Intergeneric transfer of conjugative and mobilizable plasmids harbored by Escherichia coli in the gut of the soil microarthropod Folsomia candida (Collembola)

Models for Gut-Mediated Horizontal Gene Transfer by Bacterial Plasmid Conjugation

The emergence of new antimicrobial resistant and virulent bacterial strains may pose a threat to human and animal health. Bacterial plasmid conjugation is a significant contributor to rapid microbial evolutions that results in the emergence and spread of antimicrobial resistance (AR). The gut of animals is believed to be a potent reservoir for the spread of AR and virulence genes through the horizontal exchange of mobile genetic elements such as plasmids. The study of the plasmid transfer process in the complex gut environment is limited due to the confounding factors that affect colonization, persistence, and plasmid conjugation. Furthermore, study of plasmid transfer in the gut of humans is limited to observational studies, leading to the need to identify alternate models that provide insight into the factors regulating conjugation in the gut. This review discusses key studies on the current models for in silico, in vitro, and in vivo modeling of bacterial conjugation, and their ability to reflect the gut of animals. We particularly emphasize the use of computational and in vitro models that may approximate aspects of the gut, as well as animal models that represent in vivo conditions to a greater extent. Directions on future research studies in the field are provided.

Membrane Vesicles Produced by Shewanella vesiculosa HM13 as a Prospective Platform for Secretory Production of Heterologous Proteins at Low Temperatures

Extracellular membrane vesicles (EMVs) produced by Gram-negative bacteria are useful as a vaccine platform. During growth in broth at 18 °C, Shewanella vesiculosa HM13 produces a large number of EMVs that contain a 49-kDa major cargo protein, named P49. Enhanced green fluorescent protein fused to the C-terminus of P49 is delivered to EMVs, suggesting that P49 is useful as a carrier to target foreign proteins to EMVs for production of artificial EMVs with desired functions. This method is potentially useful for the preparation of designed vaccines and is described in detail in this chapter.

Pathways for horizontal gene transfer in bacteria revealed by a global map of their plasmids

Plasmids can mediate horizontal gene transfer of antibiotic resistance, virulence genes, and other adaptive factors across bacterial populations. Here, we analyze genomic composition and pairwise sequence identity for over 10,000 reference plasmids to obtain a global map of the prokaryotic plasmidome. Plasmids in this map organize into discrete clusters, which we call plasmid taxonomic units (PTUs), with high average nucleotide identity between its members. We identify 83 PTUs in the order Enterobacterales, 28 of them corresponding to previously described archetypes. Furthermore, we develop an automated algorithm for PTU identification, and validate its performance using stochastic blockmodeling. The algorithm reveals a total of 276 PTUs in the bacterial domain. Each PTU exhibits a characteristic host distribution, organized into a six-grade scale (I–VI), ranging from plasmids restricted to a single host species (grade I) to plasmids able to colonize species from different phyla (grade VI). More than 60% of the plasmids in the global map are in groups with host ranges beyond the species barrier.

Plasmids can mediate gene transfer across bacterial populations. Here, the authors describe a global map of the prokaryotic plasmidome, where plasmids organize into discrete ‘plasmid taxonomic units’ based on their genomic composition and pairwise sequence identity.

Adsorbed Sulfamethoxazole Exacerbates the Effects of Polystyrene (∼2 μm) on Gut Microbiota and the Antibiotic Resistome of a Soil Collembolan

Microplastics pollution in the environment is now receiving worldwide attention; however, the effects of copollution of antibiotics and microplastics on the gut microbiome of globally distributed and functionally important nontarget soil animals remain poorly understood. We studied a model collembolan (Folsomia candida) and found that the ingestion of microplastics (polystyrene, 2-2.9 μm) substantially altered the gut microbiome, antibiotic resistance gene (ARG) profile, and the isotopic fractionation in the soil collembolan tissue. Importantly, collembolans exposed to polystyrene microplastics loaded with sulfamethoxazole (MA) presented a distinctive gut microbiome, ARG profile, and isotopic fractionation compared to those exposed to polystyrene alone (MH). We observed that the abundance of ARGs and mobile genetic elements (MGEs) in the MA-treated collembolan guts was significantly higher than in the MH and the control treatments. There were also strong interactions between the gut microbiome and ARGs in the collembolan guts. We further found that bacterial β-diversity correlated significantly with the δ¹³C and δ¹⁵N values in collembolan body tissues. Together, our results indicate that changes in isotopic fractionation and ARG profiles in the collembolan were induced by the changes in gut microbiota and suggest that microplastics from diverse sources may have profound influences on soil fauna and soil food webs.

Effects of diet on gut microbiota of soil collembolans

The importance of diet in regulating the gut microbiome of globally distributed and functionally important soil generalist invertebrates such as collembolans remain poorly understood. Here, we studied a model collembolan (Folsomia candida) and found that diet (bacteria, plant litters, yeast, mixed food) is a critical factor in regulating the microbial diversity and community composition of this important soil organism. Collembolans fed with litter exhibited the lowest bacterial diversity and were dominated by Ochrobactrum. Conversely, collembolans fed with mixed diets resulted in the highest bacterial diversity. Our findings further suggest that microbial communities associated with different diets are linked to different levels of collembolan fitness. For example, the relative abundance of the genera of unclassified Thermogemmatisporaceae, Brevibacillus, and Novosphingobium were positively correlated with growth of the collembolans. Together, our work provides evidence that diet is a major force controlling the gut microbiome of collembolans, and is a good environmental predictor for collembolan growth, with implications for ecosystem functioning in terrestrial environments.

Diversity and metabolic potential of the microbiota associated with a soil arthropod

Springtails are important members of the soil fauna and play a key role in plant litter decomposition, for example through stimulation of the microbial activity. However, their interaction with soil microorganisms remains poorly understood and it is unclear which microorganisms are associated to the springtail (endo) microbiota. Therefore, we assessed the structure of the microbiota of the springtail Orchesella cincta (L.) using 16S rRNA gene amplicon sequencing. Individuals were sampled across sites in the field and the microbiota and in particular the endomicrobiota were investigated. The microbiota was dominated by the families of Rickettsiaceae, Enterobacteriaceae and Comamonadaceae and at the genus level the most abundant genera included Rickettsia, Chryseobacterium, Pseudomonas, and Stenotrophomonas. Microbial communities were distinct for the interior of the springtails for measures of community diversity and exhibited structure according to collection sites. Functional analysis of the springtail bacterial community suggests that abundant members of the microbiota may be associated with metabolism including decomposition processes. Together these results add to the understanding of the microbiota of springtails and interaction with soil microorganisms including their putative functional roles.

