 69-70% amino acid sequence identity. However, the coat protein (CP) gene shares 89% nucleotide and 93% amino acid sequence identity with that of a partially sequenced potyvirus, Ammi majus latent virus (isolate AMLV-WF17). These results suggest that AMLV-CQ and AMLV-WF17 are isolates of the same species. To our knowledge, this is the first report of a complete genome sequence of an AMLV isolate, and culantro was identified as a new natural host for this virus. In addition, a one-step RT-PCR assay was developed that provides a rapid, robust, and highly sensitive approach for the detection of AMLV.

Eryngium↗

Complete genomes from a xenic Dolichospermum flosaquae FBCC-A233 culture reveal genome-inferred metabolic asymmetry with associated bacteria.

Cyanobacteria form phycosphere communities with associated bacteria, but genome-resolved resources are needed to formulate testable hypotheses about their metabolic interactions. Here, we reconstructed three complete circular genomes from a unialgal xenic culture, including Dolichospermum flosaquae FBCC-A233 and two associated alphaproteobacterial genomes assigned to Sphingorhabdus sp. and Brevundimonas sp. Genome-wide read mapping and genome-quality assessment supported the three recovered genomes as high-quality circular reconstructions. Comparative genome analysis placed the cyanobacterial genome within the Dolichospermum flosaquae species cluster under the GTDB framework, while the associated bacterial genomes represented Sphingorhabdus sp. and a putative undescribed Brevundimonas species-level lineage. Genome architecture analysis indicated reduced genome size and gene content in Brevundimonas relative to genus-level references although additional metrics did not support a strong conclusion of classical genome streamlining. Selected KEGG module and KO-level reconstructions indicated genome-inferred metabolic asymmetries across the consortium. FBCC-A233 encoded photosynthesis- and nitrogen-related modules and a BioU-mediated de novo biotin biosynthesis route, whereas the associated bacteria lacked complete de novo biotin biosynthesis but retained biotin-dependent carboxylase genes. FBCC-A233 also encoded extensive anaerobic corrinoid biosynthesis potential; however, canonical DMB-containing cobalamin completion, cobamide identity, and complete transporter systems were not resolved. Together, these complete genomes provide a genome-resolved resource for investigating genome-inferred metabolic differentiation and ecological interactions in cyanobacteria-associated bacterial consortia.IMPORTANCEPhycosphere interactions between cyanobacteria and associated bacteria can shape aquatic microbial communities, but many proposed interactions remain difficult to evaluate without genome-resolved resources. This study provides three complete circular genomes from a unialgal xenic Dolichospermum flosaquae culture, capturing the cyanobacterium and two co-maintained bacterial associates. Our analysis identifies genome-inferred metabolic asymmetries, particularly in biotin- and cobamide-related pathways. D. flosaquae FBCC-A233 encoded candidate de novo biotin and corrinoid biosynthesis capacity, whereas the associated bacteria lacked complete de novo pathways but retained cofactor-dependent enzymes. These findings nominate cofactor-related dependencies as experimentally testable hypotheses while emphasizing unresolved uptake, export, cobamide identity, and growth-dependence mechanisms. The complete genomes and KO-level reconstructions generated here provide a resource for future studies of cyanobacteria-associated consortia.

Genome, Bacterial↗

The coding-complete genome sequence of Arabidopsis latent virus 1 from Iraq.

Here, we report the coding-complete genome sequence of Arabidopsis latent virus 1 (ArLV1; Comovirus arabidopsis) from Iraq. The virus was identified by metatranscriptomic sequencing of asymptomatic cucumber (Cucumis sativus) leaves harboring thrips collected from commercial greenhouses. The bipartite genome comprises RNA1 (5,553 nt) and RNA2 (3,582 nt).

Arabidopsis latent virus 1↗

Complete genome sequence of Acinetobacter bacterium strain BZX-2 isolated from hybrid sturgeon.

We report the complete genome sequence of Acinetobacter sp. strain BZX-2, isolated from a hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂). The genome consists of a 3,819,278-bp chromosome with 3,566 predicted protein-coding genes. The genomic characteristics and antibiotic resistance genes identified provide a basis for the prevention and control of sturgeon diseases.

Acinetobacter↗

Complete genomic sequence of human coronavirus OC43: molecular clock analysis suggests a relatively recent zoonotic coronavirus transmission event.

