Characteristics of <Emphasis Type="Italic">Pseudomonas aurantiaca</Emphasis> DNA supramolecular complexes at various developmental stages

Differences in viscoelasticity (η) and molecular mass (M) values, as well as in the fatty acid profile of lipids in DNA supramolecular complexes (SC), isolated from Pseudomonas aurantiaca cultures at the exponential and stationary growth phases, were established for the first time. Typical characteristics of DNA SC from actively growing cells were the following: η = 315 ± 15 dl/g, M_DNA = 39 × 10⁶ Da, C_16:0 > C_18:0 > C_18:1 present as basic fatty acids (FA) in a pool of loosely DNA-bound lipids; the tightly DNA-bound lipid fraction consisted of only two acids C_18:0 > C_16:0. Significantly higher values of viscoelasticity η = 779 ± 8 dl/g and M_DNA = 198 × 10⁶ Da were observed for DNA SC of the stationary phase cells; one more FA, C_14:0, was detected in the loosely bound lipid fraction, while lipids tightly bound to DNA contained mainly C_16:0 > C_18:1 > C_18:0 > C_14:0 FA. The content of saturated FA in the DNA-bound lipids in the stationary phase cells was twice as high than in the exponential phase cells. The fraction of tightly bound lipids from the stationary phase cells contained nine times more unsaturated fatty acids than the fraction from proliferating cells. These differences in FA composition of DNA-bound lipids demonstrate the importance of lipids for the structural organization and functioning of genomic DNA during bacterial culture development.     

Structural and physiological diversity among cystlike resting cells of bacteria of the genus <Emphasis Type="Italic">Pseudomonas</Emphasis>

Cystlike resting cells (CRC) of non-spore-forming gram-negative bacteria of the genus Pseudomonas, P. aurantiaca and P. fluorescens, were obtained and characterized for the first time; their physiological and morphological diversity was demonstrated. The following properties were common for all the revealed types of CRC as dormant forms: (1) long-term (up to 6 months or longer) maintenance of viability in the absence of culture growth and cell respiration; (2) absence of an experimentally detectable level of metabolism; (3) higher resistance to damage and autolysis under the action of provoking factors than in metabolically active vegetative cells; and (4) specific features of ultrastructural organization absent in vegetative cells: thickened and lamellar envelopes, clumpy structure of the cytoplasm, and condensed DNA in nucleoid. The differences in various types of CRC concern the thickness and lamellar structure of cell envelopes, as well as the presence and thickness of the capsular layer. In particular, forms ultrastructurally similar to typical bacterial cysts were revealed in pseudomonad populations growing on soil agar. Physiological diversity was revealed in different levels of viability preservation and thermal resistance in various types of CRC and depended on the conditions of their formation. The optimal conditions and procedures for obtaining P. aurantiaca and P. fluorescens CRC that retain the ability to form colonies on standard nutrient media are as follows: (1) a twofold decrease of nitrogen content in the growth medium; (2) an increased level of anabiosis autoinducer (C₁₂-AHB, 10^?4 M) in stationary cultures; (3) transfer of the cells from stationary cultures to a starvation medium with silica; (4) cultivation in soil extract; and (5) development of cultures on soil agar. The CRC from the cultures grown in soil extract or starvation medium with silica proved to be resistant to heat treatment (60°C, 5 min). In the CRC formed in nitrogen-limited media, the degree of heat resistance increased at longer incubation (1.5 to 6 months). CRCs on soil agar surface were resistant to desiccation. The ultrastructure of the morphologically varied types of P. aurantiaca CRC formed under simulated natural conditions is described for the first time. The data on the intraspecies diversity of pseudomonad dormant forms contribute to the concept of plasticity of the life style and adaptive reactions that ensure survival of these bacteria in unfavorable environmental conditions.     