Identification, synthesis and regulatory function of the N-acylated homoserine lactone signals produced by Pseudomonas chlororaphis HT66

BACKGROUND

Pseudomonas chlororaphis HT66 isolated from the rice rhizosphere is an important plant growth-promoting rhizobacteria that produce phenazine-1-carboxamide (PCN) in high yield. Phenazine production is regulated by a quorum sensing (QS) system that involves the N-acylated homoserine lactones (AHLs)-a prevalent type of QS molecule.

RESULTS

Three QS signals were detected by thin layer chromatography (TLC) and high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS), which identified to be N-(3-hydroxy hexanoyl)-L-homoserine lactone (3-OH-C6-HSL), N-(3-hydroxy octanoyl)-L-homoserine lactone (3-OH-C8-HSL) and N-(3-hydroxy decanoyl)-L-homoserine lactone (3-OH-C10-HSL). The signal types and methods of synthesis were different from that in other phenazine-producing Pseudomonas strains. By non-scar deletion and heterologous expression techniques, the biosynthesis of the AHL-signals was confirmed to be only catalyzed by PhzI, while other AHLs synthases i.e., CsaI and HdtS were not involved in strain HT66. In comparison to wild-type HT66, PCN production was 2.3-folds improved by over-expression of phzI, however, phzI or phzR mutant did not produce PCN. The cell growth of HT66∆phzI mutant was significantly decreased, and the biofilm formation in phzI or phzR inactivated strains of HT66 decreased to various extents.

CONCLUSION

In conclusion, the results demonstrate that PhzI-PhzR system plays a critical role in numerous biological processes including phenazine production.

Engineering and systems-level analysis of Pseudomonas chlororaphis for production of phenazine-1-carboxamide using glycerol as the cost-effective carbon source

BACKGROUND

Glycerol, an inevitable byproduct of biodiesel, has become an attractive feedstock for the production of value-added chemicals due to its availability and low price. Pseudomonas chlororaphis HT66 can use glycerol to synthesize phenazine-1-carboxamide (PCN), a phenazine derivative, which is strongly antagonistic to fungal phytopathogens. A systematic understanding of underlying mechanisms for the PCN overproduction will be important for the further improvement and industrialization.

RESULTS

We constructed a PCN-overproducing strain (HT66LSP) through knocking out three negative regulatory genes, lon, parS, and prsA in HT66. The strain HT66LSP produced 4.10 g/L of PCN with a yield of 0.23 (g/g) from glycerol, which was of the highest titer and the yield obtained among PCN-producing strains. We studied gene expression, metabolomics, and dynamic ¹³C tracer in HT66 and HT66LSP. In response to the phenotype changes, the transcript levels of phz biosynthetic genes, which are responsible for PCN biosynthesis, were all upregulated in HT66LSP. Central carbon was rerouted to the shikimate pathway, which was shown by the modulation of specific genes involved in the lower glycolysis, the TCA cycle, and the shikimate pathway, as well as changes in abundances of intracellular metabolites and flux distribution to increase the precursor availability for PCN biosynthesis. Moreover, dynamic ¹³C-labeling experiments revealed that the presence of metabolite channeling of 3-phosphoglyceric acid to phosphoenolpyruvate and shikimate to trans-2,3-dihydro-3-hydroxyanthranilic acid in HT66LSP could enable high-yielding synthesis of PCN.

CONCLUSIONS

The integrated analysis of gene expression, metabolomics, and dynamic ¹³C tracer enabled us to gain a more in-depth insight into complex mechanisms for the PCN overproduction. This study provides important basis for further engineering P. chlororaphis for high PCN production and efficient glycerol conversion.

Conjugative Plasmid Transfer in Xylella fastidiosa Is Dependent on tra and trb Operon Functions

The insect-transmitted plant pathogen Xylella fastidiosa is capable of efficient horizontal gene transfer (HGT) and recombination. Natural transformation occurs at high rates in X. fastidiosa, but there also is evidence that certain strains of X. fastidiosa carry native plasmids equipped with transfer and mobilization genes, suggesting conjugation as an additional mechanism of HGT in some instances. Two operons, tra and trb, putatively encoding a conjugative type IV secretion system, are found in some but not all X. fastidiosa isolates, often on native plasmids. X. fastidiosa strains that carry the conjugative transfer genes can belong to different subspecies and frequently differ in host ranges. Using X. fastidiosa strain M23 (X. fastidiosa subsp. fastidiosa) or Dixon (X. fastidiosa subsp. multiplex) as the donor strain and Temecula (X. fastidiosa subsp. fastidiosa) as the recipient strain, plasmid transfer was characterized using the mobilizable broad-host-range vector pBBR5pemIK. Transfer of plasmid pBBR5pemIK was observed under in vitro conditions with both donor strains and was dependent on both tra and trb operon functions. A conjugative mechanism likely contributes to gene transfer between diverse strains of X. fastidiosa, possibly facilitating adaptation to new environments or different hosts.IMPORTANCEXylella fastidiosa is an important plant pathogen worldwide, infecting a wide range of different plant species. The emergence of new diseases caused by X. fastidiosa, or host switching of existing strains, is thought to be primarily due to the high frequency of HGT and recombination in this pathogen. Transfer of plasmids by a conjugative mechanism enables movement of larger amounts of genetic material at one time, compared with other routes of gene transfer such as natural transformation. Establishing the prevalence and functionality of this mechanism in X. fastidiosa contributes to a better understanding of HGT, adaptation, and disease emergence in this diverse pathogen.

Developing genome-reduced Pseudomonas chlororaphis strains for the production of secondary metabolites

BACKGROUND

The current chassis organisms or various types of cell factories have considerable advantages and disadvantages. Therefore, it is necessary to develop various chassis for an efficient production of different bioproducts from renewable resources. In this context, synthetic biology offers unique potentialities to produce value-added products of interests. Microbial genome reduction and modification are important strategies for constructing cellular chassis and cell factories. Many genome-reduced strains from Escherichia coli, Bacillus subtilis, Corynebacterium glutamicum and Streptomyces, have been widely used for the production of amino acids, organic acids, and some enzymes. Some Pseudomonas strains could serve as good candidates for ideal chassis cells since they grow fast and can produce many valuable metabolites with low nutritional requirements and strong environmental adaptability. Pseudomonas chlororaphis GP72 is a non-pathogenic plant growth-promoting rhizobacterium that possesses capacities of tolerating various environmental stresses and synthesizing many kinds of bioactive compounds with high yield. These include phenazine-1-carboxylic acid (PCA) and 2-hydroxyphenazine (2-OH-PHZ), which exhibit strong bacteriostatic and antifungal activity toward some microbial pathogens.

