DNA inversion in the tail fiber gene alters the host range specificity of carotovoricin Er, a phage-tail-like bacteriocin of phytopathogenic Erwinia carotovora subsp. carotovora Er

Pantailocins: phage-derived bacteriocins from Pantoea ananatis and Pantoea stewartii subsp. indologenes

IMPORTANCE

Phage-derived bacteriocins (tailocins) are ribosomally synthesized structures produced by bacteria in order to provide advantages against competing strains under natural conditions. Tailocins are highly specific in their target range and have proven to be effective for the prevention and/or treatment of bacterial diseases under clinical and agricultural settings. We describe the discovery and characterization of a new tailocin locus encoded within genomes of Pantoea ananatis and Pantoea stewartii subsp. indologenes, which may enable the development of tailocins as preventative treatments against phytopathogenic infection by these species.

Evolutionary and ecological role of extracellular contractile injection systems: from threat to weapon

Contractile injection systems (CISs) are phage tail-related structures that are encoded in many bacterial genomes. These devices encompass the cell-based type VI secretion systems (T6SSs) as well as extracellular CISs (eCISs). The eCISs comprise the R-tailocins produced by various bacterial species as well as related phage tail-like structures such as the antifeeding prophages (Afps) of Serratia entomophila, the Photorhabdus virulence cassettes (PVCs), and the metamorphosis-associated contractile structures (MACs) of Pseudoalteromonas luteoviolacea. These contractile structures are released into the extracellular environment upon suicidal lysis of the producer cell and play important roles in bacterial ecology and evolution. In this review, we specifically portray the eCISs with a focus on the R-tailocins, sketch the history of their discovery and provide insights into their evolution within the bacterial host, their structures and how they are assembled and released. We then highlight ecological and evolutionary roles of eCISs and conceptualize how they can influence and shape bacterial communities. Finally, we point to their potential for biotechnological applications in medicine and agriculture.

Isolation and Characterization of a Lytic Vibriophage OY1 and Its Biocontrol Effects Against Vibrio spp

Vibrio species are important pathogens of marine animals and aquaculture populations and some of them can cause serious infections in humans through consumption of contaminated seafood and aquaculture products. Lytic bacteriophages can potentially alleviate Vibrio contamination in the aquaculture organisms and in the processing of aquatic products and have gained significant scientific attention in recent years. In the present study, bacteriophages were isolated from sewage of local aquatic products markets and grown using Vibrio mimicus CICC 21613 as host cells. The lytic vibriophage OY1 belonging to the newly proposed family Autographiviridae and the genus Maculvirus was identified by observation under electron microscope and comparative genomic analysis. The phage OY1 showed lytic activity against 24 among 32 tested strains belonging to eight Vibrio species. The complete phage OY1 genome consists of a single circular double-stranded DNA of 43,479 bp with a total GC content of 49.27% and was predicted to encode 40 open reading frames (ORFs). To evaluate its potential against vibrios, the one-step growth curve, thermal and pH stability, host range, and lytic activity of the OY1 phage against Vibrio species were evaluated. The results showed that phage OY1 had a range of thermal and pH tolerance, and exhibited a significant inhibitory effect on the growth of tested Vibrio species. Bacterial growth in the fish muscle extract juice (FMEJ) inoculated with Vibrio mimicus CICC 21613, Vibrio parahaemolyticus CICC 21617, Vibrio alginolyticus VJ14, and the mixed bacterial culture was reduced by 2.65 log CFU/ml, 2.42 log CFU/ml, 1.93 log CFU/ml, and 2.01 log CFU/ml, respectively, by incubation with phage OY1 at 25°C for 36 h. Phage OY1 also showed a strong ability to prevent biofilm formation and destroy formed Vibrio species biofilms. These results indicate that phage OY1 is a potential biocontrol agent against Vibrio species in the aquaculture industry and in food safety control.

