|
|
|
|
|
|
The bzd Gene Cluster, Coding for Anaerobic Benzoate Catabolism, in Azoarcus sp . Strain CIB. María J. López Barragán, 2004.We report here that the bzd genes for anaerobic benzoate degradation in Azoarcus sp . strain CIB are organized as two transcriptional units, i.e., a benzoate-inducible catabolic operon, bzdNOPQMSTUVWXYZA, and a gene, bzdR, encoding a putative transcriptional regulator . The last gene of the catabolic operon, bzdA, has been expressed in Escherichia coli and encodes the benzoate-coenzyme A (CoA) ligase that catalyzes the first step in the benzoate degradation pathway . The BzdA enzyme is able to activate a wider range of aromatic compounds than that reported for other previously characterized benzoate-CoA ligases . The reduction of benzoyl-CoA to a nonaromatic cyclic intermediate is carried out by a benzoyl-CoA reductase (bzdNOPQ gene products) detected in Azoarcus sp . strain CIB extracts . The bzdW, bzdX, and bzdY gene products show significant similarity to the hydratase, dehydrogenase, and ring-cleavage hydrolase that act sequentially on the product of the benzoyl-CoA reductase in the benzoate catabolic pathway of Thauera aromatica . Benzoate-CoA ligase assays and transcriptional analyses based on lacZ-reporter fusions revealed that benzoate degradation in Azoarcus sp . strain CIB is subject to carbon catabolite repression by some organic acids, indicating the existence of a physiological control that connects the expression of the bzd genes to the metabolic status of the cell . Determining Rates of Change and Evaluating Group-Level Resiliency Differences in Hyporheic Microbial Communities in Response to Fluvial Heavy-Metal Deposition. Kevin P. Feris, 2004.Prior field studies by our group have demonstrated a relationship between fluvial deposition of heavy metals and hyporheic-zone microbial community structure . Here, we determined the rates of change in hyporheic microbial communities in response to heavy-metal contamination and assessed group-level differences in resiliency in response to heavy metals . A controlled laboratory study was performed using 20 flowthrough river mesocosms and a repeated-measurement factorial design . A single hyporheic microbial community was exposed to five different levels of an environmentally relevant metal treatment (0, 4, 8, 16, and 30% sterilized contaminated sediments) . Community-level responses were monitored at 1, 2, 4, 8, and 12 weeks via denaturing gradient gel electrophoresis and quantitative PCR using group-specific primer sets for indigenous populations most closely related to the  -, ß-, and
 -proteobacteria . There was a consistent, strong curvilinear relationship between community composition and heavy-metal contamination (R2 = 0.83; P < 0.001), which was evident after only 7 days of metal exposure (i.e., short-term response) . The abundance of each phylogenetic group was negatively affected by the heavy-metal treatments; however, each group recovered from the metal treatments to a different extent and at a unique rate during the course of the experiment . The structure of hyporheic microbial communities responded rapidly and at contamination levels an order of magnitude lower than those shown to elicit a response in aquatic macroinvertebrate assemblages . These studies indicate that hyporheic microbial communities are a sensitive and useful indicator of heavy-metal contamination in streams .
Elucidation of the Vibrio anguillarum Genetic Response to the Potential Fish Probiont Pseudomonas fluorescens AH2, Using RNA-Arbitrarily Primed PCR. Kim Holmstrøm, 2003.The antagonistic interaction between a potential fish probiont, Pseudomonas fluorescens strain AH2, and its target organism, Vibrio anguillarum, was investigated by studying the genetic response of the target organism when it was exposed to the antagonist . We compared the differential display of arbitrarily PCR-amplified gene transcripts in V . anguillarum serotype O1 when it was exposed to AH2 supernatant with the display of transcripts in nonexposed control cultures . Growth of V . anguillarum was immediately arrested when the organism was exposed to 50% (vol/vol) AH2 supernatant . A total of 10 potentially differentially expressed transcripts were identified . Among these we identified a gene homologous to rpoS that was induced in a dose-dependent manner when V . anguillarum was cultured in media supplemented with sterile filtered supernatant from AH2 . rpoS was also induced when growth was arrested with the iron chelator 2,2-dipyridyl . A chromosomal transcript homologous to vibE that participates in vibriobactin synthesis in Vibrio cholerae was also upregulated during AH2 exposure . This transcript could represent a functionally active gene in V . anguillarum involved in biosynthesis of anguibactin or another V . anguillarum siderophore . On the pJM1 plasmid of V . anguillarum serotype O1, a pseudogene designated open reading frame E (ORF E) that contains a frameshift mutation was previously identified . The gene homologous to vibE identified in this study, interestingly, also has significant homology to ORF E on the amino acid level and does not possess the frameshift mutation . Thus, the chromosomally encoded vibE homologue could fulfil the role of the inactive plasmid-encoded ORF E pseudogene . Addition of Fe3+ to the system eliminated the growth arrest, and the genes homologous to rpoS and vibE were not induced . To our knowledge, this is the first study linking rpoS induction to iron starvation . Taken together, the results of this study suggest that a major part of the antagonistic property exhibited by strain AH2 is caused by the ability of siderophores in the supernatant to efficiently chelate iron, which results in instant iron deprivation of the pathogen V . anguillarum and complete growth arrest .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