Effect of alkylhydroxybenzenes, microbial anabiosis inducers, on the structural organization of Pseudomonas aurantiaca DNA and on phenotypic dissociation induction

We revealed a relationship between alkylhydroxybenzene (AHB)-induced changes in the structural organization of supramolecular complexes (SC) of the DNA of Pseudomonas auraniaca and the phenotypic dissociation of this bacterium. The addition of 0.1-0.3 mM hexylresorcinol (C6-AHB), a chemical analogue of microbial anabiosis autoinducers, caused the formation of cystlike refractile cells (CRC) in these gram-negative, nonsporulating bacteria. Inoculating pseudomonad CRC on solid nutrient media resulted in phenotypic dissociation of the microbial population that yielded several variants with different colony structure and morphology. This manifested itself in the conversion of the original S-colony-forming phenotype into the R form and in the formation of less pigmented colonies. These transitions were possibly linked to AHB-induced structural changes in the DNA. In vitro studies revealed that AHB could interact with DNA SC, resulting in their structural modification that manifested itself in changes in their elastoviscosity. DNA supramolecular complexes isolated from proliferating, stationary-phase, and anabiotic P. aurantiaca cells differed in their elastoviscosity and capacity to interact with AHB homologues with different hydrophobicity, such as hexylresorcinol and methylresorcinol (C1-AHB). The DNA SC from actively proliferating cells were characterized by smaller elastoviscosity compared with those from stationary-phase and anabiotic cells, due to the difference in the DNA superspiralization degree and the physiological age of the bacteria involved. C6-AHB produced a pronounced relaxing effect on the DNA SC from exponential-phase P. aurantiaca cells. The less hydrophobic C1-AHB produced a similar effect on the DNA SC from stationary-phase cells. The curve of the dose-effect dependence of C6-AHB had a breaking point within the submillimolar (10(-4) M) concentration range. These concentrations induce the formation of cystlike anabiotic pseudomonad cells that are characterized by an unstable genotype and dissociate into distinct variants upon inoculation on solid media.     

The role of alkylhydroxybenzenes in the adaptation of <Emphasis Type="Italic">Micrococcus luteus</Emphasis> to heat shock

The response of the gram-positive bacterium micrococcus luteus to heat shock (4°C, 15 min) and the adaptogenic activity of alkylhydroxybenzenes (AHBs), which are extracellular growth-regulating substances of these bacteria, were studied. The perception of stress and the postshock behavior of M. luteus cells proved to depend on the growth phase and medium. The magnitude of the stress response was more pronounced in cultures grown on synthetic medium than in cultures grown on rich medium (nutrient broth). During exponential or linear growth, the cells were more sensitive to the temperature effect than during decelerated growth. In linearly growing m. luteus cultures, the amount of total intra- and extracellular alkylhydroxybenzenes, the anabiosis inducers, increased in response to heat shock. AHB redistribution between cells and culture liquid occurred in the course of stress and after stress. In micrococci exposed to heat shock, an increase in the AHB concentration both in cells and in culture liquid is likely a defense reaction of stress resistance. This conclusion was confirmed in experiments with the addition 30 min before the heat shock of a chemical analogue of the anabiosis inducer, C₇-AHB (12 mM), which protected M. luteus cells so that their intense growth was observed after shock without any lag. The protective effect of AHBs is a result of their ability to form complexes with enzyme macromolecules and stabilize them. The data obtained extend the knowledge of the stress-protective functions of low-molecular-weight autoregulators and of the role of intercellular communications in the stress response of bacterial cultures.Translated from Mikrobiologiya, Vol. 74, No. 1, 2005, pp. 26–33.Original Russian Text Copyright © 2005 by Stepanenko, Mulyukin, Kozlova, Nikolaev, El-Registan.     