Bacteriocins Targeting Gram-Negative Phytopathogenic Bacteria: Plantibiotics of the Future

Gram-negative phytopathogenic bacteria are a significant threat to food crops. These microbial invaders are responsible for a plethora of plant diseases and can be responsible for devastating losses in crops such as tomatoes, peppers, potatoes, olives, and rice. Current disease management strategies to mitigate yield losses involve the application of chemicals which are often harmful to both human health and the environment. Bacteriocins are small proteinaceous antibiotics produced by bacteria to kill closely related bacteria and thereby establish dominance within a niche. They potentially represent a safer alternative to chemicals when used in the field. Bacteriocins typically show a high degree of selectivity toward their targets with no off-target effects. This review outlines the current state of research on bacteriocins active against Gram-negative phytopathogenic bacteria. Furthermore, we will examine the feasibility of weaponizing bacteriocins for use as a treatment for bacterial plant diseases.

Pseudomonas chlororaphis Produces Multiple R-Tailocin Particles That Broaden the Killing Spectrum and Contribute to Persistence in Rhizosphere Communities

R-tailocins are high-molecular-weight bacteriocins resembling bacteriophage tails. Pseudomonas chlororaphis 30-84 is a plant growth-promoting rhizobacterial (PGPR) strain that produces two distinct R-tailocin particles with different killing spectra. The two R-tailocins have different evolutionary histories but are released by the same lysis cassette. A previous study showed that both tailocins are important for pairwise competition with susceptible rhizosphere-colonizing strains; however, the broader role of tailocins in competition with the native rhizosphere microbiome was not tested. Genomic analysis of the P. chlororaphis 30-84 R-tailocin gene cluster uncovered the presence of three tail fiber genes in the tailocin 2 genetic module that could potentially result in tailocin 2 particles having different tail fibers and thus a wider killing spectrum. In this study, the tail fibers were found to incorporate onto different tailocin 2 particles, each with a distinct killing spectrum. A loss of production of one or both tailocins resulted in decreased P. chlororaphis 30-84 persistence within the wheat rhizosphere when in competition with the native microflora but not bulk soil. The capacity to produce three different versions of a single tailocin, each having one of three different types of tail fibers, is a previously unreported mechanism that leads to a broader R-tailocin killing spectrum. This study also provides evidence for the function of R-tailocins in competition with rhizosphere microbiome communities but not in bulk soil.IMPORTANCE Although R-tailocin gene clusters typically encode one tail fiber protein, three tail fiber-resembling genes were identified in association with one of the two sets of R-tailocin genes within the tailocin cluster of P. chlororaphis 30-84 and other sequenced P. chlororaphis strain genomes. This study confirmed that P. chlororaphis 30-84 not only produces two distinct tailocins, but that one of them is produced with three different types of tail fibers. This is a previously unreported strategy to increase the breadth of strains targeted by an R-tailocin. Our finding that R-tailocins produced by a PGPR Pseudomonas strain enhanced its persistence within the wheat rhizosphere microbiome confirms that R-tailocin production contributes to the population dynamics of rhizobacterial communities.

R-type bacteriocins in related strains of Xenorhabdus bovienii: Xenorhabdicin tail fiber modularity and contribution to competitiveness

R-type bacteriocins are contractile phage tail-like structures that are bactericidal towards related bacterial species. The C-terminal region of the phage tail fiber protein determines target-binding specificity. The mutualistic bacteria Xenorhabdus nematophila and X. bovienii produce R-type bacteriocins (xenorhabdicins) that are selectively active against different Xenorhabdus species. We analyzed the P2-type remnant prophage clusters in draft sequences of nine strains of X. bovienii The C-terminal tail fiber region in each of the respective strains was unique and consisted of mosaics of modular units. The region between the main tail fiber gene (xbpH1) and the sheath gene (xbpS1) contained a variable number of modules encoding tail fiber fragments. DNA inversion and module exchange between strains was involved in generating tail fiber diversity. Xenorhabdicin-enriched fractions from three different X. bovienii strains isolated from the same nematode species displayed distinct activities against each other. In one set of strains, the strain that produced highly active xenorhabdicin was able to eliminate a sensitive strain. In contrast, xenorhabdicin activity was not a determining factor in the competitive fitness of a second set of strains. These findings suggest that related strains of X. bovienii use xenorhabdicin and additional antagonistic molecules to compete against each other.

