Viability and genetic stability of the bacterium Escherichia coli HB101 with the recombinant plasmid during preservation by various methods

A Fast and Easily Parallelizable Biosensor Method for Measuring Extractable Tetracyclines in Soils

Quantification of extractable antibiotics in soils is important to assessing their bioavailability and mobility, and ultimately their ecotoxicological and health risks. This study aimed to establish a biosensor method for detecting extractable tetracyclines in soils (Alfisol, Mollisol, and Ultisol) using whole-cell biosensors containing a reporter plasmid (pMTGFP or pMTmCherry) carrying fluorescent protein genes tightly controlled by tetracyclines-responsive control region (tetRO). This whole-cell biosensor method can simultaneously measure 96 or more samples within 6 h and is easily parallelizable, whereas a typical high-performance liquid chromatography (HPLC) method may require 7 times more of analysis time and much greater cost to achieve similar analytical throughput. The biosensor method had a detection limit for each of six tetracyclines between 5.32-10.2 μg/kg soil, which is considered adequate for detecting tetracyclines in ethylenediaminetetraacetic acid (EDTA) extracts of soils. Relative standard deviation was between 19.8-51.2% for the biosensor Escherichia coli DH5α/pMTGFP and 2.98-25.8% for E. coli DH5α/pMTmCherry, respectively, suggesting that E. coli DH5α/pMTmCherry was superior to E. coli DH5α/pMTGFP for detecting extractable tetracyclines in soils. This new, fast, easily parallelizable, and cost-effective biosensor method has the potential for measuring extractable concentrations of tetracyclines for a large number of soil samples in large-scale monitoring studies.

Métodos de conservación para actinobacterias con actividad solubilizadora de fósforo

El objetivo de esta investigación fue evaluar diferentes métodos de conservación para actinobacterias solubilizadoras de fósforo debido a la poca información de métodos específicos reportados para estos microorganismos. Los métodos de conservación se evaluaron a 3 diferentes periodos de tiempo; largo, mediano y corto plazo, usando métodos de congelación y liofilización; arcilla, sílica, arena  y transferencia periódica, respectivamente. Para ello se usaron 15 aislamientos de 3 localidades diferentes (La Vega, Maní y Tota) y un banco de referencia de la Unidad de Investigaciones Agropecuarias de la Pontificia Universidad Javeriana. Se prepararon todos los inóculos en solución salina al 0,85% (p/v) y se ajustaron a una concentración de 108 cel/mL, seguido a ello se inocularon los viales de cada método de conservación con sus respectivos crioprotectantes, glicerol 20% (v/v), 30% (v/v) para congelación y skim milk 18% (p/v) para liofilización. Los métodos a mediano plazo se ejecutaron de igual manera, el inóculo se agregó a 10 perlas de arcilla, 10 g de arena y 5 g de sílica, posteriormente se almacenaron a 4ºC. El método de corto plazo se evaluó en agar avena (15 g/L). La evaluación se realizó mediante recuento directo en cámara de Neubauer por la técnica de azul de tripán, además de la caracterización macroscópica y microscópica de cada aislamiento en transferencia periódica. Se estableció que la actividad solubilizadora de fósforo se mantuvo más estable en los métodos de glicerol 30 % (p/v) y liofilización según el análisis estadístico.  Palabras clave: viabilidad, crioprotectantes, banco, liofilización, crioconservación.

Rapid detection of tetracyclines and their 4-epimer derivatives from poultry meat with bioluminescent biosensor bacteria

Tetracycline (TC) specific luminescent bacterial biosensors were used in a rapid TC residue assay sensitized to meet the EU maximum residue limit (MRL) for TC residues in poultry muscle tissue (100 microg kg(-1)) by membrane-permeabilizing and chelating agents polymyxin B and EDTA. Sensitivities of 5 ng g(-1) for doxycycline, 7.5 ng g(-1) for chlortetracycline, and 25 ng g(-1) for tetracycline and oxytetracycline were reached. Except for doxycycline, the MRLs of these tetracyclines include their 4-epimer metabolites. In the biosensor assay, all four 4-epimers showed induction capacity and antimicrobial activity, and antimicrobial activity was also observed in the inhibition assay, although with lower efficiency than that of the corresponding parent compound in both assays. The biosensor assay is an inexpensive and rapid high-throughput screening method for the detection of 4-epimer TC residues along with their parent compounds.

Effects of long-term storage on plasmid stability in Bacillus anthracis

The plasmid profiles of 619 cultures of Bacillus anthracis which had been isolated and stored between 1954 and 1989 were analyzed using the Laboratory Response Network real-time PCR assay targeting a chromosomal marker and both virulence plasmids (pXO1 and pXO2). The cultures were stored at ambient temperature on tryptic soy agar slants overlaid with mineral oil. When data were stratified by decade, there was a decreasing linear trend in the proportion of strains containing both plasmids with increased storage time (P < 0.001). There was no significant difference in the proportion of strains containing only pXO1 or strains containing only pXO2 (P = 0.25), but there was a statistical interdependence between the two plasmids (P = 0.004). Loss of viability of B. anthracis cultures stored on agar slants is also discussed.

