Mechanism Of Gene Transfer Research Articles

Regulation of Virulence Gene Expression in Bacteria: A Review

Bacterial diseases are the leading cause of death worldwide through the involvement of virulence determinants. Virulence genes encode virulence factors which are essential for pathogenesis and infectious disease development in bacteria. The virulence factor concept helps for further investigations in the fields of microbial pathogenesis. The objective of this paper is to review regulation of virulence gene expression in bacteria. Virulence genes can be acquired via spontaneous mutations or through horizontal gene transfer mechanisms. Bacteria sense and respond to environmental stimuli in the host during infection. Successful host infection can be possible by coordinated expression of multitude of virulence genes. They adapt in the host by modulating its gene expression. Pathogenic bacteria possess many regulatory networks that control the production of virulence factors which enable the bacteria to survive and proliferate in the host. The most common forms of regulation of genome expression are by involvement of transcription factors, post-transcriptional modifications, ribo-regulation, environmental flux sensing, stress response and biofilm formation through quorum sensing. Virulence gene expression is carefully controlled to ensure correct spatiotemporal production of virulence factors. Regulation of virulence gene expression is very complex and influenced by environmental factors. Major regulatory control mechanisms used by pathogenic bacteria are alternative sigma factors and the two component regulatory systems. They do not always express virulence factors because it is energetically costly and reduces bacterial fitness. Therefore, they need to regulate their virulence properly in order to maximize their fitness and it is a key invasion strategy of pathogens. Keywords: Bacteria, Expression, Regulation, Virulence gene DOI: 10.7176/JBAH/11-3-02 Publication date: February 28 th 2021

Antibiogram status of Commensal Strains involved in Multidrug Resistance recovered from famous street foods of Karachi: A threat for public health.

Background: Antimicrobial resistance is, as of now, the quintessential issue these days and commensal microorganisms are contributing their part efficiently in disseminating resistance. Thus, this investigation aimed to determine the antibiogram pattern of bacteria recovered from street vended foods in Karachi city.
 Methodology: Kirby Bauer's disc diffusion technique was done to check the sensitivity pattern of foodborne bacteria towards 11 standard antibiotics with a range of (11 - 40 mm) inhibition zone. 
 Results: Nearly all the tested food isolates showed resistance towards oxacillin and amoxicillin. Strains of S. faecalis demonstrated 100 % resistance against gentamicin, chloramphenicol, oxacillin, tobramycin, and streptomycin. Ready-to-eat food contaminated with a high bacterial count is an important matter of concern.
 Conclusion: Commensal bacteria are responsible for several foodborne sicknesses and are involved in the mechanism of lateral gene transfer. Hence, the exploitation of drugs and violation of acceptable sanitation standards and good hygiene practices must be restricted to restrain the antimicrobial drug resistance and provide good quality food that fulfills the requirements of consumers' wellbeing.

Beyond the pan-genome: current perspectives on the functional and practical outcomes of the distributed genome hypothesis.

The principle of monoclonality with regard to bacterial infections was considered immutable prior to 30 years ago. This view, espoused by Koch for acute infections, has proven inadequate regarding chronic infections as persistence requires multiple forms of heterogeneity among the bacterial population. This understanding of bacterial plurality emerged from a synthesis of what-were-then novel technologies in molecular biology and imaging science. These technologies demonstrated that bacteria have complex life cycles, polymicrobial ecologies, and evolve in situ via the horizontal exchange of genic characters. Thus, there is an ongoing generation of diversity during infection that results in far more highly complex microbial communities than previously envisioned. This perspective is based on the fundamental tenet that the bacteria within an infecting population display genotypic diversity, including gene possession differences, which result from horizontal gene transfer mechanisms including transformation, conjugation, and transduction. This understanding is embodied in the concepts of the supragenome/pan-genome and the distributed genome hypothesis (DGH). These paradigms have fostered multiple researches in diverse areas of bacterial ecology including host–bacterial interactions covering the gamut of symbiotic relationships including mutualism, commensalism, and parasitism. With regard to the human host, within each of these symbiotic relationships all bacterial species possess attributes that contribute to colonization and persistence; those species/strains that are pathogenic also encode traits for invasion and metastases. Herein we provide an update on our understanding of bacterial plurality and discuss potential applications in diagnostics, therapeutics, and vaccinology based on perspectives provided by the DGH with regard to the evolution of pathogenicity.