F-Type Bacteriocins of Listeria monocytogenes: a New Class of Phage Tail-Like Structures Reveals Broad Parallel Coevolution between Tailed Bacteriophages and High-Molecular-Weight Bacteriocins

Listeria monocytogenes is a significant foodborne human pathogen that can cause severe disease in certain high-risk individuals. L. monocytogenes is known to produce high-molecular-weight, phage tail-like bacteriocins, or "monocins," upon induction of the SOS system. In this work, we purified and characterized monocins and found them to be a new class of F-type bacteriocins. The L. monocytogenes monocin genetic locus was cloned and expressed in Bacillus subtilis, producing specifically targeted bactericidal particles. The receptor binding protein, which determines target cell specificity, was identified and engineered to change the bactericidal spectrum. Unlike the F-type pyocins of Pseudomonas aeruginosa, which are related to lambda-like phage tails, monocins are more closely related to TP901-1-like phage tails, structures not previously known to function as bacteriocins. Monocins therefore represent a new class of phage tail-like bacteriocins. It appears that multiple classes of phage tails and their related bacteriocins have coevolved separately in parallel.

IMPORTANCE

Phage tail-like bacteriocins (PTLBs) are structures widespread among the members of the bacterial kingdom that are evolutionarily related to the DNA delivery organelles of phages (tails). We identified and characterized "monocins" of Listeria monocytogenes and showed that they are related to the tail structures of TP901-1-like phages, structures not previously known to function as bacteriocins. Our results show that multiple types of envelope-penetrating machines have coevolved in parallel to function either for DNA delivery (phages) or as membrane-disrupting bacteriocins. While it has commonly been assumed that these structures were coopted from phages, we cannot rule out the opposite possibility, that ancient phages coopted complex bacteriocins from the cell, which then underwent adaptations to become efficient at translocating DNA.

Systematic identification and quantification of phase variation in commensal and pathogenic Escherichia coli

Bacteria have been shown to generate constant genetic variation in a process termed phase variation. We present a tool based on whole genome sequencing that allows detection and quantification of coexisting genotypes mediated by genomic inversions in bacterial cultures. We tested our method on widely used strains of Escherichia coli, and detected stable and reproducible phase variation in several invertible loci. These are shown here to be responsible for maintaining constant variation in populations grown from a single colony. Applying this tool on other bacterial strains can shed light on how pathogens adjust to hostile environments by diversifying their genomes.

The complete genome sequence of EC1-UPM, a novel N4-like bacteriophage that infects Escherichia coli O78:K80

BACKGROUND

Bacteriophage EC1-UPM is an N4-like bacteriophage which specifically infects Escherichia coli O78:K80, an avian pathogenic strain that causes colibacillosis in poultry. The complete genome sequence of bacteriophage EC1-UPM was analysed and compared with other closely related N4-like phage groups to assess their genetic similarities and differences.

RESULTS

Bacteriophage EC1-UPM displays a very similar codon usage profile with its host and does not contain any tRNA gene. Comparative genomics analysis reveals close resemblance of bacteriophage EC1-UPM to three N4-like bacteriophages namely vB_EcoP_G7C, IME11 and KBNP21 with a total of 44 protein coding genes shared at 70% identity threshold. The genomic region coding for the tail fiber protein was found to be unique in bacteriophage EC1-UPM. Further annotation of the tail fiber protein using HHpred, a highly sensitive homology detection tool, reveals the presence of protein structure homologous to various polysaccharide processing proteins in its C-terminus. Leveraging on the availability of multiple N4-like bacteriophage genome sequences, the core genes of N4-like bacteriophages were identified and used to perform a multilocus phylogenetic analysis which enabled the construction of a phylogenetic tree with higher confidence than phylogenetic trees based on single genes.