RESULTS

We depleted 685 kb (10.3% of the genomic sequence) from the chromosome of P. chlororaphis GP72(rpeA-) by a markerless deletion method, which included five secondary metabolic gene clusters and 17 strain-specific regions (525 non-essential genes). Then we characterized the 22 multiple-deletion series (MDS) strains. Growth characteristics, production of phenazines and morphologies were changed greatly in mutants with large-fragment deletions. Some of the genome-reduced P. chlororaphis mutants exhibited more productivity than the parental strain GP72(rpeA-). For example, strain MDS22 had 4.4 times higher production of 2-OH-PHZ (99.1 mg/L) than strain GP72(rpeA-), and the specific 2-OH-PHZ production rate (mmol/g/h) increased 11.5-fold. Also and MDS10 had the highest phenazine production (852.0 mg/L) among all the studied strains with a relatively high specific total phenazine production rate (0.0056 g/g/h).

CONCLUSIONS

In conclusion, P. chlororaphis strains with reduced genome performed better in production of secondary metabolites than the parent strain. The newly developed mutants can be used for the further genetic manipulation to construct chassis cells with the less complex metabolic network, better regulation and more efficient productivity for diverse biotechnological applications.

Genetic engineering of Pseudomonas chlororaphis GP72 for the enhanced production of 2-Hydroxyphenazine

Background

The biocontrol strain Pseudomonas chlororaphis GP72 isolated from the green pepper rhizosphere synthesizes three antifungal phenazine compounds, 2-Hydroxyphenazine (2-OH-PHZ), 2-hydroxy-phenazine-1-carboxylic acid (2-OH-PCA) and phenazine-1-carboxylic acid (PCA). PCA has been a commercialized antifungal pesticide registered as “Shenqinmycin” in China since 2011. It is found that 2-OH-PHZ shows stronger fungistatic and bacteriostatic activity to some pathogens than PCA. 2-OH-PHZ could be developed as a potential antifungal pesticide. But the yield of 2-OH-PHZ generally is quite low, such as P. chlororaphis GP72, the production of 2-OH-PHZ by the wide-type strain is only 4.5 mg/L, it is necessary to enhance the yield of 2-OH-PHZ for its application in agriculture.

Results

Different strategies were used to improve the yield of 2-OH-PHZ: knocking out the negative regulatory genes, enhancing the shikimate pathway, deleting the competing pathways of 2-OH-PHZ synthesis based on chorismate, and improving the activity of PhzO which catalyzes the conversion of PCA to 2-OH-PHZ, although the last two strategies did not give us satisfactory results. In this study, four negative regulatory genes (pykF, rpeA, rsmE and lon) were firstly knocked out of the strain GP72 genome stepwise. The yield of 2-OH-PHZ improved more than 60 folds and increased from 4.5 to about 300 mg/L. Then six key genes (ppsA, tktA, phzC, aroB, aroD and aroE) selected from the gluconeogenesis, pentose phosphate and shikimate pathways which used to enhance the shikimate pathway were overexpressed to improve the production of 2-OH-PHZ. At last a genetically engineered strain that increased the 2-OH-PHZ production by 99-fold to 450.4 mg/L was obtained.

Conclusions

The 2-OH-PHZ production of P. chlororaphis GP72 was greatly improved through disruption of four negative regulatory genes and overexpression of six key genes, and it is shown that P. chlororaphis GP72 could be modified as a potential cell factory to produce 2-OH-PHZ and other phenazine biopesticides by genetic and metabolic engineering.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0529-0) contains supplementary material, which is available to authorized users.

Conjugative transfer of a derivative of the IncP-1α plasmid RP4 and establishment of transconjugants in the indigenous bacterial community of poplar plants

The persistence of traits introduced into the indigenous bacterial community of poplar plants was investigated using bioluminescence mediated by the luc gene. Three endophytic bacterial strains provided with the IncP-1α plasmid RP4-Tn-luc were used to inoculate poplar cuttings at different phenological stages. Screening of isolates by bioluminescence and real-time PCR detection of the luc gene revealed stable persistence for at least 10 weeks. Although the inoculated strains became established with a high population density after inoculation at leaf development (April) and senescence (October), the strains were suppressed by the indigenous bacteria at stem elongation (June). Transconjugants could be detected only at this phenological stage. Indigenous bacteria harbouring RP4-Tn-luc became established with densities ranging from 2 × 10(5) to 9 × 10(6) CFU g(-1) fresh weight 3 and 10 weeks after inoculation. The increased colonization of the cuttings by indigenous bacteria at stem elongation seemed to strongly compete with the introduced strains. Otherwise, the phenological stage of the plants as well as the density of the indigenous recipients could serve as the driver for a more frequent conjugative plasmid transfer. A phylogenetic assignment of transconjugants indicated the transfer of RP4-Tn-luc into six genera of Proteobacteria, mainly Sphingomonas, Stenotrophomonas and Xanthomonas.

The microbiome of Folsomia candida: an assessment of bacterial diversity in a Wolbachia-containing animal

The springtail Folsomia candida is an important model organism for soil ecology, ecotoxicology and ecogenomics. The decomposer activities of soil invertebrates like Folsomia depend on their relationship with microbial communities including gut symbionts. In this paper, we apply high-throughput sequencing to provide a detailed characterization of the bacterial community associated with parthenogenetic F. candida. First, we evaluated a method to suppress the amplification of DNA from the endosymbiont Wolbachia, to prevent it from interfering with the identification of less abundant operational taxonomic units (OTUs). The suppression treatment applied was effective against Wolbachia and did not interfere with the detection of the most abundant OTUs (59 OTUs, contributing over 87% of the reads). However, this method did affect the inferred community composition. Significant differences were subsequently observed in the composition of bacterial communities associated with two different strains of F. candida. A total of 832 OTUs were found, of which 45% were only present in one strain and 17% only in the other. Among the 20 most abundant OTUs, 16 were shared between strains. Denaturing gradient gel electrophoresis and clone libraries, although unable to capture the full diversity of the bacterial community, provided results that supported the NGS data.