Detection of <Emphasis Type="Italic">Candida</Emphasis><Emphasis Type="Italic">dubliniensis</Emphasis> in Venezuela

Over the past decades there has been a significant increase in fungal infections caused by Candida species, and continues to be common in immunocompromised individuals infected with the human immunodeficiency virus (HIV). Although Candida albicans remains the fungal species most frequently isolated as an opportunistic oral pathogen, other non-albicans are often identified in this cohort of patients, including C. dubliniensis. This yeast is closely related to and shares many phenotypic characteristics with C. albicans. Colonies of these two species appear morphologically identical when not grown on special media. The shared phenotypic characteristics of C. dubliniensis and C. albicans suggest that many C. dubliniensis isolates may have been misidentified as C. albicans in the past. The present studies aim is to recover and identify C. dubliniensis, and presumptive clinical C. albicans, from the oral cavities of HIV-seropositive individuals, comparing conventional media to obtain a simple, low-cost and reliable identification system for C. dubliniensis. A total of 16 isolates (3,98%) had been obtained from 402 HIV infected individuals with recurrent oropharyngitis and were identified as C. dubliniensis. Out of these C. dubliniensis isolates 19% were resistant, with MICs above 64 μg/ml to fluconazole. This constitutes, to the authors knowledge the first recovery of this organism in Venezuela.     

DNA elements modulating the <Emphasis Type="Italic">KARS12</Emphasis> chromosomal replicator in <Emphasis Type="Italic">Kluyveromyces lactis</Emphasis>

Eukaryotic chromosomal DNA replication is initiated by a highly conserved set of proteins that interact with cis-acting elements on chromosomes called replicators. Despite the conservation of replication initiation proteins, replicator sequences show little similarity from species to species in the small number of organisms that have been examined. Examination of replicators in other species is likely to reveal common features of replicators. We have examined a Kluyeromyces lactis replicator, KARS12, that functions as origin of DNA replication on plasmids and in the chromosome. It contains a 50-bp region with similarity to two other K. lactis replicators, KARS101 and the pKD1 replication origin. Replacement of the 50-bp sequence with an EcoRI site completely abrogated the ability of KARS12 to support plasmid and chromosomal DNA replication origin activity, demonstrating this sequence is a common feature of K. lactis replicators and is essential for function, possibly as the initiator protein binding site. Additional sequences up to 1 kb in length are required for efficient KARS12 function. Within these sequences are a binding site for a global regulator, Abf1p, and a region of bent DNA, both of which contribute to the activity of KARS12. These elements may facilitate protein binding, protein/protein interaction and/or nucleosome positioning as has been proposed for other eukaryotic origins of DNA replication.     

Improvement of growth,under field conditions,of wheat inoculated with <Emphasis Type="Italic">Pseudomonas chlororaphis</Emphasis> subsp.<Emphasis Type="Italic"> aurantiaca</Emphasis> SR1

Effects of inoculation of wheat (Triticum aestivum L.) with the rhizobacterium Pseudomonas chlororaphis subsp. aurantiaca strain SR1 (termed SR1) were studied at an experimental field site in Río Cuarto, Argentina. Treatments involved SR1 inoculation with or without nitrogen/phosphorus fertilization. Inoculation produced a significant increase in plant height and root length in early growth stages. Inoculation plus fertilization with 40 kg ha⁻¹ urea/30 kg ha⁻¹ diamonic phosphate (“50% dose”) gave a yield increase of 636 kg ha⁻¹ relative to control, and an increase of 472 kg ha⁻¹ relative to fertilization with 80 kg ha⁻¹ urea/60 kg ha⁻¹ phosphate without inoculation. SR1 inoculation without fertilization, compared to control, produced increases of 6% in weight of 1,000 grains, 13% in number of spikes per plant, and 30% in number of grains per spike. Inoculation plus 50% dose fertilization also improved these parameters. Results of the study indicate that inoculation of wheat with SR1 improves various growth and yield parameters, and allows reduced dosage of nitrogen/phosphorus fertilizers in the field.     

