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Phosphorus Limitation Enhances Biofilm Formation of the Plant Pathogen Agrobacterium tumefaciens through the PhoR-PhoB Regulatory System. Thomas Danhorn, 2004.The plant pathogen Agrobacterium tumefaciens forms architecturally complex biofilms on inert surfaces . Adherence of A . tumefaciens C58 was significantly enhanced under phosphate limitation compared to phosphate-replete conditions, despite slower overall growth under low-phosphate conditions . Replacement of Pi with sn-glycerol-3-phosphate and 2-aminoethylphosphonate yielded similar results . The increase in surface interactions under phosphate limitation was observed in both static culture and continuous-culture flow cells . Statistical analysis of confocal micrographs obtained from the flow cell biofilms revealed that phosphate limitation increased both the overall attached biomass and the surface coverage, whereas the maximum thickness of the biofilm was not affected . Functions encoded on the two large plasmids of A . tumefaciens C58, pTiC58 and pAtC58, were not required for the observed phosphate effect . The phosphate concentration at which increased attachment was observed triggered the phosphate limitation response, controlled in many bacteria by the two-component regulatory system PhoR-PhoB . The A . tumefaciens phoB and phoR orthologues could only be disrupted in the presence of plasmid-borne copies of the genes, suggesting that this regulatory system might be essential . Expression of the A . tumefaciens phoB gene from a tightly regulated inducible promoter, however, correlated with the amount of biofilm under both phosphate-limiting and nonlimiting conditions, demonstrating that components of the Pho regulon influence A . tumefaciens surface interactions . Micafungin Enhances Neutrophil Fungicidal Functions against Candida Pseudohyphae. Cristina Gil-Lamaignere, 2004.We evaluated the effect of the combination of micafungin and polymorphonuclear leukocytes (PMN) against hyphae of Candida albicans and Candida dubliniensis . Micafungin enhanced the PMN oxidative burst dose dependently . The combination was synergistic (C . albicans) or additive (C . dubliniensis); when PMN were pretreated with granulocyte-macrophage colony-stimulating factor, the combination was more effective . Characterization of a Mycoplasma pneumoniae hmw3 Mutant: Implications for Attachment Organelle Assembly. Melisa J. Willby, 2002.The proteins required for adherence of the pathogen Mycoplasma pneumoniae to host respiratory epithelial cells are localized to a polar structure, the attachment organelle . A number of these proteins have been characterized functionally by analysis of noncytadhering mutants, and many are components of the mycoplasma cytoskeleton . Mutations in some cytadherence-associated proteins have pleiotropic effects, including decreased stability of other proteins, loss of adherence and motility, and abnormal morphology . The function of protein HMW3, a component of the attachment organelle, has been difficult to discern due to lack of an appropriate mutant . In this paper, we report that loss of HMW3 resulted in decreased levels and more diffuse localization of cytoskeletal protein P65, subtle changes in morphology, inability to cluster the adhesin P1 consistently at the terminal organelle, reduced cytadherence, and, in some cells, an atypical electron-dense core in the attachment organelle . This phenotype suggests a role for HMW3 in the architecture and stability of the attachment organelle . Study of Second-Site Suppression in the pheP Gene for the Phenylalanine Transporter of Escherichia coli. Jing Pi, 2002.Site-directed mutagenesis was used to investigate a region of the PheP protein corresponding to the postulated consensus amphipathic region (CAR) in the GabP protein . Whereas some critical residues are conserved in both proteins, there are major differences between the two proteins which may reflect different functions for this region . Replacement of R317, Y313, or P341 by a number of other amino acids destroyed the PheP function . An R317E-E234R double mutant exhibited low levels of PheP transport activity, indicating that there is a possible interaction between these two residues in the wild-type protein . E234 is highly conserved in members of the superfamily of amino acid-polyamine-organocation transporters and also is critical for PheP function in the wild-type protein . Second-site suppressors were isolated for mutants with mutations in E234, Y313, R317, and P341 . Most suppressor mutations were found to cluster towards the extracellular face of spans III, IX, and X . Some mutations, such as changes at M116, were able to suppress each of the primary changes at positions E234, Y313, R317, and P341 but were unable to restore function to a number of other primary mutants . The possible implications of these results for the tertiary structure of the protein are discussed . Glucose-Related Dissociation between icaADBC Transcription and Biofilm Expression by Staphylococcus epidermidis: Evidence for an Additional Factor Required for Polysaccharide Intercellular Adhesin Synthesis. Sabine Dobinsky, 2003.Biofilm formation in Staphylococcus epidermidis depends, in the majority of the strains, on the activity of the icaADBC locus . The expression of the operon that encodes the synthetic enzymes of the intercellular polysaccharide adhesin (PIA) depends on a variety of exogenic environmental conditions and is, at least in part, regulated by the alternative sigma factor  B . We investigated the transcriptional regulation of the ica operon and the respective phenotypes expressed under growth conditions differing in the content of glucose in the growth medium . In the presence of glucose, S . epidermidis exhibited a PIA- and biofilm-positive phenotype whereas ica transcription was down-regulated in the postexponential and stationary phases of growth . Surprisingly, maximum transcription of ica was detectable in the stationary phase of growth in the absence of glucose despite the expression of a PIA- and biofilm-negative phenotype . In vitro enzymatic assays and phenotypic characterization showed that the abundant amount of ica mRNA was functionally active because induction of stationary-phase cells with glucose led to immediate PIA synthesis . Induction of biofilm formation could be completely inhibited by chloramphenicol, which, given at a later stage of biofilm accumulation, also inhibited further development of preformed biofilm, indicating that continuous translation of an additional, icaADBC-independent factor is required for the expression of a biofilm-positive phenotype .
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