DNA Shuttling Between Plasmid Vectors and a Genome Vector: Systematic Conversion and Preservation of DNA Libraries Using the Bacillus subtilis Genome (BGM) Vector

The combined use of the contemporary vector systems, the bacterial artificial chromosome (BAC) vector and the Bacillus subtilis genome (BGM) vector, makes possible the handling of giant-length DNA (above 100 kb). Our newly constructed BGM vector efficiently integrated DNA prepared in the BAC vector. A BAC library comprised of 18 independent clones prepared from mitochondrial DNA (mtDNA) of Arabidopsis thaliana was converted to a parallel BGM library using the new BGM vector. The effectiveness of the combined use of the vector systems was confirmed by the stable recovery of all 18 DNAs as BAC clones from the respective BGM clones. We show that DNA in BGM was stably preserved at room temperature after spore formation of the host B.subtilis. Rapid and stable shuttling between Escherichiacoli and the B. subtilis host, combined with spore-mediated DNA storage, may facilitate the long-term and low-cost preservation and the transportation of DNA resources.

Detection of organomercurials with sensor bacteria

Mercury and its organic compounds, especially methylmercury, are hazardous compounds that concentrate in biota via biomagnification and cause severe neurological disorders in animals. In this paper, a recombinant whole-cell bacterial sensor for the detection of the organic compounds of mercury was constructed. The sensor carries firefly luciferase gene as a reporter under the control of the mercury-inducible regulatory part of broad spectrum mer operon from pDU1358. In addition, a gene-encoding organomercurial lyase (an enzyme necessary for cleavage of the mercury-carbon bond) was coexpressed in the sensor strain. The sensitivity of the sensor was evaluated on some environmentally important organomercurial compounds. The lowest detectable concentrations were 0.2 nM (50 ng/L), 1 nM (0.34 microg/L), and 10 microM (2.3 mg/L) for methylmercury chloride, phenylmercury acetate, and dimethylmercury, respectively. The sensor responded also to inorganic mercury and, therefore, using the sensor described here together with sensor bacteria responding only to inorganic mercury, it should be possible to characterize the mercury contamination, for example, in environmental samples.

Detection of tetracyclines with luminescent bacterial strains

The performance of two bioluminescent Escherichia coli K-12 strains for the specific detection of the tetracycline family of antimicrobial agents was compared, and the analytical applicability of one of the strains was preliminarily evaluated. One sensor plasmid contained the bacterial luciferase operon of Photorhabdus luminescens under the control of the tetracycline-responsive element from transposon Tn10 (15). An analogous plasmid construction with firefly (Photinus pyralis) luciferase reporter gene was constructed, and these two divergent tetracycline-inducible light-emitting systems were compared for their suitability for the qualitative detection of tetracyclines. Both sensor strains behaved in a similar manner kinetically, and the most sensitive tetracycline response for both sensor strains was achieved in 90-120 min by performing the assay at 37 degrees C. The sensor strain containing the bacterial luciferase operon responded slightly more sensitively to different tetracyclines than the strain containing firefly luciferase gene. The sensor bacteria retained their inducibility in lyophilization, and freeze-dried cells detected tetracyclines as sensitively as freshly cultivated sensor cells. The preliminary results from the analysis of tetracycline-spiked pork serum samples indicated that these sensor bacteria could be used to screen veterinary samples for tetracycline residues in real-time.

A group-specific microbiological test for the detection of tetracycline residues in raw milk

The potentiality of using a luminescent Escherichia coli strain for the specific detection of tetracycline residues in raw bovine milk was investigated. The sensor cells contain a reporter plasmid carrying the bacterial luciferase operon of Photorhabdus luminescens under the control of the tetracycline responsive control region from transposon Tn10. Incubation of the cells with the sample containing tetracyclines increases the light emission of the sensor cells. The most sensitive tetracycline detection was achieved in 120 min and by using CDTA as a chelating agent in the assay. Heat-treatment of milk before the assay decreased the variations in background luminescence signals and in tetracycline-induced luminescence between different milk samples. The detection limits for tetracycline, oxytetracycline, chlortetracycline, doxycycline, methacycline, demeclocycline, and minocycline were between 2 and 35 ng/mL. Nontetracycline antibiotics did not significantly interfere with the detection of tetracyclines.

