Insertional inactivation of a Tet(K)/Tet(L) like transporter does not eliminate tetracycline resistance in

Bacillus cereus ATCC 10987 and ATCC 14579 can be induced to high levels of resistance to tetracycline. The chromosomal B. cereus gene bctl encodes a transmembrane protein with homology to Gram-positive tetracycline efflux proteins and relation to other members of the major facilitator superfamily of transport proteins. A mutant strain containing an insertionally inactivated bctl gene did not show impaired tetracycline resistance. No additional altered phenotype was observed in the mutant. Accumulation studies suggested that the resistance mechanism involves a reduced sensitivity to intracellular tetracycline. Keywords : Tetracycline resistance ; Major facilitator superfamily ; Active e#ux ; Transport ; Bacillus cereus 1. Introduction Bacterial resistance to tetracycline is mediated by two major mechanisms : ribosome protection and active e#ux. Bacillus spp. are known to contain tetracycline e#ux proteins from the related classes Tet(K) and Tet(L). The tet(K) and tet(L) genes are loc..

Nanoscale imaging of Bacillus thuringiensis flagella using atomic force microscopy

Bacterial flagella are currently recognized to mediate a number of functions besides their important role in motility. These appendages can act as attachment organelles, secretory systems, and as extremely potent stimuli of the innate immune response. Particularly, it has been proposed that one of the Bacillus cereus and Bacillus thuringiensis pore-forming toxins, Hemolysin BL, is secreted using the flagellar export apparatus and that strains displaying swarming motility may have a higher virulence potential than non-swarming strains. Since there is growing evidence that these organelles are important for cell surface interactions, the analysis of flagella and other cell surface components has become an important issue, especially in Gram-positive bacteria. Different methodologies are available for visualizing bacterial flagella using either optical or electronic microscopy. However, these approaches are not always satisfactory, do not always permit to observe flagella with a high-resolution and involve complicated, time-consuming protocols. Recent progress in applying atomic force microscopy (AFM) to microbiological samples has enabled researchers to observe the nanoscale surface architecture of living microbial cells, and to measure the localization and interactions of their individual constituents. In this study, we used AFM imaging to explore the cell surface nanomorphology of different B. thuringiensis strains, with an emphasis on flagella. To gain a comprehensive picture of flagella expression, we compared the structural properties of the well-known B. thuringiensis sv. israelensis and B. thuringiensis sv. kurstaki wild type strains with four B. thuringiensis sv. israelensis derivative strains (AND508, GBJ002, GBJ002Mut25 and GBJ002Mut30) exhibiting altered flagella production. The data provide novel insights into flagella expression in Gram-positive bacteria and demonstrate the power of using AFM in bacterial genetic studies for assessing the phenotypic characteristics of mutants altered in cell surface appendages

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