Antibiotic and antibiotic-resistant gene loads in swine slurries and their digestates: Implications for their use as fertilizers in agriculture

The spread of antibiotic resistance in bacteria is a matter of global concern, and the identification of possible sources of the associated genetic elements (antibiotic resistance genes -ARGs-, components of the horizontal gene transfer mechanism), is becoming an urgent need. While the transmission of ARGs in medical settings have been adequately characterized, ARG propagation in agroecosystems remains insufficiently studied. Particularly crucial is the determination of potential risks associated to the use of swine slurries and related products as component of organic fertilizers, an increasingly used farming practice. We determined ARGs and antibiotic loads analysed from swine slurries and digestates from eight farms from Catalonia (NE Spain), and compared the results with their microbiome composition. Both ARGs and antibiotic were conspicuous in farm organic wastes, and the levels of some antibiotics exceeded currently accepted minimum inhibitory concentrations. Particularly, the presence of high loads of fluoroquinolones was directly correlated to the prevalence of the related qnrS1 ARG in the slurry. We also found evidence that ARG loads were directly correlated to the prevalence of determined bacterial taxa (Actinobacteria, Proteobacteria, Spirochaeta), a parameter that could be potentially modulated by the processing of the raw slurry prior to their use as fertilizer.

Microbial communities and gene contributions in smokeless tobacco products.

Smokeless tobacco products (STP) contain bacteria, mold, and fungi due to exposure from surrounding environments and tobacco processing. This has been a cause for concern since the presence of microorganisms has been linked to the formation of highly carcinogenic tobacco-specific nitrosamines. These communities have also been reported to produce toxins and other pro-inflammatory molecules that can cause mouth lesions and elicit inflammatory responses in STP users. Moreover, microbial species in these products could transfer to the mouth and gastrointestinal tract, potentially altering the established respective microbiotas of the consumer. Here, we present the first metagenomic analysis of select smokeless tobacco products, specifically US domestic moist and dry snuff. Bacterial, eukaryotic, and viral species were found in all tobacco products where 68% of the total species was comprised of Bacteria with 3 dominant phyla but also included 32% Eukarya and 1% share abundance for Archaea and Viruses. Furthermore, 693,318 genes were found to be present and included nitrate and nitrite reduction and transport enzymes, antibiotic resistance genes associated with resistance to vancomycin, β-lactamases, their derivatives, and other antibiotics, as well as genes encoding multi-drug transporters and efflux pumps. Additional analyses showed the presence of endo- and exotoxin genes in addition to other molecules associated with inflammatory responses. Our results present a novel aspect of the smokeless tobacco microbiome and provide a better understanding of these products' microbiology. KEY POINTS: • The findings presented will help understand microbial contributions to overall STP chemistries. • Gene function categorization reveals harmful constituents outside canonical forms. • Pathway genes for TSNA precursor activity may occur at early stages of production. • Bacteria in STPs carry antibiotic resistance genes and gene transfer mechanisms.

Staphylococcal Protein A (spa) Locus Is a Hot Spot for Recombination and Horizontal Gene Transfer in Staphylococcus pseudintermedius.

