Showing papers by "Heidi B. Kaplan published in 2004"

Exopolysaccharide biosynthesis genes required for social motility in Myxococcus xanthus.

Abstract: Social (S)-motility in Myxococcus xanthus is a flagellum-independent gliding motility system that allows bacteria to move in groups on solid surfaces S-motility has been shown to require type IV pili (TFP), exopolysaccharide (EPS; a component of fibrils) and lipopolysaccharide (LPS) Previously, information concerning EPS biogenesis in M xanthus was lacking In this study, we screened 5000 randomly mutagenized colonies for defects in S-motility and EPS and identified two genetic regions essential for EPS biogenesis: the EPS synthesis (eps) region and the EPS-associated (eas) region Mutants with insertions in the eps and eas regions were defective in S-motility and fruiting body formation These mutants failed to bind the dye calcofluor white, indicating that they lacked EPS; however, they retained normal TFP and LPS Analysis of the eps locus showed several open reading frames (ORFs) that encode homologues to glycosyltransferases, glucanases and EPS transporters as well as regulatory proteins; the eas locus contains two ORFs: one exhibits homology to hypothetical proteins with a conserved domain of unknown function and the other displays no apparent homology to other proteins in the database Further genetic mutagenesis analysis indicates that the whole eps region is involved in the biosynthesis of fibrils and fibril EPS The operon at the proximal end of the eps region was analysed by generating in-frame deletion mutations These mutants showed varying degrees of defects in the bacterium's ability to produce EPS or perform EPS-related functions, confirming the involvement of these genes in M xanthus EPS biogenesis

Characterization of a Myxococcus xanthus mutant that is defective for adventurous motility and social motility

Abstract: Myxococcus xanthus is a gliding bacterium that possesses two motility systems, the adventurous (A-motility) and social (S-motility) systems A-motility is used for individual cell gliding, while S-motility is used for gliding in multicellular groups Video microscopy studies showed that nla24 cells are non-motile on agar surfaces, suggesting that the nla24 gene product is absolutely required for both A-motility and S-motility under these assay conditions S-motility requires functional type IV pili, wild-type LPS O-antigen, and an extracellular matrix of exopolysaccharide (EPS) and protein called fibrils The results of expression studies and tethering assays indicate that the nla24 mutant has functional type IV pili The nla24 mutant also produces wild-type LPS However, several lines of evidence suggest that the nla24 mutant is defective for production of the EPS portion of the fibril matrix The nla24 mutant is also defective for transcription of two genes (aglU and cglB) known to be required for A-motility, which is consistent with the idea that nla24 cells are defective for A-motility Based on these findings, it is proposed that the putative transcriptional activator Nla24 regulates a subset of genes that are important for A-motility and S-motility in M xanthus