Effect of mupirocin for Staphylococcus aureus decolonization on the microbiome of the nose and throat in community and nursing home dwelling adults.

OBJECTIVE: To characterize the microbial communities of the anterior nares (nose) and posterior pharynx (throat) of adults dwelling in the community and in nursing homes before and after treatment with intranasal mupirocin. METHODS: Staphylococcus aureus-colonized adults were recruited from the community (n = 25) and from nursing homes (n = 7). S. aureus colonization was confirmed using cultures. Participants had specimens taken from nose and throat for S. aureus quantitation using quantitative PCR for the nuc gene and bacterial profiling using 16S rRNA gene sequencing over 12 weeks. After two baseline study visits 4 weeks apart, participants received intranasal mupirocin for 5 days with 3 further visits over a 8 week follow-up period. RESULTS: We found a decrease in the absolute abundance of S. aureus in the nose for 8 weeks after mupirocin (1693 vs 141 fg/ul, p = 0.047). Mupirocin caused a statistically significant disruption in bacterial communities of the nose and throat after 1 week, which was no longer detected after 8 weeks. Bacterial community profiling demonstrated that there was a decrease in the relative abundance of S. aureus (8% vs 0.3%, p<0.01) 8 weeks after mupirocin and a transient decrease in the relative abundance of Staphylococcus epidermidis in the nose (21% vs 5%, p<0.01) 1 week after mupirocin. CONCLUSIONS: Decolonization with mupirocin leads to a sustained effect on absolute and relative abundance of S. aureus but not for other bacteria in the nose. This demonstrates that a short course of mupirocin selectively decreases S. aureus in the nose for up to 8 weeks.

Comparison of the Microbiota of Older Adults Living in Nursing Homes and the Community.

Our objective for this study was to characterize the microbial communities of the anterior nares (nose), posterior pharynx (throat), and skin of the femoral and subclavian areas in older adults from nursing homes and the community. Older adults (≥65 years) without antibiotic use for the past 3 months were recruited from nursing homes (NH; n = 16) and from the community (CB; n = 51). Specimens were taken from nose, throat, and skin sites for culture and bacterial profiling using 16S rRNA gene sequencing. We found that pathogenic Gram-negative rod (GNR) colonization on the femoral skin was higher in NH participants than CB participants; otherwise, there were no differences in GNR colonization at other body sites or in Staphylococcus aureus colonization at any body site. Bacterial community profiling demonstrated that the operational taxonomic unit compositions of the different body sites were similar between NH and CB participants, but the analysis identified differences in relative abundance levels. Streptococcus spp. were more abundant and Prevotella spp. were less abundant in the throats of NH participants than in throats of CB participants. Proteus, Escherichia coli, and Enterococcus were more abundant in NH participants on the femoral skin. We found a pattern of decreased abundance of specific Proteobacteria in NH participants at the anterior nares and at both skin sites. We concluded that bacterial communities were largely similar in diversity and composition within body sites between older adults without recent antibiotic use from NH compared to those from the community. Our findings support the rationale for improved hygiene in NH residents to reduce the transmission risk of antibiotic-resistant bacteria, such as Enterococcus spp. or Enterobacteriaceae. IMPORTANCE The nose, throat, and skin over the subclavian and femoral veins are the body sites which harbor the bacteria which most commonly cause health care-associated infection. We assessed the effect of nursing home residence on the microbiota of these body sites in older adults. We found that the microbiota composition of the different body sites was similar between nursing home and community participants, but we identified differences in relative abundance levels. We found remarkable similarities in the bacterial communities of different body sites in older adults who lived in nursing homes compared to those in the community among people who had not been on antibiotics for the past 3 months. We also found that the femoral skin microbiota had evidence of stool contamination in the nursing home residents, providing a rationale for improved skin hygiene. Taken together, it appears that the health care environment does not alter the microbiota to the extent that antibiotics do.

Complete genome sequences of Mycoplasma leachii strain PG50T and the pathogenic Mycoplasma mycoides subsp. mycoides small colony biotype strain Gladysdale.

Mycoplasma mycoides subsp. mycoides small colony biotype (SC) is the high-consequence animal pathogen causing contagious bovine pleuropneumonia. We report the complete genome sequences of the pathogenic strain M. mycoides subsp. mycoides SC Gladysdale and a close phylogenetic relative, Mycoplasma leachii PG50(T), another bovine pathogen of the M. mycoides phylogenetic clade.