Staphylococcus pseudintermedius is a major canine pathogen but also occasionally colonizes and infects humans. Multidrug-resistant methicillin-resistant S. pseudintermedius (MDR MRSP) strains have emerged globally, making treatment and control of this pathogen challenging. Sequence type 71 (ST71), ST68, and ST45 are the most widespread and successful MDR MRSP clones. The potential genetic factors underlying the clonal success of these and other predominant clones remain unknown. Characterization of the pangenome, lineage-associated accessory genes, and genes acquired through horizontal gene transfer from other bacteria is important for identifying such factors. Here, we analyzed genome sequence data from 622 S. pseudintermedius isolates to investigate the evolution of pathogenicity across lineages. We show that the predominant clones carry one or more lineage-associated virulence genes. The gene encoding staphylococcal protein A (SpA), a key virulence factor involved in immune evasion and a potential vaccine antigen, is deleted in 62% of isolates. Most importantly, we have discovered that the spa locus is a hot spot for recombination and horizontal gene transfer in S. pseudintermedius, where genes related to restriction modification, prophage immunity, mercury resistance, and nucleotide and carbohydrate metabolism have been acquired in different lineages. Our study also establishes that ST45 is composed of two distinct sublineages that differ in their accessory gene content and virulence potential. Collectively, this study reports several previously undetected lineage-associated genetic factors that may have a role in the clonal success of the major MDR MRSP clones. These data provide a framework for future experimental studies on S. pseudintermedius pathogenesis and for developing novel therapeutics against this pathogen.IMPORTANCEStaphylococcus pseudintermedius is a major canine pathogen but can also occasionally infect humans. Identification of genetic factors contributing to the virulence and clonal success of multidrug-resistant S. pseudintermedius clones is critical for the development of therapeutics against this pathogen. Here, we characterized the genome sequences of a global collection of 622 S. pseudintermedius isolates. We show that all major clones, besides carrying core virulence genes, which are present in all strains, carry one or more lineage-specific genes. Many of these genes have been acquired from other bacterial species through a horizontal gene transfer mechanism. Importantly, we have discovered that the staphylococcal protein A gene (spa), a widely used marker for molecular typing of S. pseudintermedius strains and a potential vaccine candidate antigen, is deleted in 62% of strains. Furthermore, the spa locus in S. pseudintermedius acts as a reservoir to accumulate lineage-associated genes with adaptive functions.

Positive and Negative Effects of Metal Oxide Nanoparticles on Antibiotic Resistance Genes Transfer.

Rapid development of antibiotic resistance in bacteria is a critical public health problem in the world. One of the main routes of resistance development is the transfer of genes containing antibiotic resistance cassettes. Gene transfer can be done through horizontal transfer of genes: transduction, conjugation, and transformation. Many factors in the environment influence these processes, and one of them is the action of metal oxide nanoparticles (MONPs), which can appear in the milieu through both biological synthesis and the release of engineered nanomaterial. In this study, the effect of AlOOH, CuO, Fe3O4, TiO2, and ZnO MONPs on the transformation (heat shock transformation) of bacteria Escherichia coli K12, and the conjugation between E. coli cc118 and E. coli Nova Blue were studied. The MONPs were synthesized by one method and fully characterized. ZnO nanoparticles (NPs) have significantly increased the efficiency of transformation (more than 9-fold), while the other NPs have reduced it to 31 times (TiO2 NPs). AlOOH NPs increased the number of transconjugants more than 1.5-fold, while CuO and Fe3O4 NPs did not have a significant effect on transformation and conjugation. Thus, the data shows that different types of MONPs can enhance or inhibit different gene transfer mechanisms, affecting the spread of antibiotic resistance genes.

Plasmid Transfer by Conjugation in Gram-Negative Bacteria: From the Cellular to the Community Level.

Bacterial conjugation, also referred to as bacterial sex, is a major horizontal gene transfer mechanism through which DNA is transferred from a donor to a recipient bacterium by direct contact. Conjugation is universally conserved among bacteria and occurs in a wide range of environments (soil, plant surfaces, water, sewage, biofilms, and host-associated bacterial communities). Within these habitats, conjugation drives the rapid evolution and adaptation of bacterial strains by mediating the propagation of various metabolic properties, including symbiotic lifestyle, virulence, biofilm formation, resistance to heavy metals, and, most importantly, resistance to antibiotics. These properties make conjugation a fundamentally important process, and it is thus the focus of extensive study. Here, we review the key steps of plasmid transfer by conjugation in Gram-negative bacteria, by following the life cycle of the F factor during its transfer from the donor to the recipient cell. We also discuss our current knowledge of the extent and impact of conjugation within an environmentally and clinically relevant bacterial habitat, bacterial biofilms.