Cargo capacity of phages and plasmids and other factors influencing horizontal transfers of prokaryote transposable elements

Horizontal transfer of transposable elements (TEs) plays a key role in prokaryote genome evolution. Most TEs do not encode the enzymatic machinery allowing them to transfer between host cells and it is widely assumed in the literature that horizontal transfer of prokaryote TEs is mediated by other mobile genetic elements such as phages and plasmids. In a recent study, we have shown that phages are less tolerant to insertion sequences (IS, the most frequent class of prokaryote TEs) and therefore have a lower cargo capacity than plasmids. Consequently, while our analysis confirmed the crucial role of plasmids as efficient vehicles of IS horizontal transfer, we concluded that phages are unlikely to efficiently shuttle IS elements between prokaryotes. Here, we discuss whether or not the distribution pattern observed for IS elements in phages and plasmids also holds for other TEs, such as transposons and mobile introns. We also further explore various factors that may impact the relative capacity of phages and plasmids to mediate TE horizontal transfer among prokaryotes.

Regulation of gene expression in Pseudomonas aeruginosa M18 by phenazine-1-carboxylic acid

Phenazine-1-carboxylic acid (PCA), an environmentally compatible redox-active metabolite produced by Pseudomonas sp., has been found to effectively protect against various phytopathogens. The objective of this study was to discover whether PCA can also act as a signaling molecule that regulates gene expression in Pseudomonas aeruginosa M18. We constructed a series of PCA-producing mutant strains (high PCA, M18MSU1; low PCA, M18MS; and no PCA, M18MSP1P2) and analyzed their gene expression by using a custom microarray DNA chip. We found that the expression of PCA in both M18MSU1 and M18MS altered the expression of a total of 545 different genes; however, the higher level of PCA in M18MSU1 altered more genes (489) than did the lower level of PCA in M18MS (129). Of particular note, 73 of these genes were commonly regulated between the two mutants, indicating their importance in the downstream function of PCA. PCA molecules upregulated genes that function primarily in energy production, cell motility, secretion, and defense mechanisms and downregulated genes involved in transcription, translation, cell division, and gene expression in the prophage. We found that PCA worked to alter the expression of an efflux pump gene mexH through a SoxR-mediated mechanism; we further hypothesized that other pathways should also be affected by this interaction. Taken together, our results provide the first evidence of PCA-derived molecular responses at the transcriptional level. They also help to elucidate the future of genetically engineered P. aeruginosa strains for the production of PCA used in a number of applications.

Biodiversity of Actinomycetes associated with Caribbean sponges and their potential for natural product discovery

Marine actinomycetes provide a rich source of structurally unique and bioactive secondary metabolites. Numerous genera of marine actinomycetes have been isolated from marine sediments as well as several sponge species. In this study, 16 different species of Caribbean sponges were collected from four different locations in the coastal waters off Puerto Rico in order to examine diversity and bioactive metabolite production of marine actinomycetes in Caribbean sponges. Sediments were also collected from each location, in order to compare actinomycete communities between these two types of samples. A total of 180 actinomycetes were isolated and identified based on 16S rRNA gene analysis. Phylogenetic analysis revealed the presence of at least 14 new phylotypes belonging to the genera Micromonospora, Verruscosispora, Streptomyces, Salinospora, Solwaraspora, Microbacterium and Cellulosimicrobium. Seventy-eight of the isolates (19 from sediments and 59 from sponges) shared 100 % sequence identity with Micromonospora sp. R1. Despite having identical 16S rRNA sequences, the bioactivity of extracts and subsequent fractions generated from the fermentation of both sponge- and sediment-derived isolates identical to Micromonospora sp. R1 varied greatly, with a marked increase in antibiotic metabolite production in those isolates derived from sponges. These results indicate that the chemical profiles of isolates with high 16S rRNA sequence homology to known strains can be diverse and dependent on the source of isolation. In addition, seven previously reported dihydroquinones produced by five different Streptomyces strains have been purified and characterized from one Streptomyces sp. strain isolated in this study from the Caribbean sponge Agelas sceptrum.

The autotransporter protein from Bordetella avium, Baa1, is involved in host cell attachment

Bordetella avium is a Gram negative upper respiratory tract pathogen of birds. B. avium infection of commercially raised turkeys is an agriculturally significant problem. Here we describe the functional analysis of the first characterized B. avium autotransporter protein, Baa1. Autotransporters comprise a large family of proteins found in all groups of Gram negative bacteria. Although not unique to pathogenic bacteria, autotransporters have been shown to perform a variety of functions implicated in virulence. To test the hypothesis that Baa1 is a B. avium virulence factor, unmarked baa1 deletion mutants (Δbaa1) were created and tested phenotypically. It was found that baa1 mutants have wild-type levels of serum sensitivity and infectivity, yet significantly lower levels of turkey tracheal cell attachment in vitro. Likewise, semi-purified recombinant His-tagged Baa1, expressed in Escherichia coli, was shown to bind specifically to turkey tracheal cells via western blot analysis. Taken together, we conclude that Baa1 acts as a host cell attachment factor and thus plays a role B. avium virulence.

Long-term Hg pollution-induced structural shifts of bacterial community in the terrestrial isopod (Porcellio scaber) gut

In previous studies we detected lower species richness and lower Hg sensitivity of the bacteria present in egested guts of Porcellio scaber (Crustacea, Isopoda) from chronically Hg polluted than from unpolluted environment. Basis for such results were further investigated by sequencing of 16S rRNA genes of mercury-resistant (Hgr) isolates and clone libraries. We observed up to 385 times higher numbers of Hgr bacteria in guts of animals from polluted than from unpolluted environment. The majority of Hgr strains contained merA genes. Sequencing of 16S rRNA clones from egested guts of animals from Hg-polluted environments showed elevated number of bacteria from Pseudomonas, Listeria and Bacteroidetes relatives groups. In animals from pristine environment number of bacteria from Achromobacter relatives, Alcaligenes, Paracoccus, Ochrobactrum relatives, Rhizobium/Agrobacterium, Bacillus and Microbacterium groups were elevated. Such bacterial community shifts in guts of animals from Hg-polluted environment could significantly contribute to P. scaber Hg tolerance.