Measurement of firefly luciferase reporter gene activity from cells and lysates using Escherichia coli arsenite and mercury sensors

The structural gene encoding firefly luciferase from Photinus pyralis is a widely used reporter both in traditional monitoring of gene expression and in bacterial sensors. Its activity can be detected from living cells (in vivo) without disruption or from cell-free lysate (in vitro). We compared the two measurement methods by using an overall toxicity detecting strain Escherichia coli MC1061(pCSS810), a mercury-sensing strain E. coli MC1061(pTOO11), and two new arsenic sensor strains MC1061(pTOO31) and AW3110(pTOO31) which were constructed for this study. Plasmid pTOO31 was constructed by inserting the ars promoter and the arsR gene from plasmid R773 to control firefly luciferase gene expression. Both in vivo and in vitro methods correlated well with the strains tested [correlation coefficients R = 0.99484 and 0.99834] and gave highly comparable results with standard solutions of arsenite or mercury ions and from six environmental water samples spiked with the ions. Use of the in vivo method resulted in lower variation between replicates of the same sample (CVs ranging from 3.9 to 7.2%) and also between different samples (from 8.6 to 25.9%) compared to the in vitro method (CVs ranging from 8.6 to 17.8% for replicates and from 13.1 to 36.3% for different samples).

Luminescent bacterial sensor for cadmium and lead

A sensor plasmid was constructed by inserting the regulation unit from the cadA determinant of plasmid pI258 to control the expression of firefly luciferase. The resulting sensor plasmid pTOO24 is capable of replicating in Gram-positive and Gram-negative bacteria. The expression of the reporter gene as a function of added extracellular heavy metals was studied in Staphylococcus aureus strain RN4220 and Bacillus subtilis strain BR151. Strain RN4220(pTOO24) mainly responded to cadmium, lead and antimony, the lowest detectable concentrations being 10 nM, 33 nM and 1 nM respectively. Strain BR151(pTOO24) responded to cadmium, antimony, zinc and tin at concentrations starting from 3.3 nM, 33 nM, 1 microM, and 100 microM, respectively. The luminescence ratios between induced and uninduced cells, the induction coefficients, of strains RN4220(pTOO24) and BR151(pTOO24) were 23-50 and about 5, respectively. These results were obtained with only 2-3 h incubation times. Freeze-drying of the sensor strains had only moderate effects on the performance with respect to sensitivity or induction coefficients.

Recombinant luminescent bacteria for measuring bioavailable arsenite and antimonite

Luminescent bacterial strains for the measurement of bioavailable arsenite and antimony were constructed. The expression of firefly luciferase was controlled by the regulatory unit of the ars operon of Staphylococcus aureus plasmid pI258 in recombinant plasmid pTOO21, with S. aureus RN4220, Bacillus subtilis BR151, and Escherichia coli MC1061 as host strains. Strain RN4220(pTOO21) was found to be the most sensitive for metal detection responding to arsenite, antimonite, and cadmium, the lowest detectable concentrations being 100, 33, and 330 nM, respectively. Strains BR151(pTOO21) and MC1061(pTOO21) responded to arsenite, arsenate, antimonite, and cadmium, the lowest detectable concentrations being 3.3 and 330 microM and 330 and 330 nM with BR151(pTOO21), respectively, and 3.3, 33, 3.3, and 33 microM with MC1061(pTOO21), respectively. In the absence of the mentioned ions, the expression of luciferase was repressed and only a small amount of background light was emitted. Other ions did not notably interfere with the measurement in any of the strains tested. Freeze-drying of the cells did not decrease the sensitivity of the detection of arsenite; however, the induction coefficients were somewhat lower.

Use of controlled luciferase expression to monitor chemicals affecting protein synthesis

In this article, we present a new bioluminescent test system for the screening of chemical compounds with an inhibitory effect on protein synthesis. The test is based on the measurement of real-time in vivo light production by Escherichia coli strains expressing different luciferase genes. The eukaryotic lucGR gene from Pyrophorus plagiophthalamus was found to be the best of three types of luciferase genes tested. Chemicals with known inhibitory effects on protein synthesis were used as test chemicals together with some general toxicants. The incubation of a test chemical with cells was performed either prior to or after the induction of protein synthesis, and the difference in the results of the two methods distinguishes the possible influence on protein synthesis from direct metabolic inhibition. Using lyophilized bacteria, the test is performed in less than an hour without any bacterial cultivation, which makes the test suitable for rapid and sensitive screening of chemicals or environmental samples. Compared with the standardized 50% inhibitory concentration calculation method of the bioluminescent cytotoxicity test, the more direct approach of calculation developed in this study proved to be more convenient than and as reliable as the standard method.

Long-term effects of embryo freezing in mice

Embryo cryopreservation does not induce clear-cut anomalies at detectable rates, but several mechanisms exist for nonlethal damage during the freeze-thaw process, and the risk of moderate or delayed consequences has not been extensively investigated. In a long-term study including senescence, we compared cryopreserved and control mice for several quantitative traits. Significant differences were seen in morphophysiological and behavioral features, some of them appearing in elderly subjects. Thus, apart from its immediate toxicity, embryo cryopreservation, without being severely detrimental, may have delayed effects. These results, consistent with other findings, question the neutrality of artificial reproductive technologies and draw attention to the preimplantation stages in developmental toxicology.