|
|
|
|
|
|
Characterization of a Novel Intracellular Endopeptidase of the  /ß Hydrolase Family from Streptomyces coelicolor A3(2).István Nagy, 2003.In a proteasome-lacking mutant of Streptomyces coelicolor A3(2), an intracellular enzyme with chymotrypsin-like activity, absent from the wild type, was detected . Complementation that restored proteasome function did not suppress expression of the endopeptidase . Since the enzyme was not found in two other S . coelicolor proteasome mutants, its expression probably resulted from a secondary mutation arisen in the proteasome mutant . Purification of the endopeptidase revealed its identity to SCO7095, a putative hydrolase encoded by the S . coelicolor A3(2) genome with no known homologue . Based on the prediction of a Ser-Asp-His catalytic triad and an /ß hydrolase fold, SCO7095 was assigned to peptidase clan SC . N-terminally His-tagged SCO7095 was efficiently expressed in Escherichia coli cells and purified for further characterization . Although SCO7095 is distantly related to several proline iminopeptidases, including Thermoplasma acidophilum tricorn-interacting F1, no aminopeptidase activity was detected . On synthetic substrates, the monomeric enzyme exhibited not only chymotrypsin-like activity but also thrombin-like activity .
Inactivation of gacS Does Not Affect the Competitiveness of Pseudomonas chlororaphis in the Arabidopsis thaliana Rhizosphere. Heike Schmidt-Eisenlohr, 2003.Quorum-sensing-controlled processes are considered to be important for the competitiveness of microorganisms in the rhizosphere . They affect cell-cell communication, biofilm formation, and antibiotic production, and the GacS-GacA two-component system plays a role as a key regulator . In spite of the importance of this system for the regulation of various processes, strains with a Gac- phenotype are readily recovered from natural habitats . To analyze the influence of quorum sensing and the influence of the production of the antibiotic phenazine-1-carboxamide on rhizosphere colonization by Pseudomonas chlororaphis, a gnotobiotic system based on Arabidopsis thaliana seedlings in soil was investigated . Transposon insertion mutants of P . chlororaphis isolate SPR044 carrying insertions in different genes required for the production of N-acyl-homoserine lactones and phenazine-1-carboxamide were generated . Analysis of solitary rhizosphere colonization revealed that after prolonged growth, the population of the wild type was significantly larger than that of the homoserine lactone-negative gacS mutant and that of a phenazine-1-carboxamide-overproducing strain . In cocultivation experiments, however, the population size of the gacS mutant was similar to that of the wild type after extended growth in the rhizosphere . A detailed analysis of growth kinetics was performed to explain this phenomenon . After cells grown to the stationary phase were transferred to fresh medium, the gacS mutant had a reduced lag phase, and production of the stationary-phase-specific sigma factor RpoS was strongly reduced . This may provide a relative competitive advantage in cocultures with other bacteria, because it permits faster reinitiation of growth after a change to nutrient-rich conditions . In addition, delayed entry into the stationary phase may allow more efficient nutrient utilization . Thus, GacS-GacA-regulated processes are not absolutely required for efficient rhizosphere colonization in populations containing the wild type and Gac- mutants .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