Extracellular DNA and Type IV pili mediate surface attachment by <Emphasis Type="Italic">Acidovorax</Emphasis><Emphasis Type="Italic">temperans</Emphasis>

Extracellular DNA can play a structural role in the microbial environment. Here evidence is presented that an environmental isolate of Acidovorax temperans utilises extracellular DNA for intercellular and cell-surface attachment and that Type IV pili and electrostatic interactions play a role in this interaction. Preliminary attempts to isolate and purify extracellular polysaccharides from A. temperans strain CB2 yielded significant amounts of DNA raising the question of whether this molecule was present as a structural component in the extracellular matrix. The role of DNA in attachment was indicated by experiments in which the addition of DNase to liquid medium inhibited the attachment of Acidovorax to glass wool. A Tn5 insertional mutant, lacking Type IV pili, was unable to initiate attachment. Addition of DNase caused rapid detachment of bound cells, but no detachment occurred when proteinase, RNase or inactivated DNase were used. Addition of MgCl₂ also caused significant detachment, supporting the possible mechanistic role of electrostatic interactions in the attachment process. Although attachment was apparent in early to mid-log phase growth, surprisingly DNA was not detected in the culture supernatant until late stationary phase and coincided with an appreciable loss of cell viability. This suggests that during log-phase growth attachment is mediated by eDNA that is released in low quantities and/or is highly localised within the extracellular matrix and also that stationary phase DNA release through widespread cell lysis may be a separate and unrelated event.     

<Emphasis Type="Italic">Sporidiobolus johnsonii</Emphasis> and <Emphasis Type="Italic">Sporidiobolus salmonicolor</Emphasis> revisited

The relationship between Sporidiobolus johnsonii and S. salmonicolor was investigated using rDNA sequence data. Two statistically well-supported clades were obtained. One clade included the type strain of S. johnsonii and the other included the type strain of S. salmonicolor. However, some mating strains of S. salmonicolor were found in the S. johnsonii group. These strains belonged to mating type A2 and were sexually compatible with mating type A1 strains from the S. salmonicolor group. DNA–DNA reassociation values were high within each clade and moderate between the two clades. In the re-investigation of teliospore germination, we observed that the basidia of S. salmonicolor were two-celled. In S. johnsonii, basidia were not formed and teliospore germination resulted in direct formation of yeast cells. We hypothesize that the S. johnsonii clade is becoming genetically isolated from the S. salmonicolor group and that a speciation process is presently going on. We suspect that the observed sexual compatibility between strains of the S. johnsonii and S. salmonicolor groups and the possible genetic flow between the two species has little biological relevance because distinct phenotypes have been fixed in the two taxa and intermediate (hybrid) sequences for LSU and ITS rDNAs have not been detected. An erratum to this article can be found at     

<Emphasis Type="Italic">AtTBP2</Emphasis> and <Emphasis Type="Italic">AtTRP2</Emphasis> in <Emphasis Type="Italic">Arabidopsis</Emphasis> encode proteins that bind plant telomeric DNA and induce DNA bending in vitro

Telomeric DNA-binding proteins (TBPs) are crucial components that regulate the structure and function of eukaryotic telomeres and are evolutionarily conserved. We have identified two homologues of AtTBP1 (for Arabidopsis thaliana telomeric DNA binding protein 1), designated as AtTBP2 and AtTRP2, which encode proteins that specifically bind to the telomeric DNA of this plant. These proteins show extensive homology with other known plant TBPs. The isolated C-terminal segments of these proteins were capable of sequence-specific binding to duplex telomeric plant DNA in vitro. DNA bending assays using the Arabidopsis TBPs revealed that AtTBP1 and AtTBP2 have DNA-bending abilities comparable to that of the human homologue hTRF1, and higher than those of AtTRP1 and AtTRP2.     