Design and application of synthetic microbial communities

Microorganisms are ubiquitous in our world, and they form different communities between organisms and the surrounding environment. It is estimated that there are more than 108 bacteria in a small gram of soil, and there are more than 1013 bacteria in the human intestine. It is a complex ecosystem formed under the interaction mechanisms of resource competition, nutrient symbiosis, quorum sensing, and horizontal gene transfer. Among them, the microbial communities in the soil and hydrosphere environment play a key driving role in the global chemical cycle of carbon, nitrogen and other elements. In industrial production, the microbial communities can treat our waste and purify the environment. In the field of human diseases, the microbial community in the human intestine is closely related to the development, metabolism and immunity of the host. Therefore, studying the stability of the composition of the microbial community is of great significance for solving the problems of ecological environment, agricultural production, and human health. With the development of high-throughput sequencing technology, the diversity and stability of microbial communities in different environments have been deeply studied. Although the scientific community has paid more attention to microbial communities in recent years, there are still many difficulties before us effectively use these communities to meet social requirements and environmental challenges. Therefore, it is critical to use new scientific concepts such as synthetic biology to interpret existing scientific problems. Among them, the core cycle of synthetic biology, Design-Build-Test-Learn is expected to promote the perfection and discovery of the basic theory of microbial ecological communities, and promote the research and development of biotechnology lays a theoretical foundation for improving the application of human health, agricultural production and environmental pollution. The ecology of microbial communities in nature is highly complex, making it challenging to carry out reproducible, controllable perturbation experiments in natural ecosystems. In contrast, synthetic communities constructed in the laboratory using a “bottom-up” approach offer moderate complexity and high controllability, and can serve as a bridge between complex ecosystems and mathematical modeling. By combining synthetic microbial communities, quantitative models and sequencing techniques, we can systematically study interactions between microbial populations and predict the dynamics of microbial communities. In terms of application, research on synthetic microbial communities will provide critical insights for how to control and engineer complex microbial ecosystems, and help solve important problems in human health and agricultural production via the design of stable microbial communities with controllable functions. In this review article, we mainly focus on the construction methods and theoretical foundations of existing synthetic microbial communities and the potential applications of these communities from two aspects, namely the knowledge of creation and the application of creation. And we also discuss the potential application of synthetic biology methods in this field.

Transferable Plasmids of Salmonella enterica Associated With Antibiotic Resistance Genes.

Salmonella enterica is a common foodborne illness in the United States and globally. An increasing number of Salmonella infections are resistant to antibiotics, and many of the genes responsible for those resistances are carried by plasmids. Plasmids are important mediators of horizontal gene exchange, which could potentially increase the spread of antibiotic resistance (AR) genes. Twenty-eight different incompatibility groups of plasmids have been described in Enterobacteriaceae. Incompatibility groups differ in their accessory gene content, replication mechanisms, and their associations with Salmonella serotypes and animal sources. Plasmids also differ in their ability to conjugate or be mobilized, essential genes, and conditions required for transfer. It is important to understand the differences in gene content and transfer mechanisms to accurately determine the impact of plasmids on the dissemination and persistence of antibiotic resistance genes. This review will cover the most common plasmid incompatibility groups present in S. enterica with a focus on the transfer mechanisms and associated antibiotic resistance genes.

Horizontal \u2018gene drives\u2019 harness indigenous bacteria for bioremediation

Engineering bacteria to clean-up oil spills is rapidly advancing but faces regulatory hurdles and environmental concerns. Here, we develop a new technology to harness indigenous soil microbial communities for bioremediation by flooding local populations with catabolic genes for petroleum hydrocarbon degradation. Overexpressing three enzymes (almA, xylE, p450cam) in Escherichia coli led to degradation of 60–99% of target hydrocarbon substrates. Mating experiments, fluorescence microscopy and TEM revealed indigenous bacteria could obtain these vectors from E. coli through several mechanisms of horizontal gene transfer (HGT), including conjugation and cytoplasmic exchange through nanotubes. Inoculating petroleum-polluted sediments with E. coli carrying the vector pSF-OXB15-p450camfusion showed that the E. coli cells died after five days but a variety of bacteria received and carried the vector for over 60 days after inoculation. Within 60 days, the total petroleum hydrocarbon content of the polluted soil was reduced by 46%. Pilot experiments show that vectors only persist in indigenous populations when under selection pressure, disappearing when this carbon source is removed. This approach to remediation could prime indigenous bacteria for degrading pollutants while providing minimal ecosystem disturbance.