Genome sequence of the deltaproteobacterial strain NaphS2 and analysis of differential gene expression during anaerobic growth on naphthalene.

BACKGROUND: Anaerobic polycyclic hydrocarbon (PAH) degradation coupled to sulfate reduction may be an important mechanism for in situ remediation of contaminated sediments. Steps involved in the anaerobic degradation of 2-methylnaphthalene have been described in the sulfate reducing strains NaphS3, NaphS6 and N47. Evidence from N47 suggests that naphthalene degradation involves 2-methylnaphthalene as an intermediate, whereas evidence in NaphS2, NaphS3 and NaphS6 suggests a mechanism for naphthalene degradation that does not involve 2-methylnaphthalene. To further characterize pathways involved in naphthalene degradation in NaphS2, the draft genome was sequenced, and gene and protein expression examined. RESULTS: Draft genome sequencing, gene expression analysis, and proteomic analysis revealed that NaphS2 degrades naphthoyl-CoA in a manner analogous to benzoyl-CoA degradation. Genes including the previously characterized NmsA, thought to encode an enzyme necessary for 2-methylnaphthalene metabolism, were not upregulated during growth of NaphS2 on naphthalene, nor were the corresponding protein products. NaphS2 may possess a non-classical dearomatizing enzyme for benzoate degradation, similar to one previously characterized in Geobacter metallireducens. Identification of genes involved in toluene degradation in NaphS2 led us to determine that NaphS2 degrades toluene, a previously unreported capacity. The genome sequence also suggests that NaphS2 may degrade other monoaromatic compounds. CONCLUSION: This study demonstrates that steps leading to the degradation of 2-naphthoyl-CoA are conserved between NaphS2 and N47, however while NaphS2 possesses the capacity to degrade 2-methylnaphthalene, naphthalene degradation likely does not proceed via 2-methylnaphthalene. Instead, carboxylation or another form of activation may serve as the first step in naphthalene degradation. Degradation of toluene and 2-methylnaphthalene, and the presence of at least one bss-like and bbs-like gene cluster in this organism, suggests that NaphS2 degrades both compounds via parallel mechanisms. Elucidation of the key genes necessary for anaerobic naphthalene degradation may provide the ability to track naphthalene degradation through in situ transcript monitoring.

Genome-scale comparison and constraint-based metabolic reconstruction of the facultative anaerobic Fe(III)-reducer Rhodoferax ferrireducens.

BACKGROUND: Rhodoferax ferrireducens is a metabolically versatile, Fe(III)-reducing, subsurface microorganism that is likely to play an important role in the carbon and metal cycles in the subsurface. It also has the unique ability to convert sugars to electricity, oxidizing the sugars to carbon dioxide with quantitative electron transfer to graphite electrodes in microbial fuel cells. In order to expand our limited knowledge about R. ferrireducens, the complete genome sequence of this organism was further annotated and then the physiology of R. ferrireducens was investigated with a constraint-based, genome-scale in silico metabolic model and laboratory studies. RESULTS: The iterative modeling and experimental approach unveiled exciting, previously unknown physiological features, including an expanded range of substrates that support growth, such as cellobiose and citrate, and provided additional insights into important features such as the stoichiometry of the electron transport chain and the ability to grow via fumarate dismutation. Further analysis explained why R. ferrireducens is unable to grow via photosynthesis or fermentation of sugars like other members of this genus and uncovered novel genes for benzoate metabolism. The genome also revealed that R. ferrireducens is well-adapted for growth in the subsurface because it appears to be capable of dealing with a number of environmental insults, including heavy metals, aromatic compounds, nutrient limitation and oxidative stress. CONCLUSION: This study demonstrates that combining genome-scale modeling with the annotation of a new genome sequence can guide experimental studies and accelerate the understanding of the physiology of under-studied yet environmentally relevant microorganisms.

Genome degradation in Brucella ovis corresponds with narrowing of its host range and tissue tropism.

