suis (data not shown). Mutants also had a tendency to grow in longer chains of cells (Fig. 3). It is quite possible that the lower growth rate of the xer mutants might be related to a defect in chromosome segregation, as suggested by Chalker et al. (2000). Nucleoid morphology was investigated by DAPI-staining wild-type and mutant cells, and no significant morphological changes were seen, although anucleate cells were observed in about 10% of the population (data not shown). In coccus bacteria, dimensional changes resulting from perturbation of chromosome segregation may be rather subtle, as they have the potential to occur in more than one plane, and this may
explain why microscopy was insufficiently sensitive to detect the morphological changes. The sequence of XerS does not show any amino acid similarities to proteins involved in either septum formation/contraction or cell wall degradation, Selleck Vorinostat making a chromosomal segregation defect the most likely cause of the ‘chainy’ phenotype. A similar phenotype was observed with divIVA mutants of Streptococcus pyogenes (Fadda et al., 2007). Interestingly, this protein has been shown to interact with the cell division
protein FtsK. Our initial results (data not shown) have indicated protein–protein interactions between FtsK and XerS. Nolivos et al. (2010) have also found interactions between these proteins in L. lactis. Future investigations of the catalytic activity of XerS and its interaction between FtsK and other cellular proteins and DNA will allow us to determine how Xer recombination is regulated in Selleckchem BYL719 these medically important bacteria, and how this process may effect the growth and pathogenicity of S. suis. We thank Drs Josée Harel and Marcelo Gottschalk for S. suis p1/7 and Ceramide glucosyltransferase 31533 genomic DNA, S. suis strain S735 and plasmid pBEA756; Monique Vasseur for technical assistance with DIC microscopy and image analysis; and members of our laboratory their assistance and advice. This work was supported by grants from the National Science and Engineering Research Council of Canada (106085-06) and the Université de Montréal.
“Cry2Aa exhibits dual activity to Lepidoptera and Diptera. Cry2Ab differs in amino acid sequence from Cry2Aa by 13% and has shown significant lepidopteran activity, but no mosquitocidal activity. Previous studies implicate 23 Cry2Aa specificity-conferring residues of domain II, which differ in Cry2Ab. Nine residues are putatively involved in conferring Cry2Aa dipteran specificity. To explore Cry2Ab dipteran toxicity, site-directed mutagenesis was employed to exchange Cry2Ab residues with Cry2Aa D (dipteran) block residues. Cry2Ab wild type demonstrated high toxicity (LC50 of 540 ng mL−1) to Anopheles gambiae, but not to Aedes or Culex, within a 24-h time period. Cry2Ab should be reclassified as a dual active Cry toxin.