Mitochondrial <Emphasis Type="Italic">cox</Emphasis>1 and plastid <Emphasis Type="Italic">rbc</Emphasis>L genes of <Emphasis Type="Italic">Gracilaria vermiculophylla</Emphasis> (Gracilariaceae,Rhodophyta)

The mitochondrial cytochrome c oxidase subunit I gene sequence was recently developed for DNA barcoding of red algal species. We determined the 1245 base pairs of the gene from 27 taxa of an agar-producing species, Gracilaria vermiculophylla, and putative relatives and compared the results with rbcL data from the same species. A total of 392 positions (31.5%) were variable, 282 positions (22.6%) were parsimoniously informative, and average sequence divergence was 13% in an ingroup. Within G. vermiculophylla, pairwise divergence of the gene was variable up to 11 bp (0.9%). Seven recognized haplotypes of cox1 tended to be geographically related. In the aligned 1386 bp of rbcL, three haplotypes were recognized. These results suggest that cox1 is a valuable molecular marker within species and will be very useful in haplotype analyses.     

Revision of the <Emphasis Type="Italic">Serrulati</Emphasis> species of <Emphasis Type="Italic">Penstemon</Emphasis> section <Emphasis Type="Italic">Saccanthera</Emphasis> subsection <Emphasis Type="Italic">Serrulati</Emphasis>

A revision of Penstemon sect. Saccanthera subsect. Serrulati includes a new species (P. salmonensis), a new variety (P. triphyllus var. infernalis), and the elevation of a subspecies to species (P. curtiflorus), bringing the total number of species to eight, which are keyed and described, complete with nomenclature and type citations.     

Assembly of the <Emphasis Type="Italic">Tc1</Emphasis> and <Emphasis Type="Italic">mariner</Emphasis> transposition initiation complexes depends on the origins of their transposase DNA binding domains

In this review, we focus on the assembly of DNA/protein complexes that trigger transposition in eukaryotic members of the IS630–Tc1–mariner (ITm) super-family, the Tc1- and mariner-like elements (TLEs and MLEs). Elements belonging to this super-family encode transposases with DNA binding domains of different origins, and recent data indicate that the chimerization of functional domains has been an important evolutionary aspect in the generation of new transposons within the ITm super-family. These data also reveal that the inverted terminal repeats (ITRs) at the ends of transposons contain three kinds of motif within their sequences. The first two are well known and correspond to the cleavage site on the outer ITR extremities, and the transposase DNA binding site. The organization of ITRs and of the transposase DNA binding domains implies that differing pathways are used by MLEs and TLEs to regulate transposition initiation. These differences imply that the ways ITRs are recognized also differ leading to the formation of differently organized synaptic complexes. The third kind of motif is the transposition enhancers, which have been found in almost all the functional MLEs and TLEs analyzed to date. Finally, in vitro and in vivo assays of various elements all suggest that the transposition initiation complex is not formed randomly, but involves a mechanism of oriented transposon scanning. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . An erratum to this article can be found at     

<Emphasis Type="Italic">In vitro</Emphasis> root induction in weedy <Emphasis Type="Italic">amaranthus</Emphasis> species to obtain mitotic chromosomes

Summary Mitotic chromosome analysis has proven to be an important tool in monitoring the potential for genetic exchange among related plant species. One major obstacle to using mitotic chromosome analysis in any species is obtaining large numbers of clear, well-spread metaphase chromosomes necessary to perform cytological techniques such as chromosome banding and fluorescent in situ hybridization. The ability to obtain good chromosome spreads is in part determined by the number and morphology of the roots, which contain the metaphase tissue. Many Amaranthus species produce very thin, delicate roots. The technique used in the process described herein provides for much more substantial roots, allowing for higher probability of obtaining well-spread metaphase chromosomes. Seeds were planted in a soilless mixture, and then cuttings and leaves were taken from the plants. The cuttings were sterilized and placed in Murashige and Skoog (MS) media, while leaf tissue was analyzed by flow cytometry, both pre-and post-propagation, to obtain DNA contents. No changes in DNA content were observed. The in vitro procedure produced significantly larger roots than were produced in soilless mix. Furthermore, all of the in vitro roots observed had 32 chromosomes of normal morphology. In vitro root propagation allowed large numbers of roots to be obtained from a single plant, thereby resulting in increased probability of obtaining cells with metaphase chromosomes that reflected the original plants' chromosome numbers and therefore may be used for molecular cytogenetic analysis.     