Experimental approaches to tracking mobile genetic elements in microbial communities.

Horizontal gene transfer is an important mechanism of microbial evolution and is often driven by the movement of mobile genetic elements between cells. Due to the fact that microbes live within communities, various mechanisms of horizontal gene transfer and types of mobile elements can co-occur. However, the ways in which horizontal gene transfer impacts and is impacted by communities containing diverse mobile elements has been challenging to address. Thus, the field would benefit from incorporating community-level information and novel approaches alongside existing methods. Emerging technologies for tracking mobile elements and assigning them to host organisms provide promise for understanding the web of potential DNA transfers in diverse microbial communities more comprehensively. Compared to existing experimental approaches, chromosome conformation capture and methylome analyses have the potential to simultaneously study various types of mobile elements and their associated hosts. We also briefly discuss how fermented food microbiomes, given their experimental tractability and moderate species complexity, make ideal models to which to apply the techniques discussed herein and how they can be used to address outstanding questions in the field of horizontal gene transfer in microbial communities.

Direct Visualization of Horizontal Gene Transfer by Transformation in Live Pneumococcal Cells Using Microfluidics.

Natural genetic transformation is a programmed mechanism of horizontal gene transfer in bacteria. It requires the development of competence, a specialized physiological state during which proteins involved in DNA uptake and chromosomal integration are produced. In Streptococcus pneumoniae, competence is transient. It is controlled by a secreted peptide pheromone, the competence-stimulating peptide (CSP) that triggers the sequential transcription of two sets of genes termed early and late competence genes, respectively. Here, we used a microfluidic system with fluorescence microscopy to monitor pneumococcal competence development and transformation, in live cells at the single cell level. We present the conditions to grow this microaerophilic bacterium under continuous flow, with a similar doubling time as in batch liquid culture. We show that perfusion of CSP in the microfluidic chamber results in the same reduction of the growth rate of individual cells as observed in competent pneumococcal cultures. We also describe newly designed fluorescent reporters to distinguish the expression of competence genes with temporally distinct expression profiles. Finally, we exploit the microfluidic technology to inject both CSP and transforming DNA in the microfluidic channels and perform near real time-tracking of transformation in live cells. We show that this approach is well suited to investigating the onset of pneumococcal competence together with the appearance and the fate of transformants in individual cells.

Transcriptome Analysis of Zygotic Induction During Conjugative Transfer of Plasmid RP4.

Conjugative transfer of bacterial plasmid is one of the major mechanisms of horizontal gene transfer, which is mediated by direct contact between donor and recipient cells. Gene expression of a conjugative plasmid is tightly regulated mostly by plasmid-encoded transcriptional regulators, but it remains obscure how differently plasmid genes are expressed in each cell during the conjugation event. Here, we report a comprehensive analysis of gene expression during conjugative transfer of plasmid RP4, which is transferred between isogenic strains of Pseudomonas putida KT2440 at very high frequency. To discriminate the expression changes in the donor and recipient cells, we took advantage of conjugation in the presence of rifampicin (Rif). Within 10 min of mating, we successfully detected transient transcription of plasmid genes in the resultant transconjugant cells. This phenomenon known as zygotic induction is likely attributed to derepression of multiple RP4-encoded repressors. Interestingly, we also observed that the traJIH operon encoding relaxase and its auxiliary proteins were upregulated specifically in the donor cells. Identification of the 5′ end of the zygotically induced traJ mRNA confirmed that the transcription start site of traJ was located 24-nt upstream of the nick site in the origin of transfer (oriT) as previously reported. Since the traJ promoter is encoded on the region to be transferred first, the relaxase may be expressed in the donor cell after regeneration of the oriT-flanking region, which in itself is likely to displace the autogenous repressors around oriT. This study provides new insights into the regulation of plasmid transfer processes.

