Comparison of Intraplasmid Rearrangements in Escherichia coli 

Luka Bočkor¹, Srećko Jelenić^†, Nenad Malenica, Jelena Mlinarec, Višnja Besendorfer and Ivana Ivančić-Baće^*

University of Zagreb, Faculty of Science, Department of Molecular Biology, Horvatovac 102a, HR-10000 Zagreb, Croatia
¹Current address: ICGEB, AREA Science Park, Padriciano 99, IT-34149 Trieste, Italy

Article history:
Received September 4, 2012
Accepted July 15, 2013

Key words:
RecA, intramolecular recombination, Agrobacterium tumefaciens, Escherichia coli

Summary:
In this work we have constructed a plasmid to compare intraplasmid recombination efficiency in Agrobacterium tumefaciens and Escherichia coli. The plasmid contains two directly repeated copies of spectinomycin resistance gene, one lacking 5’ and the other lacking 3’ end. These two copies share a 570-bp region of homology and are separated by the ampicillin resistance gene. Homologous recombination between repeated copies of incomplete spectinomycin resistance genes results in the restoration of spectinomycin resistance. During this process, ampicillin resistance gene is either deleted or incomplete spectinomycin genes are amplified along with the ampicillin resistance gene. This experimental system enabled us to follow for the first time the generation of deletions and amplifications during intraplasmid recombination in A. tumefaciens. We show here that predominantly RecA-independent mechanism contributes to the formation of deletion and amplification products in both, A. tumefaciens and E. coli. Additionally, deletion and amplification products were detected at similar frequencies, suggesting that amplifications and deletions probably occur by a similar mechanism.

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Contents, Author and Subject Index

Electroporation Enhances the Metabolic Activity of Lactobacillus plantarum 564

Sanja Seratlić^1*, Branko Bugarski¹, Zorica Radulović², Petr Dejmek³, Lars Wadsö⁴ and Viktor Nedović<sup>2

1</sup>University of Belgrade, Faculty of Technology and Metallurgy, Department of Chemical Engineering, Karnegijeva 4, RS-11120 Belgrade, Serbia
²University of Belgrade, Faculty of Agriculture, Department of Food Technology, Nemanjina 6, RS-11080 Belgrade, Serbia
³Lund University, Faculty of Engineering – LTH, Department of Food Technology, Engineering and Nutrition, P.O. Box 124, SE-22100 Lund, Sweden
⁴Lund University, Faculty of Engineering – LTH, Division of Building Materials, P.O. Box 118, SE-22100 Lund, Sweden

Article history:
Received March 19, 2013
Accepted June 26, 2013

Key words:
Lactobacillus plantarum, pulsed electric fields, isothermal calorimetry

Summary:
The exposure of bacterial cells to pulsed electric fields (PEF) leads to the reversible formation of pores in the cell membrane if an applied energy is below the critical level. Therefore, the effect of electric field pulses with amplitudes below 14 kV/cm and the applied energy up to 12.2 J/cm³ on the growth of Lactobacillus plantarum 564 cells was investigated. After PEF treatments, the growth of lactobacilli in De Man-Rogosa-Sharpe broth at 37 °C was monitored by isothermal calorimetry, absorbance and plate counts. All the applied treatments resulted in a higher growth rate of PEF-treated cells during early and mid-log phase, especially bacterial samples treated with lower field intensities (1.3–5.5 J/cm³). The transport of ions and molecules through the cell membrane (which facilitates the growth of electroporated lactobacilli) was particularly evident in the mid-exponential growth phase, where the doubling time was reduced more than 3 times after the exposure to electric pulses of 5.5 J/cm³. The heat production rate during the growth of electroporated cells was also higher, indicating the enhanced metabolic activity of PEF-treated cells. Moreover, the electroporated cells had a better acidification ability than the untreated ones. It can be summarized that the applied PEF treatments with an energy input of below 12 J/cm³ potentially induce reversible electroporation of the cell membrane, which has a positive impact on the growth and metabolic activity of the cells of lactobacilli.

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