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Timothy M Vogel

Publications and source records attributed to Timothy M Vogel.

13 recordsLinked to original sources

Development of metagenomic DNA shuffling for the construction of a xenobiotic gene.

We describe a metagenomic DNA shuffling process by combining protein engineering process mutation generator and the high potential diversity of metagenomic DNA derived from the environment. Numerous previous shuffling processes attempted to recombine more or less related parental sequences. At the same time, metagenomic approaches unveiled a huge diversity of DNA sequences and genomes, which have not yet been identified to date. In this study, we attempted to combine these two approaches in order to regenerate a novel gene. Here, we present the possibility that DNA fragments from an entire microbial community (metagenome) might be available for the creation of novel genes capable of degrading pollutants. Metagenomic DNA extracted from non-polluted soil was shuffled in vitro to recreate the linA gene responsible for the first steps of lindane degradation. In this work, 74% of the ORF came from separate subsets of the metagenomic pool from a lindane-free and linA-free soil. Our results demonstrate that microbial community genetic diversity can serve as a source for novel gene construction during in vitro manipulation. This in vitro gene construction might also simulate the mosaic nature of novel genes. This demonstration might lead to other attempts to mimic bacterial adaptation and to construct degradative genes for novel compounds not yet released into the environment.

Bacteria↗

Development and validation of a prototype 16S rRNA-based taxonomic microarray for Alphaproteobacteria.

The microarray approach has been proposed for high throughput analysis of the microbial community by providing snapshots of the microbial diversity under different environmental conditions. For this purpose, a prototype of a 16S rRNA-based taxonomic microarray was developed and evaluated for assessing bacterial community diversity. The prototype microarray is composed of 122 probes that target bacteria at various taxonomic levels from phyla to species (mostly Alphaproteobacteria). The prototype microarray was first validated using bacteria in pure culture. Differences in the sequences of probes and potential target DNAs were quantified as weighted mismatches (WMM) in order to evaluate hybridization reliability. As a general feature, probes having a WMM > 2 with target DNA displayed only 2.8% false positives. The prototype microarray was subsequently tested with an environmental sample, which consisted of an Agrobacterium-related polymerase chain reaction amplicon from a maize rhizosphere bacterial community. Microarray results were compared to results obtained by cloning-sequencing with the same DNA. Microarray analysis enabled the detection of all 16S rRNA gene sequences found by cloning-sequencing. Sequences representing only 1.7% of the clone library were detected. In conclusion, this prototype 16S rRNA-based taxonomic microarray appears to be a promising tool for the analysis of Alphaproteobacteria in complex ecosystems.

Alphaproteobacteria↗

Plasmid-encoded gamma-hexachlorocyclohexane degradation genes and insertion sequences in Sphingobium francense (ex-Sphingomonas paucimobilis Sp+).

The lin genes encode the gamma-hexachlorocyclohexane (gamma-HCH or lindane) catabolic pathway in lindane-degrading strains. The location and stability of these genes have been explored in the lindane-degrading Sphingobium francense strain Sp+, and in two non-lindane-degrading mutants (Sp1- and Sp2-). The lin genes, linA, linB, linE and linX were localized by hybridization on three of the six plasmids of the S. francense strain Sp+ showing dispersal within the genome. The linC gene was detected by PCR, but was not detected by hybridization on any of the plasmids. The hybridization of the linA and linX genes was negative with the two non-lindane-degrading mutants S. francense strains, Sp1- and Sp2-. The dynamic of this genome associated with gene loss and acquisition, and plasmid rearrangement was explored by a search for associated insertion sequences. A new insertion sequence, ISSppa4, belonging to the IS21 family was detected and compared with IS6100 and ISsp1. Insertion sequence localization was explored on different hybridization patterns (plasmid, total genome) with the lindane-degrading Sp+ strain and the two non-degrading derivatives (Sp1-, Sp2-). Insertion sequence movement and plasmid rearrangement could explain the emergence of the non-lindane-degrading mutants.

Bacterial Proteins↗

Potential of a 16S rRNA-based taxonomic microarray for analyzing the rhizosphere effects of maize on Agrobacterium spp. and bacterial communities.