Coronaviruses are enveloped, positive-stranded RNA viruses with a genome of approximately 30 kb. Based on genetic similarities, coronaviruses are classified into three groups. Two group 2 coronaviruses, human coronavirus OC43 (HCoV-OC43) and bovine coronavirus (BCoV), show remarkable antigenic and genetic similarities. In this study, we report the first complete genome sequence (30,738 nucleotides) of the prototype HCoV-OC43 strain (ATCC VR759). Complete genome and open reading frame (ORF) analyses were performed in comparison to the BCoV genome. In the region between the spike and membrane protein genes, a 290-nucleotide deletion is present, corresponding to the absence of BCoV ORFs ns4.9 and ns4.8. Nucleotide and amino acid similarity percentages were determined for the major HCoV-OC43 ORFs and for those of other group 2 coronaviruses. The highest degree of similarity is demonstrated between HCoV-OC43 and BCoV in all ORFs with the exception of the E gene. Molecular clock analysis of the spike gene sequences of BCoV and HCoV-OC43 suggests a relatively recent zoonotic transmission event and dates their most recent common ancestor to around 1890. An evolutionary rate in the order of 4 x 10(-4) nucleotide changes per site per year was estimated. This is the first animal-human zoonotic pair of coronaviruses that can be analyzed in order to gain insights into the processes of adaptation of a nonhuman coronavirus to a human host, which is important for understanding the interspecies transmission events that led to the origin of the severe acute respiratory syndrome outbreak.

Animals↗

HGT-DB: a database of putative horizontally transferred genes in prokaryotic complete genomes.

The Horizontal Gene Transfer DataBase (HGT-DB) is a genomic database that includes statistical parameters such as G+C content, codon and amino-acid usage, as well as information about which genes deviate in these parameters for prokaryotic complete genomes. Under the hypothesis that genes from distantly related species have different nucleotide compositions, these deviated genes may have been acquired by horizontal gene transfer. The current version of the database contains 88 bacterial and archaeal complete genomes, including multiple chromosomes and strains. For each genome, the database provides statistical parameters for all the genes, as well as averages and standard deviations of G+C content, codon usage, relative synonymous codon usage and amino-acid content. It also provides information about correspondence analyses of the codon usage, plus lists of extraneous group of genes in terms of G+C content and lists of putatively acquired genes. With this information, researchers can explore the G+C content and codon usage of a gene when they find incongruities in sequence-based phylogenetic trees. A search engine that allows searches for gene names or keywords for a specific organism is also available. HGT-DB is freely accessible at http://www.fut.es/~debb/HGT.

Amino Acids↗

Complete genome sequences of three effective nitrogen-fixing strains of Bradyrhizobium ottawaense from Canada.

We report complete genome sequences of three nitrogen-fixing Bradyrhizobium ottawaense strains isolated from soybeans in Canada. Each ~9.0 Mb genome (chromosome and plasmid) harbors predicted genes for nodulation, nitrogen fixation, N2O mitigation, phosphate solubilization, iron acquisition, phytohormone production, and stress tolerance, highlighting their potential for sustainable agriculture.

Bradyrhizobium ottawaense↗

How representative are the known structures of the proteins in a complete genome? A comprehensive structural census.

BACKGROUND: Determining how representative the known structures are of the proteins encoded by a complete genome is important for assessing to what extent our current picture of protein stability and folding is overly influenced by biases in the structure databank (PDB). It is also important for improving database-based methods of structure prediction and genome annotation. RESULTS: The known structures are compared to the proteins encoded by eight complete microbial genomes in terms of simple statistics such as sequence length, composition and secondary structure. The known structures are represented by a collection of nonhomologous domains from the PDB and a smaller list of 'biophysical proteins' on which folding experiments have concentrated. The proteins encoded by the genomes are considered as a whole and divided into various regions, such as known-structure homologue, low complexity (nonglobular), transmembrane or linker. Various tests are performed to assess the significance of the reported differences, in both a practical and a statistical sense. CONCLUSIONS: The proteins encoded by the genomes are significantly different from those in the PDB. Their sequence lengths, which follow an extreme value distribution, are longer than the PDB proteins and much longer than the biophysical proteins. Their composition differs from the PDB proteins in having more Lys, Ile, Asn and Gln and less Cys and Trp. This is true overall and especially for the regions corresponding to soluble proteins of as yet unknown fold. Secondary-structure prediction on these uncharacterized regions indicates that they contain on average more helical structure than the PDB; differences about this mean are small, with yeast having slightly more sheet structure and Haemophilus influenzae and Helicobacter pylori more helical structure. Further information is available through the GeneCensus system at http://bioinfo.mbb.yale.edu/genome.

