Summary Accumulation of antibiotic resistance among pathogenic bacteria has called attention to horizontal gene transfer that involves plasmids and transpozons. Integrons, usually placed on mobile genome elements, are very deeply engaged in the process of origin of multiple-drug-resistant strains. Integrons are genetic elements that contain determinants of the components of the site-specific recombination system that recognizes and captures mobile gene cassettes. More than 70 different antibiotic resistance genes covering most classes of antimicrobials presently in use have been detected in gene cassettes. Integrons are frequently found in clinical and environmental strains of gram-negative rods. The discovery of super-integrons, i.e. genetic structures gathering gene cassettes in a huge number, led to the conception of genome cassettes capture as an element of a broader phenomenon of bacterial genome modification in response to changing environmental conditions.
Acetobacter xylinum strains are known as very efficient producers of bacterial cellulose which, due to its unique properties, has great application potential. One of the most important problems faced during cellulose synthesis by these bacteria is generation of cellulose non-producing cells, which can appear under submerged culture conditions. The reasons of this remain unknow. These studies have been undertaken to compare at the molecular level wild-type, cellulose producing (Cel+) A. xylinum strains with Cel- forms of cellulose-negative phenotype. Comparison of protein profiles of both forms of A. xylinum by 2D electrophoresis allowed for the isolation of proteins which were produced exclusively by either Cel+ or Cel- cells. Sequences of peptides derived from these proteins were aligned with those of proteins deposited in databases. This analysis revealed that Cel- cells lacked two enzymes: phosphoglucomutase and glucose-1-phosphate uridylyltransferase, which generates UDP-glucose being the substrate for cellulose synthase. DNA was analyzed by ligation-mediated PCR carried out at low denaturation temperature (PCR-MP). Two DNA fragments of different thermal stability (218 and 217 bp) were obtained from the DNA of Cel+ and Cel- forms, respectively. The only difference between these Cel- and Cel+ DNA fragments is deletion of one T residue. Alignment of those two sequences with those deposited in the GenBank database revealed that similar fragments are present in the genomes of some bacterial cellulose producers and are located downstream from open reading frames (ORF) encoding phosphoglucomutase. The meaning of this observation is discussed.
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