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Assembly Dynamics of FtsZ Rings in Bacillus subtilis and Escherichia coli and Effects of FtsZ-Regulating Proteins. David E. Anderson, 2004.FtsZ is the major cytoskeletal component of the bacterial cell division machinery . It forms a ring-shaped structure (the Z ring) that constricts as the bacterium divides . Previous in vivo experiments with green fluorescent protein-labeled FtsZ and fluorescence recovery after photobleaching have shown that the Escherichia coli Z ring is extremely dynamic, continually remodeling itself with a half time of 30 s, similar to microtubules in the mitotic spindle . In the present work, under different experimental conditions, we have found that the half time for fluorescence recovery of E . coli Z rings is even shorter (  9
s) . As before, the turnover appears to be coupled to GTP hydrolysis,
since the mutant FtsZ84 protein, with reduced GTPase in vitro,
showed an
3-fold
longer half time . We have also extended the studies to Bacillus
subtilis and found that this species exhibits equally rapid
dynamics of the Z ring (half time,
8
s) . Interestingly, null mutations of the FtsZ-regulating proteins
ZapA, EzrA, and MinCD had only modest effects on the assembly
dynamics . This suggests that these proteins do not directly regulate
FtsZ subunit exchange in and out of polymers . In B . subtilis,
only 30 to 35% of the FtsZ protein was in the Z ring, from which we
conclude that a Z ring only 2 or 3 protofilaments thick can function
for cell division .
Chemotaxis of Silicibacter sp . Strain TM1040 toward Dinoflagellate Products. Todd R. Miller, 2004.The  -proteobacteria phylogenetically related to the Roseobacter clade are predominantly responsible for the degradation of organosulfur compounds, including the algal osmolyte dimethylsulfoniopropionate (DMSP) . Silicibacter sp . strain TM1040, isolated from a DMSP-producing Pfiesteria piscicida dinoflagellate culture, degrades DMSP, producing 3-methylmercaptopropionate . TM1040 possesses three lophotrichous flagella and is highly motile, leading to a hypothesis that TM1040 interacts with P . piscicida through a chemotactic response to compounds produced by its dinoflagellate host . A combination of a rapid chemotaxis screening assay and a quantitative capillary assay were used to measure chemotaxis of TM1040 . These bacteria are highly attracted to dinoflagellate homogenates; however, the response decreases when homogenates are preheated to 80°C . To help identify the essential attractant molecules within the homogenates, a series of pure compounds were tested for their ability to serve as attractants . The results show that TM1040 is strongly attracted to amino acids and DMSP metabolites, while being only mildly responsive to sugars and the tricarboxylic acid cycle intermediates . Adding pure DMSP, methionine, or valine to the chemotaxis buffer resulted in a decreased response to the homogenates, indicating that exogenous addition of these chemicals blocks chemotaxis and suggesting that DMSP and amino acids are essential attractant molecules in the dinoflagellate homogenates . The implication of Silicibacter sp . strain TM1040 chemotaxis in establishing and maintaining its interaction with P . piscicida is discussed .
Nested Evolution of a tRNALeu(UAA) Group I Intron by both Horizontal Intron Transfer and Recombination of the Entire tRNA Locus. Knut Rudi, 2002.The origin and evolution of bacterial introns are still controversial issues . Here we present data on the distribution and evolution of a recently discovered divergent tRNALeu(UAA) intron . The intron shows a higher sequence affiliation with introns in tRNAIle(CAU) and tRNAArg(CCU) genes in  - and ß-proteobacteria, respectively, than with other cyanobacterial tRNALeu(UAA) group I introns . The divergent tRNALeu(UAA) intron is sporadically distributed both within the Nostoc and the Microcystis radiations . The complete tRNA gene, including flanking regions and intron from Microcystis aeruginosa strain NIVA-CYA 57, was sequenced in order to elucidate the evolutionary pattern of this intron . Phylogenetic reconstruction gave statistical evidence for different phylogenies for the intron and exon sequences, supporting an evolutionary model involving horizontal intron transfer . The distribution of the tRNA gene, its flanking regions, and the introns were addressed by Southern hybridization and PCR amplification . The tRNA gene, including the flanking regions, were absent in the intronless stains but present in the intron-containing strains . This suggests that the sporadic distribution of this intron within the Microcystis genus cannot be attributed to intron mobility but rather to an instability of the entire tRNALeu(UAA) intron-containing genome region . Taken together, the complete data set for the evolution of this intron can best be explained by a model involving a nested evolution of the intron, i.e., wherein the intron has been transferred horizontally (probably through a single or a few events) to a tRNALeu(UAA) gene which is located within a unstable genome region .
Characterization of Transcriptional Regulation of Shewanella frigidimarina Fe(III)-Induced Flavocytochrome c Reveals a Novel Iron-Responsive Gene Regulation System. Francisca Reyes-Ramirez, 2003.The bacterium Shewanella frigidimarina can grow anaerobically by utilizing Fe(III) as a respiratory electron acceptor . This results in the synthesis of a number of periplasmic c-type cytochromes, which are absent when the organism is grown in the absence of added Fe(III) . One cytochrome, IfcA, is synthesized when Fe(III) is present as the sole respiratory electron acceptor or when it is present in combination with oxygen, fumarate, or nitrate . The ifcA gene was thus selected for a study of iron-responsive gene regulation of respiratory proteins in S . frigidimarina . The monocistronic ifcA gene clusters with two other monocistronic genes, ifcO, encoding a putative outer membrane porin, and ifcR, encoding a putative transcriptional regulator of the LysR superfamily . Analysis of transcription of all three genes under a range of growth conditions in the wild type and an ifcR insertion mutant and analysis of a strain that constitutively expresses ifcR revealed that iron regulation is exerted at the level of ifcR transcription . In the presence of Fe(III) IfcR is synthesized and acts positively to regulate expression of ifcO and ifcA . Control of Fe(III) respiration by this novel regulatory system differs markedly from Fur-mediated regulation of iron assimilation, in which Fur serves as an Fe(II)-activated repressor . 1-Methylguanosine-Deficient tRNA of Salmonella enterica Serovar Typhimurium Affects Thiamine Metabolism. Glenn R. Björk, 2003.In Salmonella enterica serovar Typhimurium a mutation in the purF gene encoding the first enzyme in the purine pathway blocks, besides the synthesis of purine, the synthesis of thiamine when glucose is used as the carbon source . On carbon sources other than glucose, a purF mutant does not require thiamine, since the alternative pyrimidine biosynthetic (APB) pathway is activated . This pathway feeds into the purine pathway just after the PurF biosynthetic step and upstream of the intermediate 4-aminoimidazolribotide, which is the common intermediate in purine and thiamine synthesis . The activity of this pathway is also influenced by externally added pantothenate . tRNAs from S . enterica specific for leucine, proline, and arginine contain 1-methylguanosine (m1G37) adjacent to and 3' of the anticodon (position 37) . The formation of m1G37 is catalyzed by the enzyme tRNA(m1G37)methyltransferase, which is encoded by the trmD gene . Mutations in this gene, which result in an m1G37 deficiency in the tRNA, in a purF mutant mediate PurF-independent thiamine synthesis . This phenotype is specifically dependent on the m1G37 deficiency, since several other mutations which also affect translation fidelity and induce slow growth did not cause PurF-independent thiamine synthesis . Some antibiotics that are known to reduce the efficiency of translation also induce PurF-independent thiamine synthesis . We suggest that a slow decoding event at a codon(s) read by a tRNA(s) normally containing m1G37 is responsible for the PurF-independent thiamine synthesis and that this event causes a changed flux in the APB pathway .
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