Brucella ovis is a veterinary pathogen associated with epididymitis in sheep. Despite its genetic similarity to the zoonotic pathogens B. abortus, B. melitensis and B. suis, B. ovis does not cause zoonotic disease. Genomic analysis of the type strain ATCC25840 revealed a high percentage of pseudogenes and increased numbers of transposable elements compared to the zoonotic Brucella species, suggesting that genome degradation has occurred concomitant with narrowing of the host range of B. ovis. The absence of genomic island 2, encoding functions required for lipopolysaccharide biosynthesis, as well as inactivation of genes encoding urease, nutrient uptake and utilization, and outer membrane proteins may be factors contributing to the avirulence of B. ovis for humans. A 26.5 kb region of B. ovis ATCC25840 Chromosome II was absent from all the sequenced human pathogenic Brucella genomes, but was present in all of 17 B. ovis isolates tested and in three B. ceti isolates, suggesting that this DNA region may be of use for differentiating B. ovis from other Brucella spp. This is the first genomic analysis of a non-zoonotic Brucella species. The results suggest that inactivation of genes involved in nutrient acquisition and utilization, cell envelope structure and urease may have played a role in narrowing of the tissue tropism and host range of B. ovis.

On the chimeric nature, thermophilic origin, and phylogenetic placement of the Thermotogales.

Since publication of the first Thermotogales genome, Thermotoga maritima strain MSB8, single- and multi-gene analyses have disagreed on the phylogenetic position of this order of Bacteria. Here we present the genome sequences of 4 additional members of the Thermotogales (Tt. petrophila, Tt. lettingae, Thermosipho melanesiensis, and Fervidobacterium nodosum) and a comprehensive comparative analysis including the original T. maritima genome. While ribosomal protein genes strongly place Thermotogales as a sister group to Aquificales, the majority of genes with sufficient phylogenetic signal show affinities to Archaea and Firmicutes, especially Clostridia. Indeed, on the basis of the majority of genes in their genomes (including genes that are also found in Aquificales), Thermotogales should be considered members of the Firmicutes. This result highlights the conflict between the taxonomic goal of assigning every species to a unique position in an inclusive Linnaean hierarchy and the evolutionary goal of understanding phylogenesis in the presence of pervasive horizontal gene transfer (HGT) within prokaryotes. Amino acid compositions of reconstructed ancestral sequences from 423 gene families suggest an origin of this gene pool even more thermophilic than extant members of this order, followed by adaptation to lower growth temperatures within the Thermotogales.

Three genomes from the phylum Acidobacteria provide insight into the lifestyles of these microorganisms in soils.

The complete genomes of three strains from the phylum Acidobacteria were compared. Phylogenetic analysis placed them as a unique phylum. They share genomic traits with members of the Proteobacteria, the Cyanobacteria, and the Fungi. The three strains appear to be versatile heterotrophs. Genomic and culture traits indicate the use of carbon sources that span simple sugars to more complex substrates such as hemicellulose, cellulose, and chitin. The genomes encode low-specificity major facilitator superfamily transporters and high-affinity ABC transporters for sugars, suggesting that they are best suited to low-nutrient conditions. They appear capable of nitrate and nitrite reduction but not N(2) fixation or denitrification. The genomes contained numerous genes that encode siderophore receptors, but no evidence of siderophore production was found, suggesting that they may obtain iron via interaction with other microorganisms. The presence of cellulose synthesis genes and a large class of novel high-molecular-weight excreted proteins suggests potential traits for desiccation resistance, biofilm formation, and/or contribution to soil structure. Polyketide synthase and macrolide glycosylation genes suggest the production of novel antimicrobial compounds. Genes that encode a variety of novel proteins were also identified. The abundance of acidobacteria in soils worldwide and the breadth of potential carbon use by the sequenced strains suggest significant and previously unrecognized contributions to the terrestrial carbon cycle. Combining our genomic evidence with available culture traits, we postulate that cells of these isolates are long-lived, divide slowly, exhibit slow metabolic rates under low-nutrient conditions, and are well equipped to tolerate fluctuations in soil hydration.

Complete genome sequence of the N2-fixing broad host range endophyte Klebsiella pneumoniae 342 and virulence predictions verified in mice.