CONCLUSION

We report for the first time the complete genome sequence of a N4-like bacteriophage which is lytic against avian pathogenic Escherichia coli O78:K80. A novel 928 amino acid residues tail fiber protein was identified in EC1-UPM which may be useful to further the understanding of phage-host specificity. Multilocus phylogenetic analysis using core genes of sequenced N4-like phages showed that the evolutionary relationship correlated well with the pattern of host specificity.

Mapping and regulation of genes within Salmonella pathogenicity island 12 that contribute to in vivo fitness of Salmonella enterica Serovar Typhimurium

Salmonella pathogenicity island 12 (SPI-12) of Salmonella enterica serovar Typhimurium is a 15-kb region that encompasses genes STM2230 to STM2245 and encodes a remnant phage known to contribute to bacterial virulence. In mouse infection experiments and replication assays in macrophages, we demonstrated a role for four genes in SPI-12 for bacterial survival in the host. STM2239, a potential Q antiterminator, showed a prominent contribution to bacterial fitness. Transcriptional reporter experiments, quantitative reverse transcription-PCR (RT-PCR), and immunoblotting demonstrated that the virulence regulator SsrB and STM2239 contribute to transcriptional activation of genes in SPI-12. SsrB was found to indirectly regulate this locus by transcriptional read-through from the sspH2 (STM2241) promoter. Chromatin immunoprecipitation showed that STM2239 copurified with the promoter regulating STM2237, suggesting that STM2239 may function as an antiterminator to activate adjacent genes. These results demonstrate that bacteriophage genes may be adapted by pathogenic bacteria to improve fitness in the host.

Comparative analysis of P2-type remnant prophage loci in Xenorhabdus bovienii and Xenorhabdus nematophila required for xenorhabdicin production

The xnp1 remnant P2-type prophage of Xenorhabdus nematophila produces xenorhabdicin that is active against closely related species. Xenorhabdicin had not been characterized previously in other Xenorhabdus species. Here, we show xenorhabdicin production in six different strains of Xenorhabdus bovienii. The sequenced genome of X. bovienii SS-2004 was found to possess a highly conserved remnant P2-type cluster (xbp1). Inactivation of the xbpS1 sheath gene resulted in loss of bacteriocin activity, indicating that the xbp1 locus was required for xenorhabdicin production. xbp1 and xnp1 contain a CI-type repressor, a dinI gene involved in stabilization of ssDNA-RecA complexes and are inducible with mitomycin C, suggesting that both loci are regulated by cleavage of the CI repressor. Both xnp1 and xbp1 lack typical P2-type lysis genes but contain a predicted endolysin gene (enp) that may be involved in cell lysis. The main tail fibers of xnp1 and xbp1 are mosaic structures with divergent C-terminal regions suggesting they differ in host specificity. Several genes encoding C-terminal tail fiber fragments are present in the same position in xnp1 and xbp1. Recombination between the main fiber genes and the C-terminal fragments could potentially expand the host range specificity of xenorhabdicin in the respective strains.

Tasmancin and lysogenic bacteriophages induced from Erwinia tasmaniensis strains

Mitomycin C treatment of Erwinia tasmaniensis strains from Australia induced prophages and the expression of bacteriocins. The bacteriocin named tasmancin inhibited E. tasmaniensis strains from South Africa and Germany. A gene cluster with a klebicin-related operon and an immunity protein was detected on plasmid pET46 from E. tasmaniensis strain Et1/99. PCR reactions using primers directed to this region produced signals for several strains originating from Australia, but not for strains isolated in South Africa and Germany. The latter isolates lacked plasmid pET46. Bacteriophages were induced from E. tasmaniensis strains Et88 and Et14/99, both isolates from South-Eastern Australia. These phages formed plaques on several other strains from this region, as well as on E. tasmaniensis strains from South Africa and Germany. Sequencing revealed similarity of phages ϕEt88 and ϕEt14, which shared the host range on E. tasmaniensis strains. Bacteriophages and tasmancin may interfere with the viability of several related E. tasmaniensis strains in the environment of carrier strains.