Identification and characterization of two Bordetella avium gene products required for hemagglutination

Bordetella avium causes bordetellosis in birds, a disease similar to whooping cough caused by Bordetella pertussis in children. B. avium agglutinates guinea pig erythrocytes via an unknown mechanism. Loss of hemagglutination ability results in attenuation. We report the use of transposon mutagenesis to identify two genes required for hemagglutination. The genes (hagA and hagB) were adjacent and divergently oriented and had no orthologs in the genomes of other Bordetella species. Construction of in-frame, unmarked mutations in each gene allowed examination of the role of each in conferring erythrocyte agglutination, explanted tracheal cell adherence, and turkey poult tracheal colonization. In all of the in vitro and in vivo assays, the requirement for the trans-acting products of hagA and hagB (HagA and HagB) was readily shown. Western blotting, using antibodies to purified HagA and HagB, revealed proteins of the predicted sizes of HagA and HagB in an outer membrane-enriched fraction. Antiserum to HagB, but not HagA, blocked B. avium erythrocyte agglutination and explanted turkey tracheal ring binding. Bioinformatic analysis indicated the similarity of HagA and HagB to several two-component secretory apparatuses in which one product facilitates the exposition of the other. HagB has the potential to serve as a useful immunogen to protect turkeys against colonization and subsequent disease.

Diversity of bacteria associated with Collembola - a cultivation-independent survey based on PCR-amplified 16S rRNA genes

The bacterial communities found in eight different soil-inhabiting microarthropod species of the Class Collembola (springtails) were analyzed by analysis of PCR-amplified 16S rRNA genes obtained without cultivation from total DNA. To characterize the bacteria associated with the parthenogenetically-reproducing Folsomia candida, the almost complete 16S rRNA genes were amplified with three universal primers, i.e., the forward primer F27 and the reverse primer R1492 or R1525. With the reverse primer R1492, 100% of 49 cloned PCR products were identical to the 16S rRNA gene of the intracellular reproduction parasite Wolbachia pipientis (Supergroup E). However, no Wolbachia was detected with the reverse primer R1525 when two different breeding stocks of F. candida were analyzed. Clone libraries from one breeding stock were composed exclusively of a sequence related closely to intracellular bacteria of the genus Rickettsiella (Gammaproteobacteria) (93 clones). In contrast, this sequence was not detected in the other F. candida breeding stock. Instead, sequences of 95 clones originated from different phylogenetic groups (Alphaproteobacteria, Gammaproteobacteria, Firmicutes and Planctomycetes). Several were closely related to bacteria, which are known to live in soil and interact with insects. Genetic profiles based on PCR-amplified partial 16S rRNA genes and single-strand conformation polymorphism (SSCP) indicated that different Collembola species harbored different bacterial communities. SSCP bands indicating Wolbachia pipientis supergroup E were detected in profiles from four of the five parthenogenetic species included in this study. Other dominant bands in the SSCP profiles were related to bacteria from the phyla Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. One sequence (AJ605704) indicated the presence of a not-yet-described intracellular symbiont from the Gammaproteobacteria, but several other sequences may represent less specific interactions between environmental bacteria and Collembola.

Conjugative transfer of plasmid-located antibiotic resistance genes within the gastrointestinal tract of lesser mealworm larvae, Alphitobius diaperinus (Coleoptera: Tenebrionidae)

The frequency of conjugative transfer of antimicrobial resistance plasmids between bacteria within the gastrointestinal tract of lesser mealworm larvae, a prevalent pest in poultry production facilities, was determined. Lesser mealworm larvae were exposed to a negative bacterial control, a donor Salmonella enterica serotype Newport strain, a recipient Escherichia coli, or both donor and recipient to examine horizontal gene transfer of plasmids. Horizontal gene transfer was validated post external disinfection, via a combination of selective culturing, testing of indole production by spot test, characterization of incompatibility plasmids by polymerase chain reaction, and profiling antibiotic susceptibility by a minimum inhibitory concentration (MIC) assay. Transconjugants were produced in all larvae exposed to both donor and recipient bacteria at frequencies comparable to control in vitro filter mating conjugation studies run concurrently. Transconjugants displayed resistance to seven antibiotics in our MIC panel and, when characterized for incompatibility plasmids, were positive for the N replicon and negative for the A/C replicon. The transconjugants did not display resistance to expanded-spectrum cephalosporins, which were associated with the A/C plasmid. This study demonstrates that lesser mealworm larvae, which infest poultry litter, are capable of supporting the horizontal transfer of antibiotic resistance genes and that this exchange can occur within their gastrointestinal tract and between different species of bacteria under laboratory conditions. This information is essential to science-based risk assessments of industrial antibiotic usage and its impact on animal and human health.

Horizontal transfer of the tetracycline resistance gene tetM mediated by pCF10 among Enterococcus faecalis in the house fly (Musca domestica L.) alimentary canal

The house fly (Musca domestica L.) alimentary canal was evaluated for the potential of horizontal transfer of tetM on plasmid pCF10 among Enterococcus faecalis. Two sets of experiments were conducted: (1) house flies without surface sterilization and (2) surface-sterilized flies. Both sets of flies were exposed to E. faecalis OG1RF:pCF10 as donor for 12 h and then E. faecalis OG1SSp as recipient for 1 h. Another group of flies received the recipient first for 12 h followed by exposure to the donor strain for 1 h. House flies were screened daily to determine the donor, recipient, and transconjugant bacterial load for up to 5 days. In addition, the sponge-like mouth parts used for food uptake (labellum) of surface-sterilized house flies were removed and analyzed for donors, recipients, and transconjugants, separately. In both groups of flies (n = 90 flies/group), transfer occurred within 24 h after exposure with a transconjugant/donor rate from 8.6 x 10(-5) to 4.5 x 10(1). Transconjugants were also isolated from the house fly labellum. Our data suggest that the house fly digestive tract provides a suitable environment for horizontal transfer of conjugative plasmids and antibiotic resistance genes among enterococci. Our results emphasize the importance of this insect as a potential vector of antibiotic-resistant bacterial strains.

Beneficial interactions between insects and gut bacteria

Insects are amongst the most successful of animals, both in terms of diversity and in colonizing all ecological niches. Recent studies have highlighted the benefi ciary roles that bacteria play in the success and establishment of insects. By adopting techniques like 16S rRNA sequencing we are now in a position to understand the diversity of bacteria present in insect guts. It has been shown that some of these bacteria, like Wolbachia and Cardinium are involved in manipulating insect populations and distorting their sex ratio. Attempts have been made to culture these bacteria in insect cell lines, as they are recalcitrant to culture under normal microbiological conditions. The diversity of bacteria associated with insects and the functional role played by them in the insect is discussed below.

Gene transfer events and their occurrence in selected environments

Genes encoding virulence determinants are transferred between species in many different environments. In this review we describe gene transfer events to and from different species of bacteria, from bacteria to plants, and from plants to bacteria. Examples of the setting for these transfer events include: the GI tract, the rumen, the oral cavity, and in food matrixes. As a case study, the flux of virulence factors from E.coli O157:H7 is described as an example of gene flow in the environment.