Animals↗

Identification and distribution of protein families in 120 completed genomes using Gene3D.

Using a new protocol, PFscape, we undertake a systematic identification of protein families and domain architectures in 120 complete genomes. PFscape clusters sequences into protein families using a Markov clustering algorithm (Enright et al., Nucleic Acids Res 2002;30:1575-1584) followed by complete linkage clustering according to sequence identity. Within each protein family, domains are recognized using a library of hidden Markov models comprising CATH structural and Pfam functional domains. Domain architectures are then determined using DomainFinder (Pearl et al., Protein Sci 2002;11:233-244) and the protein family and domain architecture data are amalgamated in the Gene3D database (Buchan et al., Genome Res 2002;12:503-514). Using Gene3D, we have investigated protein sequence space, the extent of structural annotation, and the distribution of different domain architectures in completed genomes from all kingdoms of life. As with earlier studies by other researchers, the distribution of domain families shows power-law behavior such that the largest 2,000 domain families can be mapped to approximately 70% of nonsingleton genome sequences; the remaining sequences are assigned to much smaller families. While approximately 50% of domain annotations within a genome are assigned to 219 universal domain families, a much smaller proportion (< 10%) of protein sequences are assigned to universal protein families. This supports the mosaic theory of evolution whereby domain duplication followed by domain shuffling gives rise to novel domain architectures that can expand the protein functional repertoire of an organism. Functional data (e.g. COG/KEGG/GO) integrated within Gene3D result in a comprehensive resource that is currently being used in structure genomics initiatives and can be accessed via http://www.biochem.ucl.ac.uk/bsm/cath/Gene3D/.

Amino Acid Sequence↗

The complete genome and proteome of Mycoplasma mobile.

Although often considered "minimal" organisms, mycoplasmas show a wide range of diversity with respect to host environment, phenotypic traits, and pathogenicity. Here we report the complete genomic sequence and proteogenomic map for the piscine mycoplasma Mycoplasma mobile, noted for its robust gliding motility. For the first time, proteomic data are used in the primary annotation of a new genome, providing validation of expression for many of the predicted proteins. Several novel features were discovered including a long repeating unit of DNA of approximately 2435 bp present in five complete copies that are shown to code for nearly identical yet uniquely expressed proteins. M. mobile has among the lowest DNA GC contents (24.9%) and most reduced set of tRNAs of any organism yet reported (28). Numerous instances of tandem duplication as well as lateral gene transfer are evident in the genome. The multiple available complete genome sequences for other motile and immotile mycoplasmas enabled us to use comparative genomic and phylogenetic methods to suggest several candidate genes that might be involved in motility. The results of these analyses leave open the possibility that gliding motility might have arisen independently more than once in the mycoplasma lineage.

Amino Acid Sequence↗

Multifractal and correlation analyses of protein sequences from complete genomes.

A measure representation of protein sequences similar to the measure representation of DNA sequences proposed in our previous paper [Yu et al., Phys. Rev. E 64, 031903 (2001)] and another induced measure are introduced. Multifractal analysis is then performed on these two kinds of measures of a large number of protein sequences derived from corresponding complete genomes. From the values of the D(q) (generalized dimensions) spectra and related C(q) (analogous specific heat) curves, it is concluded that these protein sequences are not completely random sequences. For substrings with length K=5, the D(q) spectra of all organisms studied are multifractal-like and sufficiently smooth for the C(q) curves to be meaningful. The C(q) curves of all bacteria resemble a classical phase transition at a critical point. But the "analogous" phase transitions of higher organisms studied exhibit the shape of double-peaked specific heat function. But for the classification problem, the multifractal property is not sufficient. When the measure representations of protein sequences from complete genomes are considered as time series, a method based on correlation analysis after removing some memory from the time series is proposed to construct a phylogenetic tree. This construction is shown to be reasonably satisfactory.

Animals↗