Bacterial diversity is central to ecosystem sustainability and soil biological function, for which the role of roots is important. The high-throughput analysis potential of taxonomic microarray should match the breadth of bacterial diversity. Here, the power of this technology was evidenced through methodological verifications and analysis of maize rhizosphere effect based on a 16S rRNA-based microarray developed from the prototype of H. Sanguin et al. (Environ. Microbiol. 8:289-307, 2006). The current probe set was composed of 170 probes (41 new probes in this work) that targeted essentially the Proteobacteria. Cloning and sequencing of 16S rRNA amplicons were carried out on maize rhizosphere and bulk soil DNA. All tested clones that had a perfect match with corresponding probes were positive in the hybridization experiment. The hierarchically nested probes were reliable, but the level of taxonomic identification was variable, depending on the probe set specificity. The comparison of experimental and theoretical hybridizations revealed 0.91% false positives and 0.81% false negatives. The microarray detection threshold was estimated at 0.03% of a given DNA type based on DNA spiking experiments. A comparison of the maize rhizosphere and bulk soil hybridization results showed a significant rhizosphere effect, with a higher predominance of Agrobacterium spp. in the rhizosphere, as well as a lower prevalence of Acidobacteria, Bacteroidetes, Verrucomicrobia, and Planctomycetes, a new taxon of interest in soil. In addition, well-known taxonomic groups such as Sphingomonas spp., Rhizobiaceae, and Actinobacteria were identified in both microbial habitats with strong hybridization signals. The taxonomic microarray developed in the present study was able to discriminate and characterize bacterial community composition in related biological samples, offering extensive possibilities for systematic exploration of bacterial diversity in ecosystems.

Cloning, Molecular↗

Natural Pseudomonas sp. strain N3 in artificial soil microcosms.

The lightning-competent Pseudomonas sp. strain N3, recently isolated from soil, has been used to study the extent of natural electrotransformation (NET) or lightning transformation as a horizontal gene transfer mechanism in soil. The variation of electrical fields applied to the soil with a laboratory-scale lightning system provides an estimate of the volume of soil affected by NET. Based on the range of the electric field that induces NET of Pseudomonas strain N3, the volume of soil, where NET could occur, ranges from 2 to 950 m(3) per lightning strike. The influence of DNA parameters (amount, size, and purity) and DNA soil residence time were also investigated. NET frequencies (electrotransformants/recipient cells) ranged from 10(-8) for cell lysate after 1 day of residence in soil to 4 x 10(-7) with a purified plasmid added immediately before the lightning. The electrical field gradient (in kilovolts per cm) also played a role as NET frequencies ranging from 1 x 10(-5) at 2.3 kV/cm to 1.7 x 10(-4) at 6.5 kV/cm.

Ecosystem↗

Type I polyketide synthases may have evolved through horizontal gene transfer.

Type I polyketide synthases (PKSI) are modular multidomain enzymes involved in the biosynthesis of many natural products of industrial interest. PKSI modules are minimally organized in three domains: ketosynthase (KS), acyltransferase (AT), and acyl carrier protein. The KS domain phylogeny of 23 PKSI clusters was determined. The results obtained suggest that many horizontal transfers of PKSI genes have occurred between actinomycetales species. Such gene transfers may explain the homogeneity and the robustness of the actinomycetales group since gene transfers between closely related species could mimic patterns generated by vertical inheritance. We suggest that the linearity and instability of actinomycetales chromosomes associated with their large quantity of genetic mobile elements have favored such horizontal gene transfers.

Acyltransferases↗

High molecular weight DNA recovery from soils prerequisite for biotechnological metagenomic library construction.

Soil is a complex environment considered as one of the main reservoirs of microbial diversity. However, the inability to cultivate most soil bacteria hampered fundamental attempts to determine the diversity of the prokaryotic world and limited its industrial exploitation. In the last 20 years, new methods have been developed to overcome these limitations based on the direct extraction of DNA from bacteria in their natural environment. In addition to fundamental research, the cloning of the extracted DNA for the development of metagenomic DNA clone libraries offers possibilities to discover novel bio-molecules through the expression of genes from uncultivated bacteria in surrogate bacterial hosts. However, such objectives require adapting DNA extraction methods and cloning strategies in order that entire gene clusters encoding biosynthetic pathway for secondary metabolites can be cloned. In this paper, we report that the size of DNA fragments extracted from soil varied in a range between less than 100 kb and more than 400 kb depending on the soil. The relatively limited size of DNA fragments extracted from some soil was not only due to mechanical, chemical or enzymatic shearing of the DNA during the extraction process but partly to the microbial growth status. Stimulating bacteria in situ by providing nutrients to the soil improved the size of extracted DNA, but it modified the bacterial community structure.

Bacteria↗

Effect of carbon and nitrogen input on the bacterial community structure of Neocaledonian nickel mine spoils.

Neocaledonian mine spoils are considered as an extreme environment because of their edaphic conditions, which are unfavourable for life. The principal characteristics of this soil are the high nickel content (20,000 ppm) and the very low carbon (0.2%) and nitrogen (0.01%) levels, which are certainly among the major limiting factors for heterotrophic bacterial growth. The aim of this work was to determine what changes could occur in the bacterial community structure of the mine spoils when a carbon and a nitrogen source were added. Soil bacterial response to nutrient addition was examined in both the mine spoils and an agricultural soil, which is characterized by normal levels of nutrients. 16S rRNA gene clone libraries constructed to characterize changes occurring in the different soil bacterial communities showed an important selection of Actinobacteria in the mine spoils as a consequence of nutrient amendment: Actinobacteria represented 75% and 96% of the bacterial community structure after succinate and glucose addition, respectively. This was observed only in the mine spoils and is probably a consequence of the extreme environmental conditions. Carbon amendment in the agricultural soil led to an increase in Firmicutes, mainly Bacillus sp.