Long-term Hg pollution induced Hg tolerance in the terrestrial isopod Porcellio scaber (Isopoda, Crustacea)

The aim of our work was to assess the pollution-induced community tolerance (PICT) of isopod gut microbiota and pollution-induced isopod population tolerance (PIPT). Animals collected from a chronically Hg polluted and an unpolluted location were exposed for 14 days to 10microg Hg/g dry food under laboratory conditions. The lysosomal membrane stability, hepatopancreas epithelium thickness, feeding activity and animal bacterial gut microbiota composition were determined. The results confirm the hypothesis that the response to short-term Hg exposure differs for animals from the Hg polluted and the unpolluted field locations. The animals and their gut microbiota from the Hg polluted location were less affected by Hg in a short-term feeding experiment than those from the unpolluted environment. We discuss the pollution-induced population tolerance of isopods and their gut microbiota as a measure of effects of long-term environmental pollution. The ecological consequences of such phenomena are also discussed.

Occurrence and antagonistic potential of Stenotrophomonas strains isolated from deep-sea invertebrates

Stenotrophomonas maltophilia is known to be of significance as opportunistic pathogen as well as a source of biocontrol and bioremediation activities. S. maltophilia strains have been isolated from rhizospheres, soil, clinical material, aquatic habitats, but little is known about Stenotrophomonas strains recovered from marine environments. During a survey of the biodiversity of Pseudomonas-like bacteria associated with deep-sea invertebrates six Stenotrophomonas strains were isolated from sponge, sea urchin, and ophiura specimens collected from differing Pacific areas, including the Philippine Sea, the Fiji Sea and the Bering Sea. 16S rRNA gene sequence analysis confirmed an assignment of marine isolates to the genus Stenotrophomonas as it placed four strains into the S. maltophilia CIP 60.77T cluster and two related to the S. rhizophila DSM 14405T. Together with a number of common characteristics typical of S. maltophilia and S. rhizophila marine isolates exhibited differences in pigmentation, a NaCl tolerance, a range of temperatures, which supported their growth, substrate utilization pattern, and antibiotics resistance. Strains displayed hemolytic and remarkable inhibitory activity against a number of fungal cultures and Gram-positive microorganisms, but very weak or none against Candida albicans. This is the first report on isolation, taxonomic characterization and antimicrobial activity of Stenotrophomonas strains isolated from deep-sea invertebrates.

Long-term dynamics of catabolic plasmids introduced to a microbial community in a polluted environment: a mathematical model

The long-term dynamics of mobile plasmids in natural environments are unclear. This is the first study of the long-term dynamics of introduced plasmids with xenobiotic degradation abilities using a mathematical model that describes the horizontal gene transfer (HGT) of plasmids into indigenous bacteria via conjugation. We focussed on negative feedback between the spread of plasmids and their selective advantage, i.e. the severe competition between plasmid-bearing and plasmid-free bacteria resulting from a decrease in xenobiotic concentration caused by the gene expression of plasmids, favoring plasmid-free bacteria. Two types of HGT enhanced the persistence of plasmids and the degradation of the xenobiotic in different conditions: a relatively low rate of 'intergeneric HGT' from introduced to indigenous bacteria and a high rate of 'intraindigenous HGT' from indigenous to indigenous bacteria. In addition, when the indigenous resource supply rate was high and when the cost of bearing plasmids was low, both types of HGT made large contributions to xenobiotic degradation compared to the contribution of vertical transfer via plasmid replication within the introduced host population. Initial conditions were also important; a higher initial density of introduced plasmid-bearing bacteria led to a lower degradation rate over a long time scale.

Benzoic acid-degrading bacteria from the intestinal tract of Macrotermes michaelseni Sjöstedt

The intestinal tracts of termites host a wide variety of microbial symbionts, which have been implicated in degradative processes. In this study, a fungus-cultivating termite, Macrotermes michaelseni was found to harbor 2.2 x 10(6) bacterial cells per ml of gut homogenates capable of degrading benzoic acid. Two benzoic acid degrading bacteria were isolated from the highest dilution of gut homogenates in oxic media with benzoic acid as the sole carbon source. Isolate CBC was related to Stenotrophomonas maltophila LMG 958(T), Xanthomonas campestris DSM 3586(T) and Stenotrophomonas acidaminophila DSM 13117(T) with a sequence similarity of 98.3%, 94.7% and 94.2%, respectively. Isolate CBW was related to Enterobacter aerogenes JCM 1235(T) and Raoultella ornithinolytica ATCC 31898(T) with sequence similarity of 98.4% and 97.8%, respectively. In addition to growing on benzoic acid (up to 9 mM) aerobically, isolate CBW also degraded benzoic acid under anoxic conditions with nitrate as electron acceptor. Isolate CBC did not degrade bezoic acid with nitrate but could degraded resorcinol under oxic conditions.

Bacillus species in the intestine of termites and other soil invertebrates

Soil invertebrates harbour a complex microbial community in their intestinal system. The total number of microbes in the hindgut of soil invertebrates can reach a titre of 10(11) ml(-1). The gut microbes play an indispensable role in the digestion of food and are of ecological importance in the global carbon cycle. The gut microbiota can include a variety of micro-organisms from the three domains Bacteria, Archaea and Eucarya. The bacterial groups from the intestinal systems are mainly affiliated to the proteobacteria, the gram-positive groups Firmicutes and Actinobacteria, the Bacteroides/Flavobacterium branch and the spirochetes. The Archaea are represented by methanogens. The eukaryotic groups consist of protozoa, yeasts and fungi. Intestinal bacteria are involved in the degradation of cellulose, hemicellulose and aromatic compounds as well as nitrogen fixation. They also contribute to the redox status of the gut. Bacilli form a significant portion of the intestinal microbial community of soil invertebrates, especially among cellulose degraders. The diversity and function of bacilli in soil invertebrates will be discussed in this paper.

