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rpoB Mutations in Streptococcus mitis Clinical Isolates Resistant to Rifampin. Wafa Achour, 2004.Activity of rifampin against 129 Streptococcus mitis isolates obtained from patients with hematologic cancer was investigated . One hundred twenty-five strains were susceptible to rifampin, and 4 were resistant (MIC = 32 to 64 µg/ml) . Resistance to rifampin was related to mutations in the rpoB gene: His526Asn in three strains and His526Asp in one strain . Identification and Characterization of the Novel LysM Domain-Containing Surface Protein Sep from Lactobacillus fermentum BR11 and Its Use as a Peptide Fusion Partner in Lactobacillus and Lactococcus. Mark S. Turner, 2004.Examination of supernatant fractions from broth cultures of Lactobacillus fermentum BR11 revealed the presence of a number of proteins, including a 27-kDa protein termed Sep . The amino-terminal sequence of Sep was determined, and the gene encoding it was cloned and sequenced . Sep is a 205-amino-acid protein and contains a 30-amino-acid secretion signal and has overall homology (between 39 and 92% identity) with similarly sized proteins of Lactobacillus reuteri, Enterococcus faecium, Streptococcus pneumoniae, Streptococcus agalactiae, and Lactobacillus plantarum . The carboxy-terminal 81 amino acids of Sep also have strong homology (86% identity) to the carboxy termini of the aggregation-promoting factor (APF) surface proteins of Lactobacillus gasseri and Lactobacillus johnsonii . The mature amino terminus of Sep contains a putative peptidoglycan-binding LysM domain, thereby making it distinct from APF proteins . We have identified a common motif within LysM domains that is shared with carbohydrate binding YG motifs which are found in streptococcal glucan-binding proteins and glucosyltransferases . Sep was investigated as a heterologous peptide expression vector in L . fermentum, Lactobacillus rhamnosus GG and Lactococcus lactis MG1363 . Modified Sep containing an amino-terminal six-histidine epitope was found associated with the cells but was largely present in the supernatant in the L . fermentum, L . rhamnosus, and L . lactis hosts . Sep as well as the previously described surface protein BspA were used to express and secrete in L . fermentum or L . rhamnosus a fragment of human E-cadherin, which contains the receptor region for Listeria monocytogenes . This study demonstrates that Sep has potential for heterologous protein expression and export in lactic acid bacteria . DNA Inversion on Conjugative Plasmid pVT745. Jinbiao Chen, 2002.Plasmid pVT745 from Actinobacillus actinomycetemcomitans strain VT745 can be transferred to other A . actinomycetemcomitans strains at a frequency of 10-6 . Screening of transconjugants revealed that the DNA of pDMG21A, a pVT745 derivative containing a kanamycin resistance gene, displayed a structural rearrangement after transfer . A 9-kb segment on the plasmid had switched orientation . The inversion was independent of RecA and required the activity of the pVT745-encoded site-specific recombinase . This recombinase, termed Inv, was highly homologous to invertases of the Din family . Two recombination sites of 22 bp, which are arranged in opposite orientation and which function as DNA crossover sequences, were identified on pVT745 . One of the sites was located adjacent to the 5' end of the invertase gene, inv . Inversion of the 9-kb segment on pVT745 derivatives has been observed in all A . actinomycetemcomitans strains tested except for the original host, VT745 . This would suggest that a host factor that is either inactive or absent in VT745 is required for efficient recombination . Inactivation of the invertase in the donor strain resulted in a 1,000-fold increase in the number of transconjugants upon plasmid transfer . It is proposed that an activated invertase causes the immediate loss of the plasmid in most recipient cells after mating . No biological role has been associated with the invertase as of yet .
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