Actinobacteria↗

Isolation of lightning-competent soil bacteria.

Artificial transformation is typically performed in the laboratory by using either a chemical (CaCl(2)) or an electrical (electroporation) method. However, laboratory-scale lightning has been shown recently to electrotransform Escherichia coli strain DH10B in soil. In this paper, we report on the isolation of two "lightning-competent" soil bacteria after direct electroporation of the Nycodenz bacterial ring extracted from prairie soil in the presence of the pBHCRec plasmid (Tc(r), Sp(r), Sm(r)). The electrotransformability of the isolated bacteria was measured both in vitro (by electroporation cuvette) and in situ (by lightning in soil microcosm) and then compared to those of E. coli DH10B and Pseudomonas fluorescens C7R12. The electrotransformation frequencies measured reached 10(-3) to 10(-4) by electroporation and 10(-4) to 10(-5) by simulated lightning, while no transformation was observed in the absence of electrical current. Two of the isolated lightning-competent soil bacteria were identified as Pseudomonas sp. strains.

Bacteria↗

Phylogenetic analysis of polyketide synthase I domains from soil metagenomic libraries allows selection of promising clones.

The metagenomic approach provides direct access to diverse unexplored genomes, especially from uncultivated bacteria in a given environment. This diversity can conceal many new biosynthetic pathways. Type I polyketide synthases (PKSI) are modular enzymes involved in the biosynthesis of many natural products of industrial interest. Among the PKSI domains, the ketosynthase domain (KS) was used to screen a large soil metagenomic library containing more than 100,000 clones to detect those containing PKS genes. Over 60,000 clones were screened, and 139 clones containing KS domains were detected. A 700-bp fragment of the KS domain was sequenced for 40 of 139 randomly chosen clones. None of the 40 protein sequences were identical to those found in public databases, and nucleic sequences were not redundant. Phylogenetic analyses were performed on the protein sequences of three metagenomic clones to select the clones which one can predict to produce new compounds. Two PKS-positive clones do not belong to any of the 23 published PKSI included in the analysis, encouraging further analyses on these two clones identified by the selection process.

Amino Acid Sequence↗

Intergeneric transfer of chromosomal and conjugative plasmid genes between Ralstonia solanacearum and Acinetobacter sp. BD413.

Conjugative transfer of a broad-host range plasmid and transformation-mediated transfer of chromosomal genes were found to occur at significant frequencies between Ralstonia solanacearum and Acinetobacter sp. in planta. These intergeneric gene transfers are related to the conditions provided by the infected plant, including the extensive multiplication of these two bacteria in planta and the development of a competence state in Acinetobacter sp. Although interkingdom DNA transfer from nuclear transgenic plants to these bacteria was not detectable, plants infected by pathogens (e.g., Ralstonia solanacearum) and co-colonized by soil saprophyte bacteria (e.g., Acinetobacter sp.) can be considered as potential "hot spots" for gene transfer, even between phylogenetically remote organisms.

Acinetobacter↗

Degradation and transformability of DNA from transgenic leaves.

The fate of transplastomic (chloroplast genome contains the transgene) tobacco plant DNA in planta was studied when the plant leaves were subjected to decay conditions simulating those encountered naturally, including grinding, incubation with cellulase or enzymes produced by Erwinia chrysanthemi, and attack by the plant pathogen Ralstonia solanacearum. Direct visualization of DNA on agarose gels, gene extraction yield (the number of amplifiable aadA sequences in extracted plant DNA), and the frequency that recipient bacteria can be transformed by plant DNA were used to evaluate the quality and quantity of plant DNA and the transgene. These measurements were used to monitor the physical and biological degradation of DNA inside decaying plant tissues. Our results indicate that while most of the DNA will be degraded inside plant cells, sufficient DNA persists to be released into the soil.

Acinetobacter calcoaceticus↗

In situ transfer of antibiotic resistance genes from transgenic (transplastomic) tobacco plants to bacteria.

Interkingdom gene transfer is limited by a combination of physical, biological, and genetic barriers. The results of greenhouse experiments involving transplastomic plants (genetically engineered chloroplast genomes) cocolonized by pathogenic and opportunistic soil bacteria demonstrated that these barriers could be eliminated. The Acinetobacter sp. strain BD413, which is outfitted with homologous sequences to chloroplastic genes, coinfected a transplastomic tobacco plant with Ralstonia solanacearum and was transformed by the plant's transgene (aadA) containing resistance to spectinomycin and streptomycin. However, no transformants were observed when the homologous sequences were omitted from the Acinetobacter sp. strain. Detectable gene transfer from these transgenic plants to bacteria were dependent on gene copy number, bacterial competence, and the presence of homologous sequences. Our data suggest that by selecting plant transgene sequences that are nonhomologous to bacterial sequences, plant biotechnologists could restore the genetic barrier to transgene transfer to bacteria.

Acinetobacter↗