Effect of <Emphasis Type="Italic">cra</Emphasis> gene knockout together with <Emphasis Type="Italic">edd</Emphasis> and <Emphasis Type="Italic">iclR</Emphasis> genes knockout on the metabolism in <Emphasis Type="Italic">Escherichia coli</Emphasis>

To elucidate the physiological adaptation of Escherichia coli due to cra gene knockout, a total of 3,911 gene expressions were investigated by DNA microarray for continuous culture. About 50 genes were differentially regulated for the cra mutant. TCA cycle and glyoxylate shunt were down-regulated, while pentose phosphate (PP) pathway and Entner Doudoroff (ED) pathway were up-regulated in the cra mutant. The glucose uptake rate and the acetate production rate were increased with less acetate consumption for the cra mutant. To identify the genes controlled by Cra protein, the Cra recognition weight matrix from foot-printing data was developed and used to scan the whole genome. Several new Cra-binding sites were found, and some of the result was consistent with the DNA microarray data. The ED pathway was active in the cra mutant; we constructed cra.edd double genes knockout mutant to block this pathway, where the acetate overflowed due to the down-regulation of aceA,B and icd gene expressions. Then we further constructed cra.edd.iclR triple genes knockout mutant to direct the carbon flow through the glyoxylate pathway. The cra.edd.iclR mutant showed the least acetate production, resulting in the highest cell yield together with the activation of the glycolysis pathway, but the glucose consumption rate could not be improved. Dayanidhi Sarkar and Khandaker Al Zaid Siddiquee have contributed equally.     

The tyrosine <Emphasis Type="Italic">O</Emphasis>-prenyltransferase SirD catalyzes <Emphasis Type="Italic">O</Emphasis>-, <Emphasis Type="Italic">N</Emphasis>-, and <Emphasis Type="Italic">C</Emphasis>-prenylations

Recently, the prenyltransferase SirD was found to be responsible for the O-prenylation of tyrosine in the biosynthesis of sirodesmin PL in Leptosphaeria maculans. In this study, the behavior of SirD towards phenylalanine/tyrosine and tryptophan derivatives was investigated. Product formation has been observed with 12 of 19 phenylalanine/tyrosine derivatives. It was shown that the alanine structure attached to the benzene ring and an electron donor, e.g., OH or NH₂, at its para-position are essential for the enzyme activity. Modifications were possible both at the side chain and the benzene ring. Enzyme products from seven phenylalanine/tyrosine derivatives were isolated and characterized by MS and NMR analyses including HSQC and HMBC and proven to be O- or N-prenylated derivatives at position C4 of the benzene rings. K _M values of six selected derivatives were found in the range of 0.10–0.68 mM. Catalytic efficiencies (K _cat/K _M ) were determined in the range of 430–1,110 s⁻¹·M⁻¹ with l-tyrosine as the best substrate. In addition, 7 of 14 tested tryptophan analogs were also accepted by SirD and converted to C7-prenylated derivatives, which was confirmed by comparison with products obtained from enzyme assays using a 7-dimethylallyltryptophan synthase 7-DMATS from Aspergillus fumigatus.     