Field study results on the probability and risk of a horizontal gene transfer from transgenic herbicide-resistant oilseed rape pollen to gut bacteria of bees

Bees are specifically subjected to intimate contacts with transgenic plants due to their feeding activities on pollen. In this study, the probability and ecological risk of a gene transfer from pollen to gut bacteria of bees was investigated with larvae of Apis mellifera (honeybee), Bombus terrestris (bumblebee), and Osmia bicornis (red mason bee), all collected at a flowering transgenic oilseed rape field. The plants were genetically engineered with the pat-gene, conferring resistance against glufosinate (syn. phosphinothricin), a glutamine-synthetase inhibitor in plants and microorganisms. Ninety-six bacterial strains were isolated and characterized by 16S rRNA gene sequencing, revealing that Firmicutes represented 58% of the isolates, Actinobacteria 31%, and Proteobacteria 11%, respectively. Of all isolates, 40% were resistant to 1 mM glufosinate, and 11% even to 10 mM. Resistant phenotypes were found in all phylogenetic groups. None of the resistant phenotypes carried the recombinant pat-gene in its genome. The threshold of detecting gene transfer in this field study was relatively insensitive due to the high background of natural glufosinate resistance. However, the broad occurrence of glufosinate-resistant bacteria from different phylogenetic groups suggests that rare events of horizontal gene transfer will not add significantly to natural bacterial glufosinate resistance.

Resuscitation of Viable But Not Culturable Sinorhizobium meliloti 41 pRP4-luc: Effects of Oxygen and Host Plant

A plasmid-borne, firefly-derived, luciferase gene (luc) was inserted and stably inherited in Sinorhizobium meliloti 41 as a reporter gene. The strain obtained, S. meliloti 41/pRP4-luc, and its parental strain served as a model system for viable but not culturable (VBNC) resuscitation experiments in both in vitro and soil samples. Incubation under oxygen (02) concentrations varying from 1% to atmospheric levels did not result in resuscitation. A demonstration of recovery was attained through exposure to the appropriate concentrations of antibiotics, bacteriostatic chloramphenicol, and bactericidal ampicillin. The resuscitation ratio was 1 recovered VBNC cell in every 10(5) 5-cyano-2,3-di-4-tolyl-tetrazolium chloride (CTC+) bacteria. Although isolated VBNC rhizobia were unable to nodulate Medicago sativa, which apparently did not enhance VBNC reversion, resuscitated bacteria maintained their symbiotic properties. Soil experiments showed that the lack of O2 leads to onset of VBNC status as in liquid microcosm, but the number of recoverable and culturable cells decreased more drastically in soil.

Characterization of a HMT2-like enzyme for sulfide oxidation fromPseudomonas putida

The open reading frame pp0053, which has a high homology with the sequence of mitochondrial sulfide dehydrogenase (HMT2) conferring cadmium tolerance in fission yeast, was amplified from Pseudomonas putida KT2440 and expressed in Escherichia coli JM109(DE3). The isolated and purified PP0053-Hisshowed absorption spectra typical of a flavin adenine dinucleotide (FAD)–binding protein. The PP0053-Hiscatalyzed a transfer of sulfide-sulfur to the thiophilic acceptor, cyanide, which decreased the Kmvalue of the enzyme for sulfide oxidation and elevated the sulfide-dependent quinone reduction. Reaction of the enzyme with cyanide elicited a dose-dependent formation of a charge transfer band, and the FAD-cyanide adduct was supposed to work for a sulfur transfer. The pp0053 deletion from P. putida KT2440 led to activity declines of the intracellular catalase and ubiquinone-H2oxidase. The sulfide-quinone oxidoreductase activity in P. putida KT2440 was attributable to the presence of pp0053, and the activity showed a close relevance to enzymatic activities related to sulfur assimilation.Key words: HMT2-like enzyme, pp0053, Pseudomonas putida, sulfide oxidation.

Endosulfan degradation by a Rhodococcus strain isolated from earthworm gut

A Rhodococcus MTCC 6716 bacterial strain was isolated apparently for the first time from the gut microflora of an Indian earthworm (Metaphire posthuma). Endosulfan was used as a carbon source by the strain and degraded it up to 92.58% within 15 days. Furthermore, the isolated strain of the bacterium did not produce the persistent form of the toxic metabolite endosulfan sulfate. This strain exhibits luxury growth in minimal medium with high concentrations of endosulfan (80 microg mL(-1)). Degradation of the endosulfan occurred simultaneously with bacterial growth and an increase in chloride ion (87.1%) in the growth medium, suggesting nearly complete degradation of the insecticide. This strain is able to tolerate 45 degrees C and retain its degradation potential even under sunlight exposure. Since endosulfan is used worldwide for pest control and its residues have been retained for long periods in soil, water, and agricultural products, the strain isolated by us is valuable for bioremediation of endosulfan-contaminated soil and water.

The phytopathogen Dickeya dadantii (Erwinia chrysanthemi 3937) is a pathogen of the pea aphid

Dickeya dadantii (Erwinia chrysanthemi) is a phytopathogenic bacterium causing soft rot diseases on many crops. The sequencing of its genome identified four genes encoding homologues of the Cyt family of insecticidal toxins from Bacillus thuringiensis, which are not present in the close relative Pectobacterium carotovorum subsp. atrosepticum. The pathogenicity of D. dadantii was tested on the pea aphid Acyrthosiphon pisum, and the bacterium was shown to be highly virulent for this insect, either by septic injury or by oral infection. The lethal inoculum dose was calculated to be as low as 10 ingested bacterial cells. A D. dadantii mutant with the four cytotoxin genes deleted showed a reduced per os virulence for A. pisum, highlighting the potential role of at least one of these genes in pathogenicity. Since only one bacterial pathogen of aphids has been previously described (Erwinia aphidicola), other species from the same bacterial group were tested. The pathogenic trait for aphids was shown to be widespread, albeit variable, within the phytopathogens, with no link to phylogenetic positioning in the Enterobacteriaceae. Previously characterized gut symbionts from thrips (Erwinia/Pantoea group) were also highly pathogenic to the aphid, whereas the potent entomopathogen Photorhabdus luminescens was not. D. dadantii is not a generalist insect pathogen, since it has low pathogenicity for three other insect species (Drosophila melanogaster, Sitophilus oryzae, and Spodoptera littoralis). D. dadantii was one of the most virulent aphid pathogens in our screening, and it was active on most aphid instars, except for the first one, probably due to anatomical filtering. The observed difference in virulence toward apterous and winged aphids may have an ecological impact, and this deserves specific attention in future research.

Studying plasmid horizontal transfer in situ: a critical review

This review deals with the prospective, experimental documentation of horizontal gene transfer (HGT) and its role in real-time, local adaptation. We have focused on plasmids and their function as an accessory and/or adaptive gene pool. Studies of the extent of HGT in natural environments have identified certain hot spots, and many of these involve biofilms. Biofilms are uniquely suited for HGT, as they sustain high bacterial density and metabolic activity, even in the harshest environments. Single-cell detection of donor, recipient and transconjugant bacteria in various natural environments, combined with individual-based mathematical models, has provided a new platform for HGT studies.