The xnp1 P2-like tail synthesis gene cluster encodes xenorhabdicin and is required for interspecies competition

Xenorhabdus nematophila, the mutualistic bacterium of the nematode Steinernema carpocapsae, produces the R-type bacteriocin called xenorhabdicin, which is thought to confer a competitive advantage for growth in the insect host. We have identified a P2-like tail synthesis gene cluster (xnp1) that is required for xenorhabdicin production. The xnp1 genes were expressed constitutively during growth and were induced by mitomycin C. Deletion of either the sheath (xnpS1) or fiber (xnpH1) genes eliminated xenorhabdicin production. Production of R-type bacteriocins in a host organism had not been shown previously. We show that xenorhabdicin is produced in the hemocoel of insects infected with the wild type but not with the ΔxnpS1 deletion strain. Xenorhabdicin prepared from the wild-type strain killed the potential competitor Photorhabdus luminescens TT01. P. luminescens was eliminated during coculture with wild-type X. nematophila but not with the ΔxnpS1 strain. Furthermore, P. luminescens inhibited reproduction of S. carpocapsae in insect larvae, while coinjection with wild-type X. nematophila, but not the ΔxnpS1, strain restored normal reproduction, demonstrating that xenorhabdicin was required for killing P. luminescens and protecting the nematode partner. Xenorhabdicin killed X. nematophila from Steinernema anatoliense, demonstrating for the first time that it possesses intraspecies activity. In addition, activity was variable against diverse strains of Xenorhabdus and Photorhabdus and was not correlated with phylogenetic distance. These findings are discussed in the context of the role of xenorhabdicin in the life cycle of the mutualistic bacterium X. nematophila.

Niche-specificity and the variable fraction of the Pectobacterium pan-genome

We compare genome sequences of three closely related soft-rot pathogens that vary in host range and geographical distribution to identify genetic differences that could account for lifestyle differences. The isolates compared, Pectobacterium atrosepticum SCRI1043, P. carotovorum WPP14, and P. brasiliensis 1692, represent diverse lineages of the genus. P. carotovorum and P. brasiliensis genome contigs, generated by 454 pyrosequencing ordered by reference to the previously published complete circular chromosome of P. atrosepticum genome and each other, account for 96% of the predicted genome size. Orthologous proteins encoded by P. carotovorum and P. brasiliensis are approximately 95% identical to each other and 92% identical to P. atrosepticum. Multiple alignment using Mauve identified a core genome of 3.9 Mb conserved among these Pectobacterium spp. Each core genome is interrupted at many points by species-specific insertions or deletions (indels) that account for approximately 0.9 to 1.1 Mb. We demonstrate that the presence of a hrpK-like type III secretion system-dependent effector protein in P. carotovorum and P. brasiliensis and its absence from P. atrosepticum is insufficient to explain variability in their response to infection in a plant. Additional genes that vary among these species include those encoding peptide toxin production, enzyme production, secretion proteins, and antibiotic production, as well as differences in more general aspects of gene regulation and metabolism that may be relevant to pathogenicity.