We report here the sequencing and analysis of the genome of the nitrogen-fixing endophyte, Klebsiella pneumoniae 342. Although K. pneumoniae 342 is a member of the enteric bacteria, it serves as a model for studies of endophytic, plant-bacterial associations due to its efficient colonization of plant tissues (including maize and wheat, two of the most important crops in the world), while maintaining a mutualistic relationship that encompasses supplying organic nitrogen to the host plant. Genomic analysis examined K. pneumoniae 342 for the presence of previously identified genes from other bacteria involved in colonization of, or growth in, plants. From this set, approximately one-third were identified in K. pneumoniae 342, suggesting additional factors most likely contribute to its endophytic lifestyle. Comparative genome analyses were used to provide new insights into this question. Results included the identification of metabolic pathways and other features devoted to processing plant-derived cellulosic and aromatic compounds, and a robust complement of transport genes (15.4%), one of the highest percentages in bacterial genomes sequenced. Although virulence and antibiotic resistance genes were predicted, experiments conducted using mouse models showed pathogenicity to be attenuated in this strain. Comparative genomic analyses with the presumed human pathogen K. pneumoniae MGH78578 revealed that MGH78578 apparently cannot fix nitrogen, and the distribution of genes essential to surface attachment, secretion, transport, and regulation and signaling varied between each genome, which may indicate critical divergences between the strains that influence their preferred host ranges and lifestyles (endophytic plant associations for K. pneumoniae 342 and presumably human pathogenesis for MGH78578). Little genome information is available concerning endophytic bacteria. The K. pneumoniae 342 genome will drive new research into this less-understood, but important category of bacterial-plant host relationships, which could ultimately enhance growth and nutrition of important agricultural crops and development of plant-derived products and biofuels.

Insights into plant cell wall degradation from the genome sequence of the soil bacterium Cellvibrio japonicus.

The plant cell wall, which consists of a highly complex array of interconnecting polysaccharides, is the most abundant source of organic carbon in the biosphere. Microorganisms that degrade the plant cell wall synthesize an extensive portfolio of hydrolytic enzymes that display highly complex molecular architectures. To unravel the intricate repertoire of plant cell wall-degrading enzymes synthesized by the saprophytic soil bacterium Cellvibrio japonicus, we sequenced and analyzed its genome, which predicts that the bacterium contains the complete repertoire of enzymes required to degrade plant cell wall and storage polysaccharides. Approximately one-third of these putative proteins (57) are predicted to contain carbohydrate binding modules derived from 13 of the 49 known families. Sequence analysis reveals approximately 130 predicted glycoside hydrolases that target the major structural and storage plant polysaccharides. In common with that of the colonic prokaryote Bacteroides thetaiotaomicron, the genome of C. japonicus is predicted to encode a large number of GH43 enzymes, suggesting that the extensive arabinose decorations appended to pectins and xylans may represent a major nutrient source, not just for intestinal bacteria but also for microorganisms that occupy terrestrial ecosystems. The results presented here predict that C. japonicus possesses an extensive range of glycoside hydrolases, lyases, and esterases. Most importantly, the genome of C. japonicus is remarkably similar to that of the gram-negative marine bacterium, Saccharophagus degradans 2-40(T). Approximately 50% of the predicted C. japonicus plant-degradative apparatus appears to be shared with S. degradans, consistent with the utilization of plant-derived complex carbohydrates as a major substrate by both organisms.

Genome sequence and identification of candidate vaccine antigens from the animal pathogen Dichelobacter nodosus.

Dichelobacter nodosus causes ovine footrot, a disease that leads to severe economic losses in the wool and meat industries. We sequenced its 1.4-Mb genome, the smallest known genome of an anaerobe. It differs markedly from small genomes of intracellular bacteria, retaining greater biosynthetic capabilities and lacking any evidence of extensive ongoing genome reduction. Comparative genomic microarray studies and bioinformatic analysis suggested that, despite its small size, almost 20% of the genome is derived from lateral gene transfer. Most of these regions seem to be associated with virulence. Metabolic reconstruction indicated unsuspected capabilities, including carbohydrate utilization, electron transfer and several aerobic pathways. Global transcriptional profiling and bioinformatic analysis enabled the prediction of virulence factors and cell surface proteins. Screening of these proteins against ovine antisera identified eight immunogenic proteins that are candidate antigens for a cross-protective vaccine.

Secrets of soil survival revealed by the genome sequence of Arthrobacter aurescens TC1.

Arthrobacter sp. strains are among the most frequently isolated, indigenous, aerobic bacterial genera found in soils. Member of the genus are metabolically and ecologically diverse and have the ability to survive in environmentally harsh conditions for extended periods of time. The genome of Arthrobacter aurescens strain TC1, which was originally isolated from soil at an atrazine spill site, is composed of a single 4,597,686 basepair (bp) circular chromosome and two circular plasmids, pTC1 and pTC2, which are 408,237 bp and 300,725 bp, respectively. Over 66% of the 4,702 open reading frames (ORFs) present in the TC1 genome could be assigned a putative function, and 13.2% (623 genes) appear to be unique to this bacterium, suggesting niche specialization. The genome of TC1 is most similar to that of Tropheryma, Leifsonia, Streptomyces, and Corynebacterium glutamicum, and analyses suggest that A. aurescens TC1 has expanded its metabolic abilities by relying on the duplication of catabolic genes and by funneling metabolic intermediates generated by plasmid-borne genes to chromosomally encoded pathways. The data presented here suggest that Arthrobacter's environmental prevalence may be due to its ability to survive under stressful conditions induced by starvation, ionizing radiation, oxygen radicals, and toxic chemicals.