Dissemination of Linezolid Resistance Through Sex Pheromone Plasmid Transfer in Enterococcus faecalis.

Despite recent recognition of the ATP-binding cassette protein OptrA as an important mediator of linezolid resistance in Enterococcus faecalis worldwide, the mechanisms of optrA gene acquisition and transfer remain poorly understood. In this study, we performed comprehensive molecular and phenotypic profiling of 44 optrA-carrying E. faecalis clinical isolates with linezolid resistance. Pulse-field gel electrophoresis and DNA hybridization revealed the presence of optrA in the plasmid in 26 (59%) isolates and in the chromosome in 18 (41%) isolates. Conjugation experiments showed a successful transfer of optrA in 88.5% (23/26) of isolates carrying optrA in plasmids while no transfer occurred in any isolates carrying optrA in the chromosome (0/18). All 23 transconjugants exhibited in vitro resistance to linezolid and several other antibiotics and were confirmed to contain optrA and other resistance genes. Plasmid typing demonstrated a predominance (18/23,78%) of rep9–type plasmids (pCF10 prototype) known to be the best studied sex pheromone responsive plasmids. Full plasmid genome sequencing of one isolate revealed the presence of drug resistance genes (optrA and fexA) and multiple sex pheromone response genes in the same plasmid, which represents the first sex pheromone responsive plasmid carrying optrA from a clinical isolate. PCR-based genotyping revealed the presence of three key sex pheromone response genes (prgA, prgB, and prgC) in 23 optrA-carrying isolates. Finally, functional studies of these isolates by clumping induction assay detected different degrees of clumping in 17 isolates. Our analysis suggests that optrA-mediated linezolid resistance can be widely disseminated through sex pheromone plasmid transfer.

Viral concentration methods for diversity studies in soil samples

Soil is the greatest reservoir of microorganisms, which are the main agents responsible for biogeochemical cycles, as well as for the decomposition of organic compounds and the supply of plant nutrients. Among all the microorganisms present in soil are the viruses, which influence the activity and ecology of other populations in the environment. As bacteria are the most common host of viruses in soil, most virus-like particles (VLPs) are considered to be bacteriophages. Since they can have an effect on the activity and ecology of bacteria, they can influence bacterial evolution by transduction, a mechanism of horizontal gene transfer in which the bacteriophage transfers DNA from one bacteria to another. Although viruses are the most abundant among all microorganisms and have great importance in the environment, viral diversity has not been well explored in soil. Because of this fact, the aim of the present study was to determine the best concentration method for the study of viral diversity. For that purpose, three concentration methods commonly used for viral study were selected and adapted to viral concentrations in soil samples: negatively charged HA membranes, polyethylene glycol (PEG) and ultracentrifugation (UF) were used, and viral diversity was evaluated by the random amplified polymorphic DNA (RAPD), transmission electron microscopy (TEM) and metagenomic approaches. Of the three concentration methods, the HA membrane showed the best results, more diverse in metagenomic analysis and with more VLP morphotypes, followed by ultracentrifugation. These techniques recovered viral particles of over 100 nm in size, while PEG recovered smaller particles. RAPD and TEM analyses were shown to be effective methods for the study of viral diversity, corroborating the data obtained by sequencing.

Targeting Plasmids to Limit Acquisition and Transmission of Antimicrobial Resistance.

Antimicrobial resistance (AMR) is a significant global threat to both public health and the environment. The emergence and expansion of AMR is sustained by the enormous diversity and mobility of antimicrobial resistance genes (ARGs). Different mechanisms of horizontal gene transfer (HGT), including conjugation, transduction, and transformation, have facilitated the accumulation and dissemination of ARGs in Gram-negative and Gram-positive bacteria. This has resulted in the development of multidrug resistance in some bacteria. The most clinically significant ARGs are usually located on different mobile genetic elements (MGEs) that can move intracellularly (between the bacterial chromosome and plasmids) or intercellularly (within the same species or between different species or genera). Resistance plasmids play a central role both in HGT and as support elements for other MGEs, in which ARGs are assembled by transposition and recombination mechanisms. Considering the crucial role of MGEs in the acquisition and transmission of ARGs, a potential strategy to control AMR is to eliminate MGEs. This review discusses current progress on the development of chemical and biological approaches for the elimination of ARG carriers.