Binding sequences for RdgB, a DNA damage-responsive transcriptional activator, and temperature-dependent expression of bacteriocin and pectin lyase genes in Pectobacterium carotovorum subsp. carotovorum

Pectobacterium carotovorum subsp. carotovorum strain Er simultaneously produces the phage tail-like bacteriocin carotovoricin (Ctv) and pectin lyase (Pnl) in response to DNA-damaging agents. The regulatory protein RdgB of the Mor/C family of proteins activates transcription of pnl through binding to the promoter. However, the optimal temperature for the synthesis of Ctv (23 degrees C) differs from that for synthesis of Pnl (30 degrees C), raising the question of whether RdgB directly activates ctv transcription. Here we report that RdgB directly regulates Ctv synthesis. Gel mobility shift assays demonstrated RdgB binding to the P(0), P(1), and P(2) promoters of the ctv operons, and DNase I footprinting determined RdgB-binding sequences (RdgB boxes) on these and on the pnl promoters. The RdgB box of the pnl promoter included a perfect 7-bp inverted repeat with high binding affinity to the regulator (K(d) [dissociation constant] = 150 nM). In contrast, RdgB boxes of the ctv promoters contained an imperfect inverted repeat with two or three mismatches that consequently reduced binding affinity (K(d) = 250 to 350 nM). Transcription of the rdgB and ctv genes was about doubled at 23 degrees C compared with that at 30 degrees C. In contrast, the amount of pnl transcription tripled at 30 degrees C. Thus, the inverse synthesis of Ctv and Pnl as a function of temperature is apparently controlled at the transcriptional level, and reduced rdgB expression at 30 degrees C obviously affected transcription from the ctv promoters with low-affinity RdgB boxes. Pathogenicity toward potato tubers was reduced in an rdgB knockout mutant, suggesting that the RdgAB system contributes to the pathogenicity of this bacterium, probably by activating pnl expression.

Cloning and expression of the Erwinia carotovora subsp. carotovora gene encoding the low-molecular-weight bacteriocin carocin S1

The purpose of this study was to clone the carocin S1 gene and express it in a non-carocin-producing strain of Erwinia carotovora. A mutant, TH22-10, which produced a high-molecular-weight bacteriocin but not a low-molecular-weight bacteriocin, was obtained by Tn5 insertional mutagenesis using H-rif-8-2 (a spontaneous rifampin-resistant mutant of Erwinia carotovora subsp. carotovora 89-H-4). Using thermal asymmetric interlaced PCR, the DNA sequence from the Tn5 insertion site and the DNA sequence of the contiguous 2,280-bp region were determined. Two complete open reading frames (ORF), designated ORF2 and ORF3, were identified within the sequence fragment. ORF2 and ORF3 were identified with the carocin S1 genes, caroS1K (ORF2) and caroS1I (ORF3), which, respectively, encode a killing protein (CaroS1K) and an immunity protein (CaroS1I). These genes were homologous to the pyocin S3 gene and the pyocin AP41 gene. Carocin S1 was expressed in E. carotovora subsp. carotovora Ea1068 and replicated in TH22-10 but could not be expressed in Escherichia coli (JM101) because a consensus sequence resembling an SOS box was absent. A putative sequence similar to the consensus sequence for the E. coli cyclic AMP receptor protein binding site (-312 bp) was found upstream of the start codon. Production of this bacteriocin was also induced by glucose and lactose. The homology search results indicated that the carocin S1 gene (between bp 1078 and bp 1704) was homologous to the pyocin S3 and pyocin AP41 genes in Pseudomonas aeruginosa. These genes encode proteins with nuclease activity (domain 4). This study found that carocin S1 also has nuclease activity.

Cloning and sequencing of a genomic island found in the Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius

A genomic island was identified in the Haemophilus influenzae biogroup aegyptius Brazilian purpuric fever (BPF) strain F3031. This island, which was also found in other BPF isolates, could not be detected in non-BPF biogroup aegyptius strains or in nontypeable or typeable H. influenzae strains, with the exception of a region present in the type b Eagan strain. This 34,378-bp island is inserted, in reference to H. influenzae Rd KW20, within a choline transport gene and contains a mosaic structure of Mu-like prophage genes, several hypothetical genes, and genes potentially encoding an Erwinia carotovora carotovoricin Er-like bacteriocin. The product of the tail fiber ORF in the bacteriocin-like region shows a hybrid structure where the C terminus is similar to an H. influenzae phage HP1 tail protein implicating this open reading frame in altering host specificity for a putative bacteriocin. Significant synteny is seen in the entire genomic island with genomic regions from Salmonella enterica subsp. enterica serovar Typhi CT18, Photorhabdus luminescens subsp. laumondii TT01, Chromobacterium violaceum, and to a lesser extent Haemophilus ducreyi 35000HP. In a previous work, we isolated several BPF-specific DNA fragments through a genome subtraction procedure, and we have found that a majority of these fragments map to this locus. In addition, several subtracted fragments generated from an independent laboratory by using different but related strains also map to this island. These findings underscore the importance of this BPF-specific chromosomal region in explaining some of the genomic differences between highly invasive BPF strains and non-BPF isolates of biogroup aegyptius.

Molecular characterization of Brucella abortus chromosome II recombination

Large-scale genomic rearrangements including inversions, deletions, and duplications are significant in bacterial evolution. The recently completed Brucella melitensis 16M and Brucella suis 1330 genomes have facilitated the investigation of such events in the Brucella spp. Suppressive subtractive hybridization (SSH) was employed in identifying genomic differences between B. melitensis 16M and Brucella abortus 2308. Analysis of 45 SSH clones revealed several deletions on chromosomes of B. abortus and B. melitensis that encoded proteins of various metabolic pathways. A 640-kb inversion on chromosome II of B. abortus has been reported previously (S. Michaux Charachon, G. Bourg, E. Jumas Bilak, P. Guigue Talet, A. Allardet Servent, D. O'Callaghan, and M. Ramuz, J. Bacteriol. 179:3244-3249, 1997) and is further described in this study. One end of the inverted region is located on a deleted TATGC site between open reading frames BMEII0292 and BMEII0293. The other end inserted at a GTGTC site of the cyclic-di-GMP phosphodiesterase A (PDEA) gene (BMEII1009), dividing PDEA into two unequal DNA segments of 160 and 977 bp. As a consequence of inversion, the 160-bp segment that encodes the N-terminal region of PDEA was relocated at the opposite end of the inverted chromosomal region. The splitting of the PDEA gene most likely inactivated the function of this enzyme. A recombination mechanism responsible for this inversion is proposed.

Genomic analysis of the F3031 Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius by PCR-based subtractive hybridization

PCR-based subtractive genome hybridization produced clones harboring inserts present in Brazilian purpuric fever (BPF) prototype strain F3031 but absent in noninvasive Haemophilus influenzae biogroup aegyptius isolate F1947. Some of these inserts have no matches in the GenBank database, while others are similar to genes encoding either known or hypothetical proteins. One insert represents a 2.3-kb locus with similarity to a Thermotoga maritima hypothetical protein, while another is part of a 7.6-kb locus that contains predicted genes encoding hypothetical, phage-related, and carotovoricin Er-like proteins. The presence of DNA related to these loci is variable among BPF isolates and nontypeable H. influenzae strains, while neither of them was detected in strains of types a to f. The data indicate that BPF-causing strain F3031 harbors unique chromosomal regions, most of which appear to be acquired from unrelated microbial sources.

Temperature-dependent production of carotovoricin Er and pectin lyase in phytopathogenic Erwinia carotovora subsp. carotovora Er

The production of pectin lyase (Pnl) and carotovoricin (Ctv), as well as cell lysis in the plant-pathogenic bacterium Erwinia carotovora subsp. carotovora Er are induced by mitomycin C. Here, Pnl and Ctv production and cell lysis were found to be temperature-dependent. The optimal temperature for Pnl production was 30 degrees C. However, the optimal temperature for both Ctv production and cell lysis was 23 degrees C, at which Pnl production was reduced to 47% of the maximum. These data suggest the possible existence of novel regulation system(s) for the production of Pnl and Ctv, and cell lysis, in addition to the well-documented regulation system of recA, rdgA, and rdgB genes.