Skewed genomic variability in strains of the toxigenic bacterial pathogen, Clostridium perfringens.

Clostridium perfringens is a Gram-positive, anaerobic spore-forming bacterium commonly found in soil, sediments, and the human gastrointestinal tract. C. perfringens is responsible for a wide spectrum of disease, including food poisoning, gas gangrene (clostridial myonecrosis), enteritis necroticans, and non-foodborne gastrointestinal infections. The complete genome sequences of Clostridium perfringens strain ATCC 13124, a gas gangrene isolate and the species type strain, and the enterotoxin-producing food poisoning strain SM101, were determined and compared with the published C. perfringens strain 13 genome. Comparison of the three genomes revealed considerable genomic diversity with >300 unique "genomic islands" identified, with the majority of these islands unusually clustered on one replichore. PCR-based analysis indicated that the large genomic islands are widely variable across a large collection of C. perfringens strains. These islands encode genes that correlate to differences in virulence and phenotypic characteristics of these strains. Significant differences between the strains include numerous novel mobile elements and genes encoding metabolic capabilities, strain-specific extracellular polysaccharide capsule, sporulation factors, toxins, and other secreted enzymes, providing substantial insight into this medically important bacterial pathogen.

Metagenomic analysis of the human distal gut microbiome.

The human intestinal microbiota is composed of 10(13) to 10(14) microorganisms whose collective genome ("microbiome") contains at least 100 times as many genes as our own genome. We analyzed approximately 78 million base pairs of unique DNA sequence and 2062 polymerase chain reaction-amplified 16S ribosomal DNA sequences obtained from the fecal DNAs of two healthy adults. Using metabolic function analyses of identified genes, we compared our human genome with the average content of previously sequenced microbial genomes. Our microbiome has significantly enriched metabolism of glycans, amino acids, and xenobiotics; methanogenesis; and 2-methyl-d-erythritol 4-phosphate pathway-mediated biosynthesis of vitamins and isoprenoids. Thus, humans are superorganisms whose metabolism represents an amalgamation of microbial and human attributes.

Chromosome evolution in the Thermotogales: large-scale inversions and strain diversification of CRISPR sequences.

In the present study, the chromosomes of two members of the Thermotogales were compared. A whole-genome alignment of Thermotoga maritima MSB8 and Thermotoga neapolitana NS-E has revealed numerous large-scale DNA rearrangements, most of which are associated with CRISPR DNA repeats and/or tRNA genes. These DNA rearrangements do not include the putative origin of DNA replication but move within the same replichore, i.e., the same replicating half of the chromosome (delimited by the replication origin and terminus). Based on cumulative GC skew analysis, both the T. maritima and T. neapolitana lineages contain one or two major inverted DNA segments. Also, based on PCR amplification and sequence analysis of the DNA joints that are associated with the major rearrangements, the overall chromosome architecture was found to be conserved at most DNA joints for other strains of T. neapolitana. Taken together, the results from this analysis suggest that the observed chromosomal rearrangements in the Thermotogales likely occurred by successive inversions after their divergence from a common ancestor and before strain diversification. Finally, sequence analysis shows that size polymorphisms in the DNA joints associated with CRISPRs can be explained by expansion and possibly contraction of the DNA repeat and spacer unit, providing a tool for discerning the relatedness of strains from different geographic locations.

Genome analysis of multiple pathogenic isolates of Streptococcus agalactiae: implications for the microbial "pan-genome".

The development of efficient and inexpensive genome sequencing methods has revolutionized the study of human bacterial pathogens and improved vaccine design. Unfortunately, the sequence of a single genome does not reflect how genetic variability drives pathogenesis within a bacterial species and also limits genome-wide screens for vaccine candidates or for antimicrobial targets. We have generated the genomic sequence of six strains representing the five major disease-causing serotypes of Streptococcus agalactiae, the main cause of neonatal infection in humans. Analysis of these genomes and those available in databases showed that the S. agalactiae species can be described by a pan-genome consisting of a core genome shared by all isolates, accounting for approximately 80% of any single genome, plus a dispensable genome consisting of partially shared and strain-specific genes. Mathematical extrapolation of the data suggests that the gene reservoir available for inclusion in the S. agalactiae pan-genome is vast and that unique genes will continue to be identified even after sequencing hundreds of genomes.