The major subunit of widespread competence pili exhibits a novel and conserved type IV pilin fold

Type IV filaments (T4F), which are helical assemblies of type IV pilins, constitute a superfamily of filamentous nanomachines virtually ubiquitous in prokaryotes that mediate a wide variety of functions. The competence (Com) pilus is a widespread T4F, mediating DNA uptake (the first step in natural transformation) in bacteria with one membrane (monoderms), an important mechanism of horizontal gene transfer. Here, we report the results of genomic, phylogenetic, and structural analyses of ComGC, the major pilin subunit of Com pili. By performing a global comparative analysis, we show that Com pili genes are virtually ubiquitous in Bacilli, a major monoderm class of Firmicutes. This also revealed that ComGC displays extensive sequence conservation, defining a monophyletic group among type IV pilins. We further report ComGC solution structures from two naturally competent human pathogens, Streptococcus sanguinis (ComGCSS) and Streptococcus pneumoniae (ComGCSP), revealing that this pilin displays extensive structural conservation. Strikingly, ComGCSS and ComGCSP exhibit a novel type IV pilin fold that is purely helical. Results from homology modeling analyses suggest that the unusual structure of ComGC is compatible with helical filament assembly. Because ComGC displays such a widespread distribution, these results have implications for hundreds of monoderm species.

Investigation of the Directionality and Kinetics of DNA Transfer by a Bacterial Type IV Secretion System

Conjugation is the transfer of DNA from a donor cell to a recipient cell through a Type IV Secretion System (T4SS). The T4SS is encoded by the DNA conjugative element and is assembled in the donor cell membrane. T4SSs can also mediate the mobilization of resident plasmids that do not encode their own conjugation machinery from the donor to a recipient. In addition, in some cases, T4SSs have been shown to mediate retro‐transfer, or reverse mobilization, in which a donor cell containing the conjugative element receives DNA from a recipient cell. Conjugation, mobilization, and reverse mobilization are all important mechanisms of horizontal gene transfer that contribute to bacterial evolution and the spread of antibiotic resistance genes. Previously, it has been shown that the integrative and conjugative element ICEBs1 of Bacillus subtilis exhibits very high frequencies of conjugation and plasmid mobilization. Here, we compare the timing and frequency of ICEBs1‐dependent conjugation, plasmid mobilization, and reverse mobilization. Donor and recipient cells having different antibiotic markers were mixed and placed on solid filters for different periods of time to allow for DNA transfer. After incubation, the cell mixtures were plated on selective media to measure the frequency of DNA transfer. We found that both mating and plasmid mobilization can be detected within 2 minutes and peak after about 1–2 hours. Mating was generally more frequent than mobilization at most time points. Reverse mobilization was not detected until 1–2 hours, and was more than 100‐fold less frequent than mating. Reverse mobilization also required the transfer of T4SS genes to the recipient. Our data are consistent with the T4SS acting unidirectionally; in other words, reverse mobilization requires that a conjugative DNA element be transferred from donor to recipient prior to the recipient making its own T4SS that transfers DNA back into the donor.Support or Funding InformationThis research was supported by Suffolk University and an NSF‐RUI grant to M. Berkmen.

A review on cybrids : An approach for plant improvement

Somatic hybridization is a mechanism for gene transfer from related species to cultivated crops, especially when wide hybridization is not applicable. Protoplast fusion resulting in the development of cybrids is known as cybridization. Interaction of plastome and genome contributes to the formation of cybrids (cytoplasmic hybrids). Cybridization has been successfully used to transfer CMS in rice and maize. It is very promising allows partial genome transfer better tolerated than whole-genome transfer. It enables transfer of genetic materials between distantly-related and sexually-incompatible species with great potential for improvement of crops. It demands less common skills and expertise, but ranks as a method yielded good results. But introgression and stable inheritance of the alien DNA carrying the desired genes have to take place. Moreover, an important factor to investigate in the future is the mechanism involved in the incorporation of donor DNA into recipient chromosomes.