Genetically engineered termite gut bacteria (Enterobacter cloacae) deliver and spread foreign genes in termite colonies

Indigenous gut bacteria of the Formosan subterranean termite (Coptotermes formosanus Shiraki, Isoptera: Rhinotermitidae) were used as shuttle systems to deliver, express and spread foreign genes in termite colonies. The gut bacterium Enterobacter cloacae was transformed with a recombinant plasmid (pEGFP) containing genes encoding ampicillin resistance and green fluorescent protein (GFP). In laboratory experiments, termite workers and soldiers from three colonies were fed with filter paper inoculated with transformed bacteria. Transformed bacteria were detected in termite guts by growing the entire gut flora under selective conditions and checking the cultures visually for fluorescence. We demonstrated that (1) transformed bacteria were ingested within a few hours and the GFP gene was expressed in the termite gut; (2) transformed bacteria established a persistent population in the termite gut for up to 11 weeks; (3) transformed bacteria were efficiently transferred throughout a laboratory colony, even when the donor (termites initially fed with transformed bacteria) to recipient (not fed) ratio was low; (4) transformed E. cloacae were transferred into soil; however, they did not accumulate over time and the GFP plasmid was not transferred to other soil bacteria. In the future, transgenic bacteria may be used to shuttle detrimental genes into termite colonies for improved pest control.

Folsomia candida (Collembola): a "standard" soil arthropod

Folsomia candida Willem 1902, a member of the order Collembola (colloquially called springtails), is a common and widespread arthropod that occurs in soils throughout the world. The species is parthenogenetic and is easy to maintain in the laboratory on a diet of granulated dry yeast. F. candida has been used as a "standard" test organism for more than 40 years for estimating the effects of pesticides and environmental pollutants on nontarget soil arthropods. However, it has also been employed as a model for the investigation of numerous other phenomena such as cold tolerance, quality as a prey item, and effects of microarthropod grazing on pathogenic fungi and mycorrhizae of plant roots. In this comprehensive review, aspects of the life history, ecology, and ecotoxicology of F. candida are covered. We focus on the recent literature, especially studies that have examined the effects of soil pollutants on reproduction in F. candida using the protocol published by the International Standards Organization in 1999.

Efficient Transformation of Cellulomonas flavigena by Electroporation and Conjugation with Bacillus thuringiensis

The conjugative self-transmissible plasmid pHT73, harbored in Bacillus thuringiensis var. kurstaki, was demonstrated to be transferred to Cellulomonas flavigena, a cellulolytic bacterium. Both conjugation and transformation procedures yielded resistant colonies; however, chromosomal integration was observed only when bacterial conjugation occurred. The efficiency of conjugation was 10% of recipient strain, which is considered a very efficient process. When the plasmid pHT73 was introduced by transformation, erythromycin-resistant cells contained the plasmid as an episome with no arrangements, as assayed by Southern blot analysis. In contrast, conjugated-resistant cells harbor the plasmid integrated into the chromosome. These data suggest a common mechanism of cell communication between nonrelated bacterial species with similar ecological habitats, and also that both electroporation and conjugation can be used to transform C. flavigena efficiently.

The enhancement of conjugal plasmid pBHR1 transfer between bacteria in the presence of extracellular metabolic products produced by Microcystis aeruginosa

Conjugal plasmid transfer from Escherichia coli S17-1 (pBHR1) to Pseudomonas stutzeri was investigated in the presence of a cyanophyta Microcystis aeruginosa. The plasmid transfer frequency increased with higher densities of M. aeruginosa. The extracellular metabolic products (EMPs) from M. aeruginosa were found to enhance the plasmid transfer between bacteria. Furthermore, the plasmid transfer frequency in medium containing EMPs was significantly higher than that in culture medium with or without glucose. These results suggest that M. aeruginosa enhances conjugal plasmid transfer between bacteria through its EMPs, and that identity of the carbon source is an important factor affecting conjugal plasmid transfer in aquatic environments.

The gut bacteria of insects: nonpathogenic interactions

The diversity of the Insecta is reflected in the large and varied microbial communities inhabiting the gut. Studies, particularly with termites and cockroaches, have focused on the nutritional contributions of gut bacteria in insects living on suboptimal diets. The indigenous gut bacteria, however, also play a role in withstanding the colonization of the gut by non-indigenous species including pathogens. Gut bacterial consortia adapt by the transfer of plasmids and transconjugation between bacterial strains, and some insect species provide ideal conditions for bacterial conjugation, which suggests that the gut is a "hot spot" for gene transfer. Genomic analysis provides new avenues for the study of the gut microbial community and will reveal the molecular foundations of the relationships between the insect and its microbiome. In this review the intestinal bacteria is discussed in the context of developing our understanding of symbiotic relationships, of multitrophic interactions between insects and plant or animal host, and in developing new strategies for controlling insect pests.

Detection and phylogenetic analysis of Wolbachia in Collembola

Wolbachia are obligatory, cytoplasmatically inherited alpha-Proteobacteria which are known for infecting the reproductive tissues of many arthropods. Their prevalence in the large group of Collembola, however, is not known, except for PCR detection in the parthenogenetically reproducing species Folsomia candida (Order: Entomobryomorpha; Family: Isotomidae). In this study, fluorescence in situ hybridization on microscopic sections of F. candida specimens indicated that Wolbachia-related bacteria were restricted to tissues of the ovary and brain. PCR with primers designed to detect 16S rRNA genes of Wolbachia were positive with specimens from all of five geographically independent F. candida breeding stocks and with three parthenogenetic species from another order (Poduromorpha; Family Tullbergiidae), i.e. Mesaphorura italica, M. macrochaeta and Paratullbergia callipygos. In contrast, negative results were obtained with the two sexually reproducing species, Isotoma viridis (Isotomidae) and Protaphorura fimata (Poduromorpha; Onychiuridae). The ftsZ gene of Wolbachia could be PCR-amplified from all Wolbachia-positive hosts with the exception of M. macrochaeta. The phylogenetic distances of the ftsZ and 16S rRNA gene sequences reflected the phylogenetic distances of the host organisms but the sequences of Wolbachia were relatively closely related, indicating that Wolbachia infections took place after the Collembola had diversified. Our study confirms a monophyletic branch (supergroup E) of Collembola colonizing Wolbachia and indicates that this group is a sister group of supergroup A, the latter harbouring a high diversity of host organisms within the group of insects.