Whole-genome sequence analysis of Pseudomonas syringae pv. phaseolicola 1448A reveals divergence among pathovars in genes involved in virulence and transposition.

Pseudomonas syringae pv. phaseolicola, a gram-negative bacterial plant pathogen, is the causal agent of halo blight of bean. In this study, we report on the genome sequence of P. syringae pv. phaseolicola isolate 1448A, which encodes 5,353 open reading frames (ORFs) on one circular chromosome (5,928,787 bp) and two plasmids (131,950 bp and 51,711 bp). Comparative analyses with a phylogenetically divergent pathovar, P. syringae pv. tomato DC3000, revealed a strong degree of conservation at the gene and genome levels. In total, 4,133 ORFs were identified as putative orthologs in these two pathovars using a reciprocal best-hit method, with 3,941 ORFs present in conserved, syntenic blocks. Although these two pathovars are highly similar at the physiological level, they have distinct host ranges; 1448A causes disease in beans, and DC3000 is pathogenic on tomato and Arabidopsis. Examination of the complement of ORFs encoding virulence, fitness, and survival factors revealed a substantial, but not complete, overlap between these two pathovars. Another distinguishing feature between the two pathovars is their distinctive sets of transposable elements. With access to a fifth complete pseudomonad genome sequence, we were able to identify 3,567 ORFs that likely comprise the core Pseudomonas genome and 365 ORFs that are P. syringae specific.

The psychrophilic lifestyle as revealed by the genome sequence of Colwellia psychrerythraea 34H through genomic and proteomic analyses.

The completion of the 5,373,180-bp genome sequence of the marine psychrophilic bacterium Colwellia psychrerythraea 34H, a model for the study of life in permanently cold environments, reveals capabilities important to carbon and nutrient cycling, bioremediation, production of secondary metabolites, and cold-adapted enzymes. From a genomic perspective, cold adaptation is suggested in several broad categories involving changes to the cell membrane fluidity, uptake and synthesis of compounds conferring cryotolerance, and strategies to overcome temperature-dependent barriers to carbon uptake. Modeling of three-dimensional protein homology from bacteria representing a range of optimal growth temperatures suggests changes to proteome composition that may enhance enzyme effectiveness at low temperatures. Comparative genome analyses suggest that the psychrophilic lifestyle is most likely conferred not by a unique set of genes but by a collection of synergistic changes in overall genome content and amino acid composition.

Gene transfer and genome plasticity in Thermotoga maritima, a model hyperthermophilic species.

The genome sequence of the hyperthermophilic bacterium Thermotoga maritima MSB8 presents evidence for lateral gene transfer events between bacterial and archaeal species. To estimate the extent of genomic diversity across the order Thermotogales, a comparative genomic hybridization study was initiated to compare nine Thermotoga strains to the sequenced T. maritima MSB8. Many differences could be associated with substrate utilization patterns, which are most likely a reflection of the environmental niche that these individual species occupy. A detailed analysis of some of the predicted variable regions demonstrates many examples of the deletion/insertion of complete cassettes of genes and of gene rearrangements and insertions of DNA within genes, with the C or N terminus being retained. Although the mechanism for gene transfer in this lineage remains to be elucidated, this analysis suggests possible associations with repetitive elements and highlights the possible benefits of rampant genetic exchange to these species.

Complete genome sequence of the plant commensal Pseudomonas fluorescens Pf-5.

Pseudomonas fluorescens Pf-5 is a plant commensal bacterium that inhabits the rhizosphere and produces secondary metabolites that suppress soilborne plant pathogens. The complete sequence of the 7.1-Mb Pf-5 genome was determined. We analyzed repeat sequences to identify genomic islands that, together with other approaches, suggested P. fluorescens Pf-5's recent lateral acquisitions include six secondary metabolite gene clusters, seven phage regions and a mobile genomic island. We identified various features that contribute to its commensal lifestyle on plants, including broad catabolic and transport capabilities for utilizing plant-derived compounds, the apparent ability to use a diversity of iron siderophores, detoxification systems to protect from oxidative stress, and the lack of a type III secretion system and toxins found in related pathogens. In addition to six known secondary metabolites produced by P. fluorescens Pf-5, three novel secondary metabolite biosynthesis gene clusters were also identified that may contribute to the biocontrol properties of P. fluorescens Pf-5.