Novel DNA glycosylases from <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis>

Oxidized bases are removed from DNA of Escherichia coli by enzymes formamidopyrimidine DNA glycosylase (Eco-Fpg) and endonuclease VIII (Eco-Nei) of the same structural family Fpg/Nei. New homologs of these enzymes not characterized earlier have been found in genomes of Actinobacteria. We have cloned and expressed two paralogs (Mtu-Nei2 and Mtu-Fpg2) from 36KAZ and KHA94 isolates of Mycobacterium tuberculosis and studied their ability to participate in DNA repair. Under heterologous expression in E. coli, Mtu-Nei2 decreased the rate of spontaneous mutagenesis in the rpoB gene, whereas Mtu-Fpg2 moderately increased it, possibly due to absence of residues crucially important for catalysis in this protein. Mtu-Nei2 was highly active toward double-stranded DNA substrates containing dihydrouracil residues and apurine-apyrimidine sites and was less efficient in cleavage of substrates containing 8-oxoguanine and uracil residues. These lesions, as well as 8-oxoadenine residues, were also recognized and removed by the enzyme from single-stranded DNA. Fpg and Nei homologs from M. tuberculosis can play an important role in protection of bacteria against genotoxic stress caused by oxidative burst in macrophages.     

New combinations and typifications in <Emphasis Type="Italic">Bistorta</Emphasis>, <Emphasis Type="Italic">Persicaria</Emphasis>, <Emphasis Type="Italic">Polygonum,</Emphasis> and <Emphasis Type="Italic">Rumex</Emphasis> (Polygonaceae)

New combinations are proposed in anticipation of the Polygonaceae treatment in the forthcoming volume of Intermountain Flora: Polygonum kelloggii var. esotericum, P. kelloggii var. watsonii , Rumex densiflorus var. pycnanthus , R. salicifolius var. utahensis, and R. occidentalis var. tomentellus. Typifications are proposed to facilitate ongoing studies in Polygonaceae and to maintain current usage.     

<Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> inhibits <Emphasis Type="Italic">in-vitro Candida</Emphasis> biofilm development

Background  

Elucidation of the communal behavior of microbes in mixed species biofilms may have a major impact on understanding infectious diseases and for the therapeutics. Although, the structure and the properties of monospecies biofilms and their role in disease have been extensively studied during the last decade, the interactions within mixed biofilms consisting of bacteria and fungi such as Candida spp. have not been illustrated in depth. Hence, the aim of this study was to evaluate the interspecies interactions of Pseudomonas aeruginosa and six different species of Candida comprising C. albicans, C. glabrata, C. krusei, C. tropicalis, C. parapsilosis, and C. dubliniensis in dual species biofilm development.     

The <Emphasis Type="Italic">Caenorhabditis</Emphasis><Emphasis Type="Italic">briggsae</Emphasis> genome contains active <Emphasis Type="Italic">CbmaT1</Emphasis> and <Emphasis Type="Italic">Tcb1</Emphasis> transposons

The maT clade of transposons is a group of transposable elements intermediate in sequence and predicted protein structure to mariner and Tc transposons, with a distribution thus far limited to a few invertebrate species. We present evidence, based on searches of publicly available databases, that the nematode Caenorhabditis briggsae has several maT-like transposons, which we have designated as CbmaT elements, dispersed throughout its genome. We also describe two additional transposon sequences that probably share their evolutionary history with the CbmaT transposons. One resembles a fold back variant of a CbmaT element, with long (380-bp) inverted terminal repeats (ITRs) that show a high degree (71%) of identity to CbmaT1. The other, which shares only the 26-bp ITR sequences with one of the CbmaT variants, is present in eight nearly identical copies, but does not have a transposase gene and may therefore be cross mobilised by a CbmaT transposase. Using PCR-based mobility assays, we show that CbmaT1 transposons are capable of excising from the C. briggsae genome. CbmaT1 excised approximately 500 times less frequently than Tcb1 in the reference strain AF16, but both CbmaT1 and Tcb1 excised at extremely high frequencies in the HK105 strain. The HK105 strain also exhibited a high frequency of spontaneous induction of unc-22 mutants, suggesting that it may be a mutator strain of C. briggsae.