|
|
|
|
|
|
Regulation of L-Alanine Dehydrogenase in Rhizobium leguminosarum bv . viciae and Its Role in Pea Nodules. Emma Lodwig, 2004.Alanine dehydrogenase (AldA) is the principal enzyme with which pea bacteroids synthesize alanine de novo . In free-living culture, AldA activity is induced by carboxylic acids (succinate, malate, and pyruvate), although the best inducer is alanine . Measurement of the intracellular concentration of alanine showed that AldA contributes to net alanine synthesis in laboratory cultures . Divergently transcribed from aldA is an AsnC type regulator, aldR. Mutation of aldR prevents induction of AldA activity . Plasmid-borne gusA fusions showed that aldR is required for transcription of both aldA and aldR; hence, AldR is autoregulatory . However, plasmid fusions containing the aldA-aldR intergenic region could apparently titrate out AldR, sometimes resulting in a complete loss of AldA enzyme activity . Therefore, integrated aldR::gusA and aldA::gusA fusions, as well as Northern blotting, were used to confirm the induction of aldA activity . Both aldA and aldR were expressed in the II/III interzone and zone III of pea nodules . Overexpression of aldA in bacteroids did not alter the ability of pea plants to fix nitrogen, as measured by acetylene reduction, but caused a large reduction in the size and dry weight of plants . This suggests that overexpression of aldA impairs the ability of bacteroids to donate fixed nitrogen that the plant can productively assimilate . We propose that the role of AldA may be to balance the alanine level for optimal functioning of bacteroid metabolism rather than to synthesize alanine as the sole product of N2 reduction . Salmonella Type III Secretion-Associated Protein InvE Controls Translocation of Effector Proteins into Host Cells. Tomoko Kubori, 2002.Salmonella enterica encodes a type III secretion system (TTSS) within a pathogenicity island located at centisome 63 (SPI-1), which is essential for its pathogenicity . This system mediates the transfer of a battery of bacterial proteins into the host cell with the capacity to modulate cellular functions . The transfer process is dependent on the function of protein translocases SipB, SipC, and SipD . We report here that Salmonella protein InvE, which is also encoded within SPI-1, is essential for the translocation of bacterial proteins into host cells . An S . enterica serovar Typhimurium mutant carrying a loss-of-function mutation in invE shows reduced secretion of SipB, SipC, and SipD while exhibiting increased secretion of other TTSS effector proteins . We also demonstrate that InvE interacts with a protein complex formed by SipB, SipC, and their cognate chaperone, SicA . We propose that InvE controls protein translocation by regulating the function of the Sip protein translocases . FimZ Is a Molecular Link between Sticking and Swimming in Salmonella enterica Serovar Typhimurium. Steven Clegg, 2002.Salmonella enterica serovar Typhimurium produces two types of filamentous appendages on its surface . Fimbriae mediate adherence to tissues and cells via receptor-specific interactions, and flagella are the organelles of motility . These appendages play a role in colonization and dissemination, respectively, from infected surfaces and may be important components of bacterial survival . Increased expression of FimZ in serovar Typhimurium resulted in bacteria which were hyperfimbriated but were nonmotile in soft agar . This lack of motility was associated with down regulation of the flhDC master flagellar operon . Therefore, FimZ represents a molecular connection between flagella and fimbrial formation in serovar Typhimurium, indicating that the synthesis of flagella and fimbriae are oppositely controlled . Proteomic Analysis of Wild-Type Sinorhizobium meliloti Responses to N-Acyl Homoserine Lactone Quorum-Sensing Signals and the Transition to Stationary Phase. Hancai Chen, 2003.Proteome analysis revealed that two long-chain N-acyl homoserine lactones (AHLs) produced by Sinorhizobium meliloti 1021 induced significant differences in the accumulation of more than 100 polypeptides in early-log-phase cultures of the wild type . Fifty-six of the corresponding proteins have been identified by peptide mass fingerprinting . The proteins affected by addition of these two AHLs had diverse functions in carbon and nitrogen metabolism, energy cycles, metabolite transport, DNA synthesis, and protein turnover . Two hours of exposure to 3-oxo-C16:1-homoserine lactone (3-oxo-C16:1-HL) affected the accumulation of 40 of the 56 identified proteins, whereas comparable exposure to C14-HL affected 13 of the 56 proteins . Levels of four proteins were affected by both AHLs . Exposure to 3-oxo-C16:1-HL for 8 h affected the accumulation of 17 proteins, 12 of which had reduced accumulation . Of the 80 proteins identified as differing in accumulation between early-log- and early-stationary-phase cultures, only 13 were affected by exposure to 3-oxo-C16:1-HL or C14-HL . These results provide a foundation for future studies of the functions regulated by AHL quorum sensing in S . meliloti and help to establish proteomic analysis as a powerful global approach to the identification of quorum-sensing regulatory patterns in